ISO/DIS 19204:2026(en)

ISO/TC 190/SC 4

Secretariat: AFNOR

Date: 2025-12-06

Soil quality — Procedure for site-specific ecological risk assessment of soil contamination (soil quality TRIAD approach)

Qualité du sol — Procédure d'évaluation des risques écologiques spécifiques au site de la contamination des sols (approche TRIADE de la qualité du sol)

© ISO 2026

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Contents

Foreword v

Introduction vi

1 Scope 1

2 Normative references 1

3 Terms and definitions 2

4 Process overview 6

5 Uncertainty and weight of evidence 7

6 Soil quality TRIAD performance 8

6.1 First step: Objective of the investigation (formulating the problem and decision regarding the need of a site-specific risk assessment) 8

6.1.1 General approach 8

6.1.2 Decision 9

6.1.3 Stakeholders involved in an ecological risk assessment 9

6.1.4 Independent quality control 10

6.2 Second step: Basic considerations 10

6.2.1 General approach 10

6.2.2 Assessment criteria 11

6.3 Third step: Practical performance of the soil quality TRIAD 12

6.3.1 General 12

6.3.2 Soil quality TRIAD TIERS 12

6.3.3 Soil quality TRIAD lines of evidence 13

6.3.4 Measurement parameters 15

6.4 Fourth step: Assessments at the different TIERS: scaling, weighting and integrating results 18

6.4.1 General 18

6.4.2 Quantification of results from terrestrial tests 19

6.4.3 Scaling in practise 19

6.4.4 Weighting 19

6.4.5 Integration of results 20

6.5 Fifth step: Decision on how to proceed 20

7 Reporting 21

Annex A (informative) Bioindicators of effect and accumulation — Additional tools for site-specific ecological risk assessment 23

Annex B (informative) Toolboxes 24

Annex C (informative) Case studies 32

C.1 Case Study 1: Former Mining Site Context 32

C.1.1 Context 32

C.1.2 First step: Objective of the investigation (formulating the problem and decision regarding the need of a site-specific risk assessment) 33

C.1.3 Second step: Basic considerations 33

C.1.4 Third step: practical performance of the soil quality TRIAD (TIER 1) 34

C.1.4.1 Presentation of the site and sampling strategy 34

C.1.4.2 Chemical LoE 36

C.1.4.3 Ecotoxicological LoE 36

C.1.4.4 Ecological LoE 36

C.1.4.5 Fourth step: Assessments at the different tiers: scaling, weighting and integrating results (TIER 1) 36

C.1.4.6 Scaling 36

C.1.4.6.1 Chemical LoE 36

C.1.4.6.2 Ecotoxicological LoE 39

C.1.4.6.3 Ecological LoE 40

C.1.4.6.4 Weighting 41

C.1.4.6.5 Integration of results 41

C.1.5 Fifth step: Decision on how to proceed (TIER 1) 41

C.1.5.1 Third step: practical performance of the soil quality TRIAD (TIER 2) 42

C.1.5.2 Chemical LoE 42

C.1.5.3 Ecotoxicological LoE 43

C.1.5.4 Ecological LoE 44

C.1.6 Fourth step: Assessments at the different tiers: scaling, weighting and integrating results (TIER 2) 44

C.1.6.1 Scaling 44

C.1.6.1.1 Chemical LoE 44

C.1.6.1.2 Ecotoxicological LoE 46

C.1.6.1.3 Ecological LoE 46

C.1.6.2 Weighting 47

C.1.6.3 Integrating results 47

C.1.7 Fifth step: Decision on how to proceed (TIER 2) 47

C.2 Case study of Korea 47

C.2.1 Site characterization 47

C.2.2 Soil sampling and sample preparation 48

C.2.3 TRIAD assessment 48

C.2.3.1 Soil characterization 48

C.2.3.2 Chemistry-LoE 48

C.2.3.3 Ecotoxicology-LoE 49

C.2.3.4 Ecology-LoE 49

C.2.3.5 Integrated Risk (IR) 50

Bibliography 51

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

ISO draws attention to the possibility that the implementation of this document may involve the use of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this document, ISO [had/had not] received notice of (a) patent(s) which may be required to implement this document. However, implementers are cautioned that this may not represent the latest information, which may be obtained from the patent database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.

Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISO's adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 4, Biological characterization.

This second edition cancels and replaces the first edition (ISO 19204:2022), which has been technically revised.

The main changes are as follows:

— Revision/update of toolboxes for the different levels of the TRIAD;

— Quantification (scaling) and aggregation of results at different levels;

— Weighting criteria;

— Selection of the reference zone and use of data from this reference zone;

— Practical examples of the use of TRIAD in an informative annex (in progress).

The feedback from stakeholders and engineering consultants which indicates that, while the different steps of the method are sufficiently defined, there is still a need for describing it in a more practical way to facilitate its implementation and reproducibility.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

This document is set up to ensure the quality of the site-specific ecological risk assessment of soil contamination. This process was described previously in a report by the Dutch PGBO (Integrated Soil Research Programme Agency), continued in the current SKB (Foundation for Soil Knowledge Development and Transfer).^[69] The present document is based on these Dutch reports but has been shortened in order to increase its general applicability. In addition, parts of the ecological risk assessment framework for contaminants in soil prepared by the British Environment Agency^{[21][22][23][24][25][26][27]} were considered (this tiered framework does use the same three Lines of Evidence (LoE) as the TRIAD but not in parallel but consecutively). Experiences from various other sources,^[29][30][68] in particular, a summary of a Danish study performed as part of the EU FP6 project Liberation,^[36] as well as a Danish report,^[35] were added.

The term TRIAD relates to the following three LoE’s: chemistry, ecotoxicology and ecology.^[10] Originally, it was described as Sediment Quality TRIAD by Long and Chapman.^[38] The TRIAD does not particularly consist of three lines of evidence (up to five have been proposed^[11]) but in specific situations, two might be sufficient. Descriptions of the soil quality TRIAD approach in the context of soil contamination are given, for example, in References^[36],^[40],^[55],^[59],^[60],^[63],^[69],^[71] and.^[73] It should be mentioned that the soil quality TRIAD is not only used in Central Europe but also in other regions, for example, in Portugal,^[1] Italy,^[67] Brazil^[44] or South Korea.^[117][118] These publications can be used as case studies for the application of the soil quality TRIAD.

NOTE Recently, the ecological risk assessment procedures in The Netherlands, Norway, Sweden and the United Kingdom were compared.^[35] The basic ideas of the TRIAD approach [e.g. a tiered approach and the combination of information from different disciplines (chemistry, ecotoxicology, and ecology)] have been accepted in these countries. However, only in the United Kingdom^{[21][22][23][24][25][26][27]} and The Netherlands^{[40][43][53][58][60][61][63]} have detailed frameworks been developed. The overall structure of this document combines and modifies both national frameworks in order to provide guidance independently from the country or region where the site to be assessed is located. The terminology of this document does follow the approach described in the EU project Liberation^[36].

Soil quality — Procedure for site-specific ecological risk assessment of soil contamination (soil quality TRIAD approach)

This document describes in a general way the application of the soil quality TRIAD approach for the site-specific ecological risk assessment of contaminated soils. In detail, it presents in a transparent way three lines of evidence (chemistry, ecotoxicology and ecology) which together allow an efficient, ecologically robust but also practical risk assessment of contaminated soils. This procedure can also be applicable to other stress factors, such as acidification, soil compaction, salinization, loss of soil organic substance, and erosion. However, so far, no experience has been gained with these other applications. Therefore, this document focuses on soils contaminated by chemicals.

NOTE 1 This document focuses on ecological risk assessment. Thus, it does not cover human health end points.

In view of the nature of this document, the investigation procedure is described on a general level. It does not contain details of technical procedures for the actual assessment. However, this document includes references relating to technical standards (e.g. ISO 15799, ISO 17616) which are useful for the actual performance of the three lines of evidence.

In ecological risk assessment, the effects of soil contamination on the ecosystem are related to the intended land use and the requirements that this use sets for properly functioning soil. This document describes the basic steps relating to a coherent tool for a site-specific risk assessment with opportunities to work out site-specific details.

This document can also be used for the evaluation of clean-up operations, remediation processes or management measures (i.e. for the evaluation of the environmental quality after having performed such actions).

NOTE 2 The application of this document starts when it has already been decided that an ecological risk assessment at a given site needs to be performed. In other words, the practical performance of the soil quality TRIAD and the evaluation of the individual test results will be described. Thus, nothing will be said about decisions whether (and if yes, how) the results of the assessment are included in soil management measures or not.

NOTE 3 The TRIAD approach can be used for different parts of the environment, but this document focuses mostly on the soil compartment. Comparable documents for other environmental compartments are intended to be prepared in addition (e.g. the terrestrial aboveground compartment) in order to perform a complete site assessment, based on the same principles and processes.

There are no normative references in this document.

For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/

3.1

stakeholder

person or party with an interest in the soil quality (3.21) of a potentially contaminated site

Note 1 to entry: The composition of the stakeholder group depends on the specific local conditions.

3.2

assessment criteria

criteria set up to decide if a site requires further investigation or other action (e.g. remediation)

Note 1 to entry: They can be drawn up by the competent authority (3.3), the stakeholders (3.1) and the investigators for the interpretation of the results of the soil quality TRIAD study before the investigation is carried out. Two criteria could be distinguished, namely:

a) threshold that marks the boundary between adequate and inadequate removal of uncertainties in the assessment;

b) threshold that marks the boundary between an effect that is considered acceptable and one that is not considered acceptable, based on a reference or a limit value.

Note 2 to entry: Assessment criteria are necessary for every collection of ecological conditions (for example, all species in a generic system, a key species or a protected species).

3.3

competent authority

part of the authorities that is responsible for the implementation of the soil clean-up operation

Note 1 to entry: Depending on the site and the country, the competent authority could be very different. The competent authority assesses investigation results and takes decisions via decrees about the severity and urgency of the soil contamination found. The competent authority also assesses the clean-up plans of the clean-up teams on their own initiative (for example, companies).

3.4

soil management

all the anthropogenic activities that influence the soil system at the site to be assessed

Note 1 to entry: This can include choices in land use (3.5) (e.g. groundwater level management, nature management, park management, loading with soil-contaminated substances).

3.5

land use

using the ecosystem services (3.8) that the soil provides

3.6

land user

person or group of people who uses the ecosystem services (3.8) of the soil, whereby in the role allocation, the larger spatial scales are generally represented by organizations, societal parties and authorities

3.7

ecological effect

change to an aspect of the ecosystem caused by anthropogenic stress factors (3.15)

Note 1 to entry: Changes [see also assessment criteria (3.2)] to an ecosystem as a result of the presence of contaminants are regarded as negative changes regardless of the direction. In this document, the three lines of evidence (LoE) in accordance with the soil quality TRIAD approach are required for the effect to be determined. In addition, the variation in space, time and parameters is also important. See also type 1 error (3.17).

3.8

ecosystem service

service that is (directly or indirectly) provided by an ecosystem.

Note 1 to entry: The Ecosystem Service Approach is becoming more and more the theoretical basis for the definition of protection goals in the context of the risks of chemicals in the environment (e.g. EFSA 2012), including the risk assessment of contaminated soils (e.g.[2],[41], and[74]).

Note 2 to entry: Examples of ecosystem services that the soil provides to people are agricultural products, clean surface water, groundwater and drinking water, and a healthy environment in which to live. The provision of many of these services depends in many cases on the activity of diverse organism communities, e.g. degradation of contaminants in soil by microbes, meaning that groundwater is kept clean^[75].

Note 3 to entry: Some soil functions (organic substance composition and degradation, natural self-cleaning ability of the soil and soil structure for a good rooting of vegetation and crops) are counted as ecosystem services in this context. In detail, four basic soil services are distinguished, namely, soil fertility, resistance to stress and adaptation, the soil as a buffer and reactor, and biodiversity. The Millennium Ecosystem Assessment^[41] distinguishes at ecosystem level regulating services (regulation of ecosystem processes), provisioning services (products), cultural services (non-material benefits) and support services (for the provision of all the other ecosystem services).

3.9

generic assessment

assessment of a site using a general investigation method that is not geared to the properties of the site

3.10

site-specific assessment

assessment of a site using an investigation method that is partially geared to the properties of the site

Note 1 to entry: The assessment consists of a combination of generally applicable and possibly specifically developed (tailor-made) parts. The interpretation of the results of the investigation is site-specific and can be generalized only to a limited extent [see also generic assessment (3.9)].

3.11

site-specific model

description of the local ecosystem and of the intended land use (3.5) in terms of ecological conditions for this use, and of the nature and spread of the contamination.

Note 1 to entry: This model makes it clear which exposure routes are relevant for aspects of the ecosystem that are needed for the land use (3.5). Suitable parameters can then be selected for the soil quality TRIAD study with optimum weight of evidence (3.20) and support^[70].

3.12

uncertainty

degree of doubt about the assumptions or investigation results, to be broken down in the case of the assessment of the ecological risks of soil contamination into: communications uncertainty, model uncertainty (epistemic uncertainty), uncertainty because of variation and uncertainty in decision-making

Note 1 to entry: For the different types of uncertainty, see also Clause 5.

3.13

reference

part of a site, of a sample or of a group of literature data that acts as a benchmark for the effect scale (the baseline, measure or standard)

Note 1 to entry: It is a description of the condition of the soil in quantitative and qualitative terms that can be used as part of the measure for the soil quality (3.21) to be assessed. The ideal reference is identical to the site (or the sample) to be assessed, the only difference being that the stress factor (3.15) to be assessed is missing. Chemical, physical and biological aspects form partial aspects of the reference. For a site-specific application, site-specific details are needed to obtain an accurate reference. A reference is preferably chosen at the investigation site; measurements are then preferably taken at the same time as the samples/measurements to be assessed. If no comparable clean reference is available, the least contaminated sample can also be chosen (for example, in a gradient), on condition that the sample is regarded as being sufficiently representative to be used as a reference. A reference can also be based on samples of a comparable site elsewhere or on literature data (= virtual reference).

3.14

scaling

process in which measurement or model data are interpreted using a measure intended for this purpose

Note 1 to entry: When applying the soil quality TRIAD (3.16), assessment data are generated to ascertain an effect on the level of the ecosystem as quantitatively as possible. A practical, standardized scale runs from 0 to 1 or from 0 % to 100 %. 0 or 0 % represents no effect and 1 or 100 % represent the maximum theoretical effect at a high concentration of the contaminating substances. Sometimes, only a low level of quantitative scaling is possible, such as on an ordinary scale or on a 2 or 3 point scale (yes/no or yes/maybe/no). These low quantitative scaling methods can be used in a weight‑of‑evidence (WOE) (3.20) approach. Examples of scaling are given in, e.g. Reference [40].

3.15

stress factor

outcome of an anthropogenic activity that has a possible negative effect on the ecosystem, such as chemical soil contamination, overfertilization, desiccation or soil compaction.

3.16

soil quality TRIAD

procedure for a site-specific ecological risk assessment, whereby the weight of evidence (WOE) (3.20) is made up of three independent lines of evidence (LoE):

1) a line of evidence based on environmental chemistry with data about concentrations of toxic substances being converted into the expected effect on the ecosystem;

2) a line of evidence based on measurements of the ecotoxicity in samples of the site with tests; and

3) a line of evidence based on observations of the ecosystem at the site that focus on demonstrating the effects caused by the contamination

Note 1 to entry: The total of these elements is more than the sum of the separate parts because the burden of proof is partly based on consistency between the elements.

Note 2 to entry: Descriptions of the approach of the soil quality TRIAD study applied to soil contamination are given in References [36], [40], [59], [60] and [63], among other places. For the choice of tests, see also ISO 17616.

3.17

type 1 error

judgment that unjustly concludes that there is an unacceptable effect

Note 1 to entry: The term comes from statistics. If there is a type 1 error, the assessment is based not on an actual unacceptable effect but on chance or a model error. The risk of a type 1 error occurring can be reduced by making more observations or by improving the model with the ecological aspects and indicators. This latter option can be achieved by choosing improved conditions and investigation parameters.

3.18

type 2 error

judgment that unjustly concludes that there is no unacceptable effect

Note 1 to entry: The term comes from statistics. If there is a type 2 error, there is actually an unacceptable effect, but this effect has not been demonstrated because of insufficient or incorrect investigation efforts (too few observations, unsuitable reference(s) or model errors).

3.19

weighting

rating various investigation results transparently, with equal or different weight being given to the information concerned

Note 1 to entry: A simple starting position is to give equal weight to the results of the various assessment parameters. This can be deviated from to devote attention to specific ecological conditions [protected species, key species, processes, ecosystem services (3.8)], to relatively reliable parameters, or to special test results (giving weight to observations that show a great effect or giving extra weight to measurements of bioavailable concentrations).

3.20

weight of evidence

WOE

weight of evidence of the soil quality TRIAD study which can be used as the basis for taking decisions responsibly.

Note 1 to entry: In this document, WOE is meant above all in the methodological sense, with all available data obtained from various lines of evidence-taking being involved in the final conclusion, possibly on the basis of quantitative weighting. Background information about scaling (3.14), weighting (3.19) and WOE can be found in References [12], [16], [40], [53], [67], and [72].

Note 2 to entry: With a set budget for the soil quality TRIAD study, the WOE needs to be optimized across investigation parameters and sample intensity. The assessment criteria (3.2) per parameter and the acceptable statistical error margin [type 1 error (3.17)] is chosen such that the WOE and acceptance of possible results of the investigation by the stakeholders (3.1) are maximized.

3.21

soil quality

capability of a type of soil, within natural or managed ecosystem boundaries, to function and provide ecosystem services

[SOURCE: ISO 18718]

3.22

screening value

soil value which, if exceeded, indicates an assumed potential effect on soil biological structure and function

3.23

retention function

ability of soils/soil materials to adsorb pollutants in such a way that they cannot be mobilized via the water pathway and translocated into the food chain

Note 1 to entry: The habitat and retention functions include the following soil functions according to ISO 11074:

— control of substance and energy cycles as components of ecosystems;

— basis for the life of plants, animals and man;

— carrier of genetic reservoir;

— basis for the production of agricultural products;

— buffer inhibiting movement of water, contaminants or other agents into the groundwater.

3.24

socio-ecosystemic issues

the issues surrounding socio-ecological systems are seen here as the need to preserve the functioning and services of these complex systems involving biophysical components (ecology, hydrology, etc.) and societal components (economy, public policies, institutions, etc.) in constant interaction.

3.25

intrinsic uncertainties

uncertainties of the study related to the choices made in the design of the study protocols (analyses, equipment, sampling, etc.).

3.26

stochastic uncertainties

uncertainties which essentially reflect the intrinsic variability of the quantity in question (e.g. variations in earthworm abundance over time). These uncertainties can be better described by obtaining additional data.

3.27

epistemic uncertainties

uncertainties which essentially reflect a lack of knowledge. It is possible to reduce these uncertainties by obtaining additional data.

[SOURCE:ISO 2394:2015, 2.2.19, modified]

3.28

habitat function

ability of soils/soil materials to serve as a habitat for microorganisms, plants, soil living animals and their interactions (biocenoses)

The main five steps of performing a soil quality TRIAD according to this document are summarized in Figure 1. Only the performance of the soil quality TRIAD itself (= execution phase in Reference [43]) is described.

The method is based on the decision whether and how soil quality shall be assessed at a specific site, including socio-ecosystemic issues (3.24). (Step I) (also called the phase of the development of a Conceptual Site Model (CSM).^[21][22] In case this decision is positive, the three lines of evidence, here abbreviated as chemistry, ecotoxicology and ecology, will be performed (Steps II to IV). Based on an integrative assessment of the results of the investigation, a decision, e.g. regarding soil remediation, can be made (Step V). This document refers primarily to Steps I to IV (Step V is not covered in detail in this document). Note that the extent of the input from stakeholders (left side in Figure 1) and risk assessors (right side in Figure 1) differ in the different steps — but in any step, input from both sides is required.

NOTE 1 The description of the performance of the soil quality TRIAD as described in this overview can be considered as the “ideal” version (e.g. the steps and tiers are performed one after another). However, in reality, depending on the contamination and site properties, the different steps might be performed in a more flexible way. In addition, as soon as a decision on the ecological risk of a specific site is possible, the process can be stopped.

NOTE 2 Annex A describes the use of bioaccumulation data as an additional tool for site-specific ecological risk assessment.

Key

C chemistry

T ecotoxicology

E ecology

NOTE For details of the central (technical) part of the TRIAD approach, see also Figure 2.

Figure 1 — Diagram of the five steps to be carried out for site-specific ecological risk assessment
(soil quality TRIAD) of soil contamination supporting decision-making with regard to soil quality

Uncertainty is a key factor in the assessment of ecological risks. Detailed description of uncertainties in a TRIAD report is mandatory in order to manage them more effectively and also to strengthen the conclusions of the risk assessment by addressing its obvious limitations. An assessment of ecological risks has various uncertainties^[65].

— Communication uncertainty. This form of uncertainty may occur if experts communicate with land users about ecological risks.

EXAMPLE Translation of a question from a stakeholder (e.g. Is there an ecological risk and how great is it?) into a scientific question, and communication about the results of the assessment. This uncertainty can be reduced by good coordination between stakeholders and experts.

— Model uncertainty. Models are used in risk assessment to simplify the local ecosystem (also called site-specific models). The assessment is based on indicators that are used to describe this simplified system in quantitative or qualitative terms. The model uncertainty is then linked to the obvious incompleteness of the model, partly as a result of conscious choice, partly as a result of ignorance. (intrinsic uncertainties)

EXAMPLE A certain plant can be chosen as a model for all the plants in the ecosystem. The chosen plant is not always an averagely sensitive plant or a sufficiently exposed type of plant and is therefore sometimes not representative. The model organism does not exclude effects on other species.

— Uncertainty as a result of variability. Uncertainty that results from variations at the sites in time and space, and from variations and errors in the measurements. (stochastic and epistemic uncertainties)

EXAMPLE An investigation is a snapshot in time, whereas ecosystems change over seasons and years.

The soil quality TRIAD advocated in this document, as the content-based and technical framework for the risk assessment, is based on an optimized weight-of-evidence (WOE) approach. It is made transparent and quantifiable in the integration of the three independent lines of evidence. If the three independent lines of evidence point in roughly the same direction (e.g. quantified on a scale from 0 to 1), this is a strong indication that the model uncertainty is slight and the investigation can be completed. If the three independent lines of evidence do not point in the same direction, the model uncertainty is still great and a new stage needs to be gone through to reduce the model uncertainties sufficiently. The model uncertainty can, for example, be quantified using a deviation factor^[40].

The soil quality TRIAD is not intended to reduce communication uncertainties, although it can be used for this. In theory, the results of the soil quality TRIAD are easy to communicate and to summarize in ecological terms as the biological characteristics of the ecosystem are also involved in the assessment at the site itself. In practice, the results of the individual lines of evidence shall be communicated too in order to achieve full understanding of the final results.

The decision whether a TRIAD has to be performed or not for a certain potentially contaminated site is part of an ecological risk assessment (ERA). Details of such an ERA differ on the national level, but this decision is based on information compiled in a document often entitled as Conceptual Site Model (CSM). This term has been introduced in the United Kingdom for the first step of an ecological risk assessment framework for contaminants in soil.^{[21][22][23][24][25][26][27]} All available relevant information about the site to be assessed, e.g. the intended (current and/or future) soil management, the soil ambitions of local government (including the future use of the land), and the possible ecosystem stress that may be caused by the soil contamination, is used in this desk study. This step also contains the identification of sources of contamination, ecological receptors of concern and the potential pathways of exposure. If available, the results of the more detailed soil investigation provide the scope and the spatial distribution of the soil contamination. If a soil quality map (e.g. a map of the occurrence of contaminants) is available, this can be an important source of additional information with regard to the soil quality in the area.

This whole set of information can be divided into three sources:

a) know-how and information provided by the societal, policy and administrative parties (including the owner of the site);

b) input from experts (e.g. having experience in the specific region, contamination or ecology);

c) data from scientific (field or laboratory) investigations or from the literature.

The decision about the subject and objective of the investigation should be made as clear as possible and the investigation objective should be “SMART”:

— Specific: accurately described so that all the people concerned recognize the same objective;

— Measurable: quantifiable units are used for the assessment of the ecological risks;

— Achievable: the objective is recognized by all the parties involved;

— Realistic: financial conditions and other, e.g. legal, restrictions are taken into account;

— Time-related: at the start, it is clear when the investigation objective should be achieved and how any exceeding of the deadline should be dealt with.

In any case, the investigation effort has to be related to the size of the contaminated site as well as the severity and complexity of the potential ecological risk. The starting point is that the investigation effort is in real proportion to the size of the problem and the uncertainty that (still) exists.

Note that such a decision depends strongly on national regulations and practices which can be very different in individual countries.

Parties with an interest in the soil quality at the site (stakeholders) are the following:

— users (local, regional, national and societal);

— responsible bodies (competent authority, government);

— owners (finance).

Other parties (without a direct interest in the soil quality at that specific site) are the following:

— experts (soil experts, ecologists, ecotoxicologists, risk assessors);

— investigators (responsible for the implementation of the investigation);

— consultants (writers, process consultants, mediators, communication employees).

Several of these parties or roles may also be combined in one person.

At a small investigation site (e.g. a small landfill site), the input of the stakeholders and the experts can remain limited. At a major investigation site (e.g. the area of a former chemical production plant or a shooting range), the role of the stakeholders should be broken down into the different interested parties.

NOTE The difference between “small” and “major” investigation sites depends strongly on the specific situation in a region or country.

At all times, a clear, traceable and transparently reported distinction should be drawn between the role of the stakeholders and the input of know-how by investigators and consultants, preferably (and dependent on size) also with tasks being divided among different people. Details of these roles should be fixed in the investigation plan.

The way stakeholders can be involved and have to be involved depends on the national regulations and practice.

Since the decisions based on the performance of the soil quality TRIAD can have far-reaching consequences both in legal as well as in financial terms for stakeholders involved, the quality of the work and the gained data have to be ensured. Obviously, all reference and validity criteria required by the various technical standards (e.g. analytical methods, ecotoxicological tests, etc.; usually available as ISO publication) shall be fulfilled. In addition, the investigation plan, the implementation of the investigation, the integration of the data from the three lines of evidence, their evaluation and the reporting should be documented according, e.g. to the requirements of ISO/IEC 17025, i.e. ideally the organizations performing a soil quality TRIAD should be accredited. However, details of the implementation of quality assurance cannot be described here because of differences in individual countries.

In Step II, the initial part of the practical investigation mainly consists of the evaluation of detailed information which is necessary for the individual tests, analyses and investigations within the soil quality TRIAD. These practical steps will then be laid out in a formal investigation plan. It is important that it is clear in advance what the opportunities and restrictions of the investigation are and that there is a consensus in advance about the design of the practical work as well as the interpretation of the results. The information required for the investigation plan focuses mainly on two points [see 1) and 2) below], assuming that all relevant information describing the study site (e.g. maps, climate data, history on usage and contamination) has already been compiled in Step I when making the decision that an ecological risk assessment is necessary:

1) Ecological conditions:

The ecological conditions, which could be at risk because of the contamination, shall be identified. These ecological conditions (including the land use) determine which ecosystem services are provided by the soil at a specific site,^[7][15] its biodiversity, in particular the occurrence of key or protected species,^[75] and any objectives specifically mentioned by land users. In addition, it has to be checked whether surrounding areas are specifically protected by law.

2) Critical aspects of ecological conditions:

It shall be decided which aspects of the ecosystem the investigation is to focus on, based on the ecological conditions identified already. These critical aspects depend on the specific vulnerability caused by soil contamination. Existing literature and expertise form the information source for this. Both structures (= biodiversity) and processes (= functions of the soil organism community), including the ecosystem services provided by the organism community, will preferably be used when selecting the individual measurement parameters.

NOTE In the UK framework, this step is described in detail, i.e. the identification of ecological receptors of potential concern [e.g. species of special (protection) interest] or direct/indirect pathways of potential concern^[22].

Agreements between the competent authority, the stakeholders and the investigators shall be made about the way in which the results of the soil quality TRIAD study will be assessed for all three LoEs (these agreements have to be recorded in the investigation plan). This is about limiting and dealing with uncertainties in the results of the investigation. A focused investigation (e.g. a tiered approach when performing practical studies) will reduce this model uncertainty. An adequate reduction of uncertainty is required for scientific underpinning of the decision-making about soil management or clean-up. The agreements should relate at least to the following:

a) The establishment of a measure using reference data. To this end:

— a suitable reference should be selected for each investigation parameter either measured or derived (preferably site-specific or area-specific); this reference will act as the 0 % level on the effect scale;

— a (possibly theoretical) 100 % effect level will be defined for each investigation parameter;

— for each investigation parameter, it shall be decided how the measurement will be scaled from 0 % to 100 % (for example, a linear relation) or how a stimulation will be interpreted (0 % effect or an effect resulting from a plausible relationship with contamination effects that are assessed negatively). With a WOE approach (see 3.20), the extremes of the measure (the first two of the above dashes) are more important for the assessment than the relationship between the two extremes.

For an assessment with the soil quality TRIAD, an adequate scaling is essential for the integration of data from three different independent lines of evidence.

b) Design with weighting factors for the various investigation parameters.

A starting point could be an equal weighting of the assessment parameters to be distinguished within the soil quality TRIAD lines of evidence and an equal weighting of the three soil quality TRIAD lines of evidence.

c) Agreements about reducing uncertainties in the risk assessment.

They are reduced by a) taking variations into account and b) taking model uncertainties into account. Both uncertainties can be reduced in various ways. For each investigation parameter, the optimum sampling strategy and sample size can be determined in relation to the expected (natural) variation. Model uncertainties could be reduced by selecting more and better parameters. The aim is to limit both type 1 and type 2 errors as much as possible.

d) The derivation of assessment criteria for uncertainty, a reduction of model uncertainties as a result of the WOE approach (soil quality TRIAD) and unacceptable effects. In principle, the assessment should focus on the reduction of uncertainties. Once the uncertainties have been sufficiently reduced, the system can be assessed using the integrated investigation results. As a WOE in the soil quality TRIAD study consists of three lines of evidence, integration is always needed.

When the above work has been completed, the definitive investigation plan is drawn up, which includes the agreements concluded about the investigation design, the assessment criteria and the interpretation of the investigation results. After agreement by the stakeholders, the investigation plan is submitted to the competent authority. Consultation with this authority is recommended but approval of the planned study is not mandatory.

NOTE Involving the competent authority as early as the initial discussions on the investigation plan can avoid the investigation plan having to be explained again and modified. The role of the competent authorities can differ considerably in different countries.

The soil quality TRIAD is a powerful weight-of-evidence approach originally developed to evaluate sediment quality.^[38] In the terrestrial compartment, less experience is available on the practical use of the soil quality TRIAD.^[36] The investigation is performed according to the investigation plan as laid down in 6.2. Reporting of the investigation results should meet the requirements set out in Clause 7. In the following, the overall structure of the soil quality TRIAD (i.e. as a tiered process), the three lines of evidence as part of a WOE approach and appropriate methods for each tier and each line of investigation (so-called tool boxes) are described

The soil quality TRIAD can include different TIERS in which each consecutive tier is increasingly fine-tuned to the site-specific situation. In the first TIER, the research is simple, broad and generic. In later TIERS, more specific and complex tests and analyses may be used. The tiered approach is chosen for several reasons, the most important of which is cost-effectiveness. Each subsequent tier is characterized by an increasing complexity (see Figure 2), i.e. both ecological reality but also efforts and resources needed increase when going from TIER 1 to TIER 3. If amount and quality of data are high (i.e. uncertainty is low) when assessing the results of any given TIER of the soil quality TRIAD, then the ecological risk assessment may be finished and actions taken if needed (see Figure 2). If there is still a high level of uncertainty (indicated e.g. by conflicting results from the three lines of evidence) or the result of the assessment is not acceptable, more investigations are desirable in a higher TIER. The information from previous tiers can be used in the assessment of the next one. At the end of each tier, an assessment is made. In this assessment, all available results will be used including the results from previous TIERS. Data should not be considered when further research has shown that a result is not reliable, e.g. when the validity criteria are not met due to low quality of the test organisms or high temperature fluctuations in a climate chamber.

In any case, work in this tiered approach ends when there are sufficient data for a final assessment to be performed in Step IV.

At each soil quality TRIAD step, different methods from the three lines of evidence can be used. If considered most cost-effective, it is always possible to stop further investigations after each TIER and either re‑define the land use or if needed take necessary actions to remediate or prevent dispersion of contaminants.

Figure 2 — Schematic view of the tiered approach when performing a soil quality TRIAD study

The soil quality TRIAD approach consists of three lines of evidence (LoEs) (often called “legs” in the literature), i.e. chemistry, ecotoxicology and ecology (see Figure 3). These LoEs can be defined as follows.

Figure 3 — Schematic view of the three lines of evidence (LoEs) of the soil quality TRIAD
(in brackets: rough indication of the main methodological approach)

Chemistry (also called environmental chemistry or residue analysis)

In this LoE, the presence of contaminants in the environment is measured, most importantly in the soil itself. Both total concentration and environmentally bioavailable fractions can be measured, which could be presented, for example, as mg/kg soil dry mass or as µg/l pore water (the latter is relevant for the assessment of the retention function, i.e. when testing aquatic organisms). In the original TRIAD approach, only total concentrations were measured. Now, methods are available to measure the (bio)available or accessible fractions (e.g. ISO 17402). In combination with soil characteristics (e.g. ISO 18772) and modelling approaches, an improved estimate of the riskful fraction can be made. In addition, concentrations accumulated in biota, or modelled via food-chains, are used for the calculation of risks on the basis of toxicity data from the literature (see Bibliography). The measured concentrations can be compared in a first assessment with soil screening values (SSVs). These SSVs have been derived from results of ecotoxicological tests (mainly performed in the laboratory), independently from each other in various countries (e.g. The Netherlands,^[69] Denmark,^[66] Germany,^[3] or the United States^[76]). Their legal status varies from country to country, but often they play an important role as the first measure to assess the quality of a soil. Besides these values, valid for whole countries or regions, site-specific SSV (e.g. for specific soils) could be prepared but in this case, enough test data with these soils have to be generated. SSVs are usually based on (often the same or similar) test data and are derived using the SSD approach (species sensitivity distribution),^[9][54] meaning that the values themselves do not differ considerably. However, their use in legislation can clearly differ. In higher tiers, concentrations based on specific extraction procedures (both in soil or biota) could be used. When adopting any chemical method based on the concept of bioavailability, it is necessary that a corresponding reference system based on ecotoxicity test data has been developed (differentiated for each chemical contaminant)^[4].

Ecotoxicology (often called toxicology)

Tests (sometimes called bioassays) with many different groups (mainly microbes) or species (mainly nematodes, oligochaetes, insects, mites or snails but also plants, see Annex B for suitable tests) are carried out in order to measure the actual toxicity present in environmental samples from the test site. To do so, standard guidelines [mainly ISO, e.g. ISO 15799, ISO 17616, but in North America also EPA (US Environmental Protection Agency) and EC (Environment Canada) guidelines] are commonly used. Recent compilations of suitable test methods have been published by Environment Agency^[27] and Environment Canada,^[28] which also include guidance for sampling and preparation of soils. Even broader is ISO 17616,^[24] which provides an overview not only on ISO test guidelines but also strategic issues (e.g. which tests are most useful in which situations) as well as interpreting the results of these tests. The number of tests is still growing but it seems that the increase is slowing down, since most microbial functions as well as many representatives of soil invertebrate groups or plants have already been identified as test organisms. Tests with acute end points (especially mortality) are usually suitable for TIER 1. Chronic tests with their higher ecological relevance are more appropriate for higher TIERs and are more often required in newer legislations. However, there are still some gaps in the battery of soil test organisms (e.g. isopods; see e.g. Reference [77]), especially when looking at non-temperate regions of the world. Since most of the test species were selected for the study of the effects of individual chemicals in highly standardized laboratory tests, often using OECD Artificial Soil, there is a lack of knowledge on their behaviour in natural field soils. However, this situation is currently improving (e.g. References [20], [34], [42], and [57]), meaning that today such tests are possible to be performed in the majority of temperate (probably including Mediterranean) soils. In the ecotoxicological risk assessment of contaminated soils, these tests are used directly (i.e. by using soil from the test site) but also indirectly, since results from the same tests have been used to derive the SSVs mentioned above when describing the work performed in the chemistry LoE. Last but not least, it has to be mentioned that biomarkers have often been proposed as possible end-points in this context (mainly for screening purposes); so far no individual methods have been internationally validated or standardized [for a critical evaluation of test methods (including biomarkers), see References [20] and [40]].

Ecology

In this LoE, many different methods can be used, which most often are directly taken over from ecology. Best known are the methods to assess the aboveground vegetation at a test site, often collectively known as plant sociology (first compiled by Braun-Blanquet^[6]; e.g. for Central Europe, see also Reference [18]). It is still one of the few methods which can be used by simply walking over the test site, while determining the species composition and growth of plants. In the case of soil organism methods, they are usually known for many years but only very few have been standardized so far. Most notably, a recent compilation from Canada^[28] as well as ISO 23611‑1 to ISO 23611‑6, focusing on the sampling of various soil invertebrates [earthworms, micro-arthropods, enchytraeids, nematodes, soil macrofauna (e.g. diplopods, isopods)] and the design of such studies, have been published. However, ISO 23611‑6 is more of a guidance paper, since the design of almost any site-specific monitoring differs, depending on the specific objectives of the investigation and the characteristics of the test site, in particular the ecological conditions in combination with the extent and history of the contamination. Therefore, any standardization will certainly be limited in this area.

Field ecological observations are performed at the contaminated site and the results are compared to some kind of reference (or benchmark). The ideal reference is identical to the test site (or the test soil sample) to be assessed, the only difference being that the stress factor to be assessed is missing. However, this is not always possible. Alternatively, a virtual reference can be defined, which is based on the investigation of several uncontaminated sites which in terms of land use, climate, and soil properties are similar to the test site (for an overview on this approach, see Reference [56]). Recent compilations of biological soil monitoring in Europe have been published (see References [31], [61], [62]). Despite the growing numbers of papers on site-specific monitoring using a wide range of methods, it has to be stated that these methods have rarely been used in a legal context so far (probably most often in The Netherlands).

Parameters for the investigation shall be selected on the basis of (among other things) demonstrated sensitivity, cost-effectiveness, representativeness, complementarity, available local data and the possibility of determining these in a standard manner (preferably according to ISO standards). These parameters should be related to the vulnerability of the ecosystem at the test site. In addition, the collection of parameters should be evenly balanced and proportional to the size and complexity of the study site and its contamination so that an adequate complementary cover of relevant ecosystem aspects is obtained in the investigation plan for the soil quality TRIAD. An overview of available parameters is shown in Reference [59] among other places. As already mentioned, for the choice and evaluation of ecotoxicological tests, see Annex B and ISO 17616.

Pedological interpretation shall be used to refine the choice of tools for each assessment level. For example, if the soil is sandy, low in nitrogen and acidic, earthworm community tests are not the most relevant ecological tool at the ecological assessment level for habitat reasons, whereas an analysis of enchytraeid communities, for example, is possible as long as there is some organic matter associated with the sand. Another example is that bioavailability tools should be carried out as a priority in a context of metallic pollution of soil with acidic pH. Moreover, chronic bioassays on plants should be carried out with caution if a lack of nitrogen in the soils has been demonstrated.

Relevant soil properties for the selection and proper interpretation of bioassays and bioindicators are:

— soil texture (% Clay, % Silt and % Sand);

— soil pH;

— soil water holding capacity;

— soil cation exchange capacity;

— soil total organic carbon;

— soil total nitrogen;

— soil available phosphorus;

— soil available potassium.

Recommendations on compatibility of tools according to these properties may be available for some of them on Annex B.

For each of the LoEs in the soil quality TRIAD, there is a variety of analyses or tests that can be chosen (the so-called toolboxes). Lists of suitable tools (but not exhaustive) are given in Annex B, differentiated according to the TIERS of the soil quality TRIAD (see 6.4.1). The proposed TIER levels could be adapted according to specific requirements (e.g. specificities of the contaminated, sites, request from authorities…). Indeed, there are clear differences in the TRIAD approach, depending on the land use of the test site and consequently on the tools to be used.

As indicated earlier, other methods, than those listed in Annex B, can be used too (especially at higher TIERS), but when using non-standardized methods, reasons for choosing them as well as all details of their performance should be documented in detail.

NOTE 1 In case of suspected genotoxicity and others specific toxicological mechanisms (endocrine disruption, neurotoxicity, embryotoxicity…) that can affect the health and the fitness of organisms at a given site, appropriate ecotoxicological tests could be added notably those involved biomarker measurements (e.g., comet assay, enzymatic activities…).

NOTE 2 For the assessment of a site-specific soil, both the habitat function (i.e. testing organisms living in the bulk soil) as well as the retention function (i.e. testing aquatic organisms) are considered. Suitable test methods are provided in ISO 15799 (see also Reference [40]).

NOTE 3 When using chemical extraction methods and in particular models, they should have been validated using appropriate ecotoxicological data (e.g. References [5] and [32]).

TIER 1 (screening)

The first Tier of the risk assessment is a simple evaluation at screening level. The objective is to achieve a certain degree of information with minimum costs (of time and resources). “Therefore, the tools used in the first screening need not only to be reasonably quick and easy, but also relatively cheap”.

Chemistry: in the screening phase, the comparison of site-specific measured concentration with soil screening level or the calculation of the toxic pressure should expose the presence of an ecological concern. Total concentration is the conventional input data to achieve this goal but information on environmental bioavailability acquired with simple chemical extractions can turn out to be relevant. These chemicals extractions are often perceived as still quick and cheap techniques.

Ecotoxicology: the selected bioassays should be able to screen the soil samples for presence of toxic compounds, including toxic degradation compounds and chemicals that are not usually sought after. A suitable minimum response should include two ecotoxicity tests from two different trophic levels.

Ecology: in the screening phase, the ecological study should highlight a quick and first impression of the ecological structure and functioning of the soil (visible damage).

TIER 2 (refined screening)

The second Tier of the assessment can still be perceived at screening level in the sense that the needed data are relatively simple and quick to obtain. The difference is that the TIER 2 deviates from the conservatism approach to move towards a more realistic analysis of the field situation.

Chemistry: in the refined phase, the selected tools should permit a better assessment of the actual fraction of measured substances that will interact with organisms and therefore may have a negative effect. Chemical extractions are still relevant but more realistic transfer to live materials method can turn out to be more relevant.

Ecotoxicology: in the refined phase, the selected bioassays bring more information to continue to screen the soil samples for presence of toxic compounds. Living models, duration of the bioassay and adverse effect selected have to be-complementary from the ones in the screening phase. Soil species should be used essentially but aquatic bioassays conducted with soil extracts can be considered.

Ecology: in the refined phase, the ecological study still needs to highlight a quick and first impression of the ecological structure and functioning of the soil. Unlike the first level, this time we seek to highlight impacts invisible at first sight. A minimum appropriate response should cover the notion of biodiversity and that of soil function.

TIER 3 (detailed assessment)

The tools in TIER 3 differ significantly from those used in TIERS 1 and 2, as they are typically more expensive, time-consuming, and are often associated with research rather than operational contexts. However, they are intended to provide a higher level of information and contribute to a more comprehensive assessment of ecological risk at the specific site. The selection of tools in Tier 3 toolbox should be tailored to the study and based on the previous results obtained in TIERS 1 and 2.

Chemistry: In the detailed assessment, the chosen tools should allow for a precise evaluation of the actual fraction of measured substances that will interact with organisms, potentially causing adverse effects. Methods involving substance transfer to live materials are relevant, as are laboratory experiments and the use of models to account for soil aging. Additional efforts should be made to clarify the risks associated with substances identified as the most concerning in TIERS 1 and 2.

Ecotoxicology: in the detailed assessment, TIER 3 tools typically involve long-term studies focused on chronic endpoints. The selection of bioassays should be aligned with the sensitive species groups identified in TIERS 1 and 2 and may also include biomarkers to measure effects on ecosystems in a more holistic manner.

Ecology: in the detailed assessment, TIER 3 tools should aim to provide a more in-depth understanding of the impact at the population and community levels. Examining the impact on global ecosystem services, such as the soil's degradation capacity, may also be relevant.

NOTE In the UK framework, the cause–effect relationship is an integral part of the ecological risk assessment at a site to be assessed.^[25] This step has not been included in this document because it is a possible but not always necessary step of the TRIAD approach.

To decide in which TIER a tool may belong, it is possible to refer to the next table. TIER 1 tools are usually simple tools: cheap, easy to use and they can give a result in a short amount of time. TIER 2 tools are more expensive or needs more time to deliver an information or need more expertise to be used accordingly. TIER 3 tools are a step further in complexity or delivers another information to complement TIER 2.

An example for classifying tools in the different tiers is proposed below but ultimately, the position of a tool in the 3 TIERS of the TRIAD is related to expert judgement and can be considered different than in this standard if the assessor and/or authorities think it is appropriate.

Table 1 — Example of an attempt to classify different tools in the different TRIAD TIERS for each LoE.

This subclause gives an insight into some of the important decisions risk assessors have to make when conducting the soil quality TRIAD in practice, e.g. how to scale, weight and integrate the outcome of the various investigations at the individual tiers. It is based on Reference [36].

Essentially, the results from all tests should be funnelled into the risk assessment framework. To be useful for risk assessment, the outcome from all tests in a WOE approach should therefore be made comparable across the various LoEs, e.g. by a uniform scaling method. This should preferably be done without losing quantitative information.^[8][70] The primary aim is to maximize the utilization of the results of particular tests as quantitative as possible, and to use results from all tests together in a transparent and integrative scheme, e.g. in a decision matrix. Reference [8] reviewed several possibilities for disseminating final WOE findings and concluded that tabular decision matrices are the most quantitative and transparent ones. In order to derive a quantitative decision matrix for easy evaluation and integration of results from different tests in the soil quality TRIAD, it is proposed to use an effect scale running from 0 to 1, corresponding to no effect up to maximum effect. The results from each parameter (e.g. tests or ecological field survey) should be projected on this effect scale, according to best available knowledge or best professional judgments.

Different tests will obviously require different approaches. For instance, for a growth test, the percentage of inhibition can be used as the unit for effects directly. For ecological field monitoring, the results should be scaled relatively to the ecological state of the reference site (= 0) and a (theoretical) state indicating 100 % effects. Projection of test results on this effect scale requires experience and expertise. Once all results are scaled into a uniform effect value, the overall response of a set of methods, e.g. the chemical LoE, can be calculated.

A paramount issue when selecting tools for use in the soil quality TRIAD approach is the ability to scale the outcome of an assay. If the outcome of a method cannot be scaled from 0 to 1, it is not applicable in the context of the soil quality TRIAD approach presented here. However, it should, in principle, be possible to scale any tool, which has ecological relevance and ability to serve as an indicator of toxic stress, from 0 to 1. It may nevertheless sometimes need expert judgment to do so, wherefore basic knowledge of ecological risk assessment is an advantage. Scaling of results is usually not part of the description in standard guidelines. Therefore, some effort shall be given to this before initiating and conducting the studies on a case-by-case basis (detailed examples are given in Reference [36]).

Besides the issue of scaling, attention should also be paid to the issue of weighting different tests, Tiers and soil quality TRIAD LoEs. Some general principles can be put forward.

— The different LoE in the soil quality TRIAD should be equally weighted in the risk assessment, unless special considerations demand for a differential weight. The soil quality TRIAD is divided into three parts, each part has its own weaknesses and strengths. Together they form a strong starting point for the risk assessment according to the principles of a balanced WOE approach.

— Within one LoE, attention should be given to different aspects of the ecosystem. The starting point can be equal weights for all organisms and processes, applying the following statement: “all organisms are unequal, but equally important”. Another possibility is to give important ecological functions or life support functions equal weights. A balanced soil quality TRIAD approach should address all the important functions of a soil ecosystem like production, decomposition and consumption. In specific cases, differential weighting between the different LoEs in the soil quality TRIAD may be needed.

Within an individual LoE of the soil quality TRIAD, differential weighting of tests may be applied for three possible reasons.

a) First, differential weights on the end points can be applied because of ecological considerations. This differential weighting should be defined in the investigation plan and agreed on by all stakeholders. This allows extra attention to specific (functional) groups, key species, and endangered or “charismatic” species.

b) The second reason for applying differential weights is to account for the uncertainty or variability within the end points. Tests with a high level of uncertainty, or with a high variability in results, may be given a smaller weight in the ERA^[39].

c) The third reason for differential weight might correct for bias in measured and calculated effects. For instance, the geometric mean of the inverted effect value gives extra weight to those observations giving a positive response. This acknowledges the fact that many ecological field surveys are not able to demonstrate ecological effects, although, these effects are present, for instance, in highly dynamic ecosystems. In such systems, money may be too tight to collect and analyse the necessary number of replicates to demonstrate a significant effect. Reference [13] used differentiated weights in the ERA for aquatic systems following a multi-criteria decision analysis. Effects on e.g. top predators and benthos received a higher weight than parameters such as mentum deformities. This information was used to rank different sites according to their possible risk for ecosystem quality. For the terrestrial system, less experience is available. Based on this discussion,^[36] weigh the results of each test or measurement equally. However, this decision has to be made on a case-by-case basis by the respective stakeholders.

Once the results have been scaled for each test, it is possible to integrate the results of the different tests in each of the lines of evidence (LoE). Finally, the integrated results from all three LoEs are further integrated into one “risk number” of the soil quality TRIAD.^[36][44] The first integration process, i.e. within one LoE, aims to get a sufficient and complete set of information for estimating the risk of contamination. Different pieces of information are used together for this evaluation. For instance, the application of SSD adopts the reasoning that all organisms are important although they have a different sensitivity towards the contamination.^[6] Furthermore, estimates of effects based on different exposure scenarios may be used together to account for species-specific differences in bioavailability.

In the second integration step, the independent pieces of information from the three LoEs are incorporated into one number of risks. Here, it is also evaluated to what extent the three LoEs indicate the same risk, wherefore a measure of deviation between the three LoE is added. A high deviation between the results of the three LoEs could also trigger further research, as more insight is necessary to draw a final conclusion on the ERA. The major advantage of this integration method is the use of numbers, instead of the more qualitative “+” and “–” symbols used by, for example, Reference [10]. By using risk numbers instead of risk symbols, less information is lost and information about the magnitude of the risk (high effect, small effect) is given. No definite limit for acceptable risk (or deviation of risk) can be given. This may vary according to the land use of the site as well as the decisions made by stakeholders. In case of high deviation, two approaches can be taken. More research is conducted to lower the uncertainty or the high uncertainty is accepted but as a result of this, a less sensitive land use should be chosen.

Based on the results of the soil quality TRIAD investigation and the agreed assessment criteria, a decision has to be made which meets the investigation objective. This decision forms the actual result of the investigation process and is therefore set out in writing and then discussed with all the parties involved. Strictly speaking, the result of a soil quality TRIAD would be to indicate whether there is an ecological risk at a given site or not — but not to say how to handle that risk.

Quantitative uncertainties should be presented in relation to the methodology of the TRIAD expertise developed in the studies. The determination of this level of acceptable uncertainty is important for the decision to extend the investigations (with TIER 2 and TIER 3) and to strengthen the conclusion in terms of risks. The level of 0,4 that is proposed as an arbitrary example of value in^[36] is often used.^[116] This level should be decided by experts in each study in an interdisciplinary and site-specific manner. For example, for a natural site with emblematic biodiversity, low uncertainties should be tolerated in terms of risk levels, while for a simple and sparsely vegetated garden (which is very important in terms of urban ecosystem services), uncertainties could be tolerated at relatively higher levels.

NOTE 1 Depending on the investigation objective, this decision can form the basis for soil management measures, e.g. the need for a clean-up of the site or whether or not to take specific measures to reduce ecological risks.

NOTE 2 Details of this step depend highly on the national regulations and practices. So, in any case, decision-making is made in close contact with competent authorities.

The investigation report includes at least the following:

a) the following passage: “The investigation was carried out in accordance with ISO 19204”. If one or more points in this document has/have been deviated from, this is added to the above passage and the deviations are described explicitly and explained;

b) soil and site details, such as its coordinates, vegetation, land use (also its history), climate, soil properties, contamination, ecological characteristics (e.g. occurrence of protected species);

c) the stakeholder details (as a minimum: the landowner and the competent authority);

d) the investigators' (if appropriate, also consultants) details;

e) the investigation objective;

f) the results of each step in the assessment (see also Figure 1);

g) the selected assessment parameters with associated agreements about references, scales, weighting and assessment criteria;

h) a description with reasons for the investigation design (for example, by adding the investigation plan in the appendix);

i) a description of the work carried out for the soil quality TRIAD study (sampling method and numbers, chemical analyses, ecotoxicological tests, field observations);

NOTE Sampling details can be found in References [28] and [40], ISO 18400‑101, ISO 18400‑102, ISO 18400‑103, ISO 18400‑104, ISO 18400‑105, ISO 18400‑107 and ISO 18400‑206.

j) possible peculiarities or irregularities that occurred during the implementation of the investigation and an evaluation of the consequences of these for the results and conclusions;

k) results of the soil quality TRIAD study:

— all raw and unscaled investigation results (in transparent tables as much as possible);

— all the scaled results together in a transparent table (example given in Reference [60]). The effect size per soil quality TRIAD line of evidence is included after the weighting of selected parameters;

l) description of the uncertainties and the evaluation of the investigator (or consultants) as to whether the uncertainties have been insufficiently reduced in this investigation to be able to satisfy the subject of the investigation;

m) an overview of the arguments that result in the decision as to whether measures should be recommended to reduce the ecological effects (risk reduction) as part of the soil management.

The minimum requirements set for the reporting also apply to small sites and simple assessments. In the case of these sites, selections of parameters and the choice of assessment criteria are not unique and a reference to a relevant source is sufficient (for example, Reference [40]). In the case of larger or complex cases, additional requirements can be set for the reporting, such as the reasons for certain choices. A unique investigation approach and interpretation should in any case be described and the content should be justified. In the case of a non-unique approach, references to relevant sources are sufficient.

1. 
   (informative)
   
   Bioindicators of effect and accumulation — Additional tools for site-specific ecological risk assessment

Measurements of contaminants in plants, soil invertebrates and/or some vertebrates like small mammals inform on the transfer of contaminants (at least those that are not degraded in organisms) from soil to organisms and are now operational tools of site-specific risk assessment. Reference values that can be used to interpret bioaccumulation data for a site-specific risk assessment exist for plant communities, snails and small mammals (https://ecobiosoil.univ-rennes1.fr/ADEME-Bioindicateur/english/worksheet.php).

Data on bioaccumulation in organisms are also necessary to evaluate the food web transfer of contaminants that can possibly cause secondary poisoning (i.e. transfer and toxic effect of contaminants from first level of food chain to consumers belonging to higher levels^[51]; review in Reference [14]). Some models already exist to evaluate the risk of and link to secondary poisoning [for example, Berisp (Breaking Ecotoxicological Restraints In Spatial Planning) or Terrasys (http://sanexen.com/terrasys/quest-ce-que-terrasys/)]. These models need validated data on concentration of contaminants in food items belonging to the basis of food chain (primary producers, soil invertebrates). Concentrations in plants or soil invertebrates can be modelled on the basis of soil contamination. Nevertheless, when considering a particular site, the use of site-specific experimental data may improve the risk assessment and reduce the uncertainty factors that may be included at several steps of the process where using modelled data. Bioaccumulation assessment in the various animals (see review for invertebrates and vertebrates in Reference [14]) can provide important information on the bioavailability of contaminants in soils.

Measurements of bioaccumulation in plants or soil organisms are thus useful to:

— assess the effective bioavailability of contaminants in soil to organisms;

— approach the food chain transfer and the risk of secondary poisoning of consumers.

In some cases, bioaccumulation can be associated with toxic effects but this is not always the case (see ISO 17402). For example, high concentrations in earthworms or snails or plants can be well supported by these organisms but can cause cumulative exposure of and toxicity for their consumers^[33][62].

Bioaccumulation assessment can be implemented in Tier II or in Tier II and Tier III (e.g. in plants^[52] or snails^[46][48][49] or both plants and snails^[49] or small mammals (https://ecobiosoil.univ-rennes1.fr/ADEME-Bioindicateur/english/WS/WS16-Micromammals.pdf). Some site-specific studies already demonstrate the interest of using effect and bioaccumulation indicators for a site-specific risk assessment^[47][49].

1. 
   (informative)
   
   Toolboxes

The following tables contain suitable tools for the three LoE. ). Nevertheless, other tools could be used and the proposed TIER levels could be adapted according to specific requirements (e.g. specificities of the contaminated sites, request from authorities…).

Table B.1 — Chemistry LoE – Toolbox<Tbl_--></Tbl_-->

Table B.2 — Ecotoxicity LoE – Toolbox<Tbl_--></Tbl_-->

Table B.3 — LoE – Toolbox<Tbl_--></Tbl_-->

1. 
   (informative)
   
   Case studies

This annex includes two case studies to illustrate certain points of the standard through examples. These case studies correspond to research work conducted between 2015 and 2024. They do not claim to be complete applications of the standard but rather aim to shed light on specific technical aspects.

The first case study is the most comprehensive application and covers the five steps described in the standard. It is based on risk assessments conducted on contaminated soils of a former mine in France.

The second case study corresponds to the practical application of the standard (steps 3 and 4). It is based on data acquired from soils of former mines in Korea.

• 1. Case Study 1: Former Mining Site Context
     1. Context

The TRIAD approach has been applied on a former mining operation with very high metal concentrations in soils. The data comes from a research project^[1] completed in 2019. Four different zones of an ancient mine were selected, each with different characteristics such as vegetation cover and organic matter content. A reference zone, separated from the polluted area, is also part of the assessment.

This case study covers only the first and the second tier for the 4 selected soils. Uncertainty has been considered acceptable at Tier 1 for 2 soils, and the assessment went further with the second tier for the remaining two soils. At the end of the second tier, all soils exhibited high Risk Index (IR) values and acceptable uncertainties.

The case study aimed to:

— Discuss the choice of an acceptable risk interpretation framework for the study.

— Discuss the choice of an unacceptable uncertainty value beyond which the next tier must be used.

— Discuss the threshold values used to calculate toxic pressure.

— Demonstrate scaling on a tool.

— Integrate results from multiple tools to obtain a Level of Evidence (LoE) score.

— Integrate the three LoE scores in a risk index.

The standard specifies that the complete sequence of the assessment comprises 5 stages, with the Triad implementation itself corresponding to stage 4. To ensure clarity in the exercise represented by this case study, not all aspects of the study are systematically elaborated in full detail.

• • 1. First step: Objective of the investigation (formulating the problem and decision regarding the need of a site-specific risk assessment)

The entire area is contaminated with very high metal concentration, but some areas have been colonized by vegetation. There are no defined scenarios for the reuse of these soils in the future. The objective of the study is to acquire information about the polluted area and characterize the risk to the terrestrial ecosystems.

• • 1. Second step: Basic considerations

General approach:

— Ecological conditions: The studied soils have no specific uses; no specific ecological condition (such as protected species or ecosystem services) have been identified or mentioned by the land user. It is brought to the assessor's attention that the dispersion of contaminated dust is a risk vector for humans, so the presence of vegetation cover, if present, must be taken into account.

— Critical aspects of ecological conditions: There is no land use nor endangered species on the area. In the absence of particular ecological conditions that could be at risks, it is initially considered that the results of the different tools to be used will not be weighted (equal importance for all results).

Assessment criteria:

— Establishment of a measure using reference data: The results of the different tools will be scaled from 0 to 1. A value of 0 corresponds to the absence of an effect or the same value observed in the chosen reference soil. A value of 1 corresponds to 100 % effect if measurable or the furthest value from that obtained in the selected reference soil.

— Weighting factors: Initially, equal weighting of the assessment parameters within the soil quality TRIAD lines of evidence and equal weighting of the three soil quality TRIAD lines of evidence are considered.

— Agreement about reducing uncertainties in the risk assessment: The data of the case study are derived from a research project. The sampling strategy is rigorous; however, the number of samples could be criticized. Indeed, there are no triplicates, but only a single composite for each soil.

— The derivation of assessment criteria for uncertainty: The case study site is highly contaminated, and no ecological use is planned following the assessment. The primary objective is to characterize the extent of impacts on soil organisms and compare the selected soils. Therefore, the criteria for interpreting the integrated risk index and the acceptable uncertainty of the assessment are those listed in the following table.

Table C.1 — Risk index value interpretation

A value of 0 corresponds to an optimal ecological state or one corresponding to that of the unexposed reference environment to the activities of the mining site.

A value of 1 corresponds to a significant degradation of the environment's quality and biodiversity.

Table C.2 — Uncertainty value interpretation

The value of 0,4 corresponds to a default value proposed in the reference document for calculating the various indices.^[36] Given that there is no planned ecological use following the study and that the objective is rather to establish an initial assessment of the environment, it was deemed unnecessary to select a more stringent value.

It should be noted that the values presented in the two tables above are relevant proposals for this case study only and should be discussed for each TRIAD assessment, as mentioned in subclause 6.2.

• • 1. Third step: practical performance of the soil quality TRIAD (TIER 1)

The TRIAD approach is a tiered approach, TIER 1 is a screening assessment and TIER 2 and 3 having the same methodology but bringing more information at each stage. Thus, steps 3, 4, and then 5 are repeated as iteration (TIER 2 and TIER 3) until results are conclusive.

Data for the three LoEs are generated for this step. The selection of tools in the toolbox should enable the proper assessment of the soil quality.

• • • 1. Presentation of the site and sampling strategy

The selected sites exhibit characteristics suggesting differences in terms of metal concentrations and availability of the metallic compounds (vegetation cover, % organic matter).

For the three Lines of Evidence (LoE), the following tools have been selected for the TIER 1 (T1) simple screening stage.

Table C.3 — Simple screening tools

These data are simple and can be obtained quickly, aiming to provide a qualitative assessment of environmental conditions and to identify areas where ecological impact is evident.

NOTE in a real risk assessment, the individual data from selected tools are commented on if they provide relevant and supplemental information. They are not commented on in this case to maintain document clarity.

• • • 1. Chemical LoE

Table C.4 — Total concentration of metals (mg/kg)

• • • 1. Ecotoxicological LoE

Results are expressed on a 0 – 1 scale from effect percentages using the laboratory reference soil.

Table C.5 — Earthworm avoidance (ISO 17512 -1)

Table C.6 — Dehydrogenase activity of Arthrobacter globiformis (ISO 18187)

• • • 1. Ecological LoE

Table C.7 — Vegetation cover

• • • 1. Fourth step: Assessments at the different tiers: scaling, weighting and integrating results (TIER 1)
      2. Scaling
         1. Chemical LoE

Focus: in this chapter, the following points are highlighted:

— calculation of a toxic pressure;

— consideration of negative values in the scaling approach.

Scaling of the total concentration data: the toxic pressure.

The transformation of the measured data in the soil into a single index to account for the supposed effect of soil contaminants on ecosystems can be achieved with several methods. The one chosen in this case study corresponds to the calculation of the toxic pressure known as ms-PAF (multi-substance potentially Affected fraction of species) described in.^[36] It involves quantifying the combined effect of multiple chemical substances on ecological communities. The result expresses a percentage of species potentially affected at different levels defined by the toxicity threshold chosen. In accordance with this reference and given the very high concentrations observed, the HC₅₀EC₅₀^[2] are considered as this toxicity threshold instead of the HC₅₀NOEC^[3] in the subsequent calculations.

Table C.8 — Toxicity threshold (HC₅₀EC₅₀ and HC₅₀NOEC)

Toxic pressure is calculated for each contaminant on each soil using the following equation:

with

P_T toxic pressure (from 0 to 1);

HC₅₀ hazardous concentration for 50 % of species;

C_T total concentration;

slope parameter of the species sensitivity distribution (SSD), which describes the standard deviation of the collected hazard concentration data used for the SSD. The value of 0,4 is assumed as a reasonable default value for calculation of the TP.

Table C.9 — Calculated toxic pressure by component

The background concentration is taken into account by reducing the TP using the following equation:

with

PTc toxic pressure corrected with background concentration (from 0 to 1);

P_T toxic pressure (from 0 to 1);

P_Tfigure toxic pressure for reference soil (from 0 to 1).

Table C.10 — Calculated toxic pressure by component with correction for background concentrations

Because a “no risk situation” has a value of 0, negative values calculated are considered equal to 0. This situation occurs if the concentration measured in the studied soil is lower than that of the reference soil.

Note that a negative value obtained after the comparison of a reference could possibly express a better quality of the soil at the contaminated soil than the reference soil.

The last step consists in the calculation of a combined risk number with the individual corrected toxic pressure available for the n compounds measured.

Table C.11 — Toxic pressure for the TRIAD

As this is the only data for the Chemical LoE in TIER 1, these values correspond to the results of the Chemical LoE.

• • • • 1. Ecotoxicological LoE

Focus: in this chapter, the following points are highlighted:

— aggregation of results from different sources to obtain a single score for a LoE;

— consideration of impossible calculation (for example log(1-1)).

Ecotoxicological values are already expressed as percentage, there is no need for scaling. The values in Table C.5 and Table C.6 are corrected for the effect percentage observed with reference soil with the equation

with

Observed effect

Observed effect on the reference soil

Corrected value

Table C.12 — Corrected values for the bioassays results

Table C.13 — Data derived from different tools are aggregated into a single LoE score. This aggregation of values follows three steps

A result of 1 obtained with a tool cannot be considered during the aggregation of results into a single score due to the first step of the transformation (log(1-X)). Therefore, the value is changed to a value that makes the calculation possible while remaining close to 1, such as 0,99 for example.

• • • • 1. Ecological LoE

Focus: in this chapter, the following point is highlighted:

— Scaling of a result expressed in percentages with positive responses.

Ecological values are also expressed as percentages, but this time with a positive response. Since a value of 1 (100 %) corresponds to maximum risk, a transformation is necessary to exploit the information on vegetation cover.

The transformation follows two steps:

— Express the result on a scale from 0 to 1 using the following equation: (100-X)/100

— A correction compared to the result obtained on the reference site with the following equation: (X‑ ref) / (1- ref).

Table C.14 — TRIAD scaling of the vegetation cover

As these are the only data for the Ecological LoE, these values correspond to the results of the Ecological LoE.

• • • • 1. Weighting

As stated in C.1.3, equal weighting of the assessment parameters within the soil quality TRIAD lines of evidence and equal weighting of the three soil quality TRIAD lines of evidence are considered.

• • • • 1. Integration of results

Integrating results from the three Lines of Evidence is done in the same way as aggregating results from different tools (see C.1.4). The observed variance among the three scores of the three LoE provides an indication of the uncertainty surrounding the assessment at this TIER.

Table C.15 — Calculation of the TIER 1 integrated risk

Key

<graphic></graphic> Chimical Loe

<graphic></graphic> Ecotoxicological LoE

<graphic></graphic> Ecological LoE

Figure C.1 — TIER 1 result

• • 1. Fifth step: Decision on how to proceed (TIER 1)

The results are interpreted as stated in the basic considerations of the assessment C.1.3. The integrated risk indices obtained indicate “high impact on ecosystems” for "Mine tailings and Pond" soils (integrated risk index above 0,8). The uncertainty of the TIER 1 assessment for these two soils is well below the acceptable threshold and the assessment comes to its conclusion.

The uncertainty is above acceptable threshold for “Brownfield and Terraces”, it is not possible to draw a conclusion at TIER 1 and the TIER 2 implementation is required.

• • • 1. Third step: practical performance of the soil quality TRIAD (TIER 2)

The TRIAD approach is applied through a step-by-step process using tools of increasing complexity.

The following tools have been selected for the refined screening stage.

Table C.16 — TIER 2 advanced screening tools

These tools aim to provide more detailed and comprehensive data for a refined assessment of environmental conditions and ecological impacts.

The nature and number of tools depends on the assessment. The case study originates from a research project and so a lot of information is available at TIER 2; however, all data are not presented in detail to avoid making the demonstration exercise too lengthy. The results presented in detail have been selected because they illustrate a specific calculation or concept of the standard.

• • • 1. Chemical LoE

For TIER 2, the tools can provide information related to the bioavailable fraction of substances present. The following information is available:

— concentrations measured in the CaCl₂ extracts;

— concentration measured in plants grown on soils;

— SET index (ISO 24032)

Bioavailable concentrations in soil in µg/kg - extracted with CaCl2

Table C.17 — Environmental availability in soil in µg/kg (CaCl2 extraction)

Concentration of metals measured in plants sampled on site

Table C.18 — Concentration of metals in plants

SET index (ISO 24032)

Table C.19 — SET index, estimation of transfer of contaminant to land snails

• • • 1. Ecotoxicological LoE

For TIER 2, the tests provide information on chronic toxicity (growth, reproduction, etc.) of the soil on populations of organisms. The following results are available:

— Effects of contaminated soils on emergence and growth of higher plants (ISO 11269‑2) conducted on oat.

— Effects of contaminated soils on emergence and growth of higher plants (ISO 11269‑2) conducted on turnip.

— Determination of the toxic effect of sediment and soil samples on the growth, fertility, and reproduction of Caenorhabditis elegans (Nematodes) (ISO 10872).

— Determination of effects on reproduction of Eisenia fetida (ISO 11268-2).

Table C.20 — Effects of contaminated soils on emergence and growth of higher plants (ISO 11269‑2)

• • • 1. Ecological LoE

For TIER 2, ecological LoE tools provide information on biodiversity and the relationship between different populations. The available data correspond to nematode indices. They provide numerous insights into the composition of different nematode communities and the relationships between them. In this case study, it was decided to only consider the most relevant indices that can be expressed from 0 to 1 for the TRIAD approach. They are then grouped according to two different parameters:

— Nematode abundance: aggregation of indices of abundance of microbivores, phytophages, and carnivores.

— Nematode diversity: aggregation of the enrichment index, number of taxa, and Shannon index.

Table C.21 — Nematode index criteria retained for the study

• • 1. Fourth step: Assessments at the different tiers: scaling, weighting and integrating results (TIER 2)
       1. Scaling
          1. Chemical LoE

Table C.22 — Risk indices obtained by comparing extractable concentrations with PNECsoil

Table C.23 — Scaled risk index related to environmental availability of metals in soil

Metal Concentrations in Plants

The concentrations of trace elements measured in plants growing on different soils are compared to those collected at the reference site. Concentrations of arsenic, cadmium, lead, titanium, and zinc were measured, and these data are aggregated into a single value between 0 and 1 for each soil. As always, a value of 0 corresponds to the reference site, while a value of 1 corresponds to very high concentrations in the plants.

Table C.24 — Scaling of the metal concentrations in plants

The result is obtained using the Equation BKX_TRIAD with x = the absolute value of the log of the ratio [concentration in the plant at the site] / [concentration in the plant at the reference site] and n the number of substances considered.

(Jensen and Mesman 2006^[36])

In this example, the concentrations in plants are compared with one another. This is not a comparison of risk because there is no notion of toxicity involved. Another approach like calculating index risk by using threshold with ecotoxicological value (as PNECwater by example) should have been considered too.

SET Index

A value greater than 5 corresponds to a maximum risk (cf ISO 24032^[115]). The value for Terraces and brownfield are far much greater than this threshold: the transfer excess in snails is high.

Table C.25 — Scaled for TRIAD SET index

The different results from the chemical LoE tools of TIER 2 are aggregated with those from TIER 1 using the method already employed previously.

Table C.26 — Calculation of the chemical LoE effect score for TIER 2

The effect scores obtained for the Chemical LoE at TIER 2 are identical to those obtained at TIER 1. It is acknowledged that considering the bioavailability might have reduced these scores, especially for areas with vegetation and therefore organic matter, but the concentrations are very high, and the bioavailable portion remains significant.

• • • • 1. Ecotoxicological LoE

Table C.27 — Calculation of the ecotoxicological LOE effect score for TIER 2

• • • • 1. Ecological LoE

Table C.28 — Nematode index: abundance

Using the same data scaling method for the diversity index, we obtain the following values.

Table C.29 — Calculation of the ecological LoE effect score for TIER 2

• • • 1. Weighting

As stated in 7.1.3, equal weighting of the assessment parameters within the soil quality TRIAD lines of evidence and equal weighting of the three soil quality TRIAD lines of evidence are considered.

• • • 1. Integrating results

Table C.30 — TIER 2, integrated risk index and uncertainty

• • 1. Fifth step: Decision on how to proceed (TIER 2)

The integrated risk indices obtained at TIER 2 indicate “high impact on ecosystems” for "Terraces” and “Brownfield” (integrated risk index above 0,8). The uncertainty of the TIER 2 assessment for these two soils is below the acceptable threshold and the assessment can come to its conclusion.

• 1. Case study of Korea
     1. Site characterization

An abandoned mine in the Republic of Korea was selected as a case study site. Previous reports indicated that the metals, including As, Cd, Cu, and Zn, exceeded the criteria of Korean soil contamination. A village is located downstream of the study site, and high-graded ecological zone and a national park are situated within 3 km and 5 km, respectively. A large lake is also located nearby, and rainwater was observed to flow down the slope, potentially transporting pollutants into surface water and sediments.

Based on geographical indicators and previous data, four test units were selected: two mine heads (unit 1 and 2), one muck field (unit 3), and the bottom of the muck field (unit 4). The reference (R) unit was located within 350 m of study site and was selected with following criteria: 1) uncontaminated site, 2) similar soil properties to the study site, 3) similar environmental conditions including vegetation to the study site.

A conceptual site model was developed to organize the potential fate, transport, medium, exposure route, and ecological receptors of contamination (Figure C.2). Additional species were considered as ecological receptors to strengthen the Ecotoxicology-Line of Evidence (LoE). Trophic transfer was confirmed as a potential exposure route; however, it was not considered in this case study.

Figure C.2 — Conceptual site model of the study site

• • 1. Soil sampling and sample preparation

Soil sample of each unit composed of five subsamples collected from one central point and four surrounding points aligned with the cardinal directions. After removing organic matter on surface, soil was collected from a depth of 0–10 cm. Soil samples were air-dried in a greenhouse, passed through a 2 mm sieve, and then homogenized using a roller.

For ecotoxicology-LoE, 50 g of soil was mixed with 200 mL of distilled water in a triangle flask, shaken at 24 ± 1 °C and in the dark condition at 150 rpm for 24 h. The extracts were filtered twice using filter paper with pore sizes of 11 µm and 0,45 µm, respectively, and stored at 4 °C in the dark condition. All samples were adapted to room temperature before all experiments.

• • 1. TRIAD assessment
       1. Soil characterization

The soil pH in the contaminated site ranged from 4,0 to 4,5, which was lower than that of R unit (5,3 ± 0,1), except for unit 4 (7,4 ± 0,1). Electrical conductivity and cation exchange capacity for all units were generally higher in all units compared to the R. Soil texture across the units included clay loam, sandy clay loam, and loamy sand, whereas the R unit exhibited a loam texture.

• • • 1. Chemistry-LoE

The toolbox list for each LoE is shown in Table A#-1. Chemistry-LoE was determined by total concentration and three extractable concentrations using distilled water, 0,001 M CaCl₂, and 0,43 M HNO₃. No contamination was detected in the R unit, while other units had high metal concentrations, including As and Pb that exceeded the Korean environmental criteria.

The extractable concentrations with 0,43 M HNO₃ in all unit soils were much higher than those in the R soil, indicated that heavy metals were strongly adsorbed to soil particles. However, the potential for leaching was low, as lower extractable concentrations with 0,001 M CaCl₂ were found as 0–10,4 % of total concentrations. The chemistry-LoE for each unit was calculated as 1,000 for units 1–3 and 0,964 for unit 4.

• • • 1. Ecotoxicology-LoE

Ecotoxicology-LoE was estimated by six soil and six soil extract bioassays. Soil bioassays were conducted as follow: two plants, Vigna radiata, and Oryza sativa; earthworm, Eisenia andrei; collembola, Folsomia candida; soil algae, Chlorococcum infusionum; and soil nematode, Caenorhabditis elegans, and soil extract bioassays were performed as follow: water flea, Daphnia magna; fish embryo, Danio rerio; aquatic plant, Lemna minor; microorganism, Escherichia coli; nematode, Caenorhabditis elegans; and algae, Chlamydomonas reinhardtii.

Unit 1–3 soils near mine head affected the growth and survival of various species, especially in unit 3 soil, most organisms did not survive. On the other hand, unit 4 showed relatively low contamination and bioavailable metal concentrations, and some biota showed more positive responses than at unit R. Soil extract bioassays showed low toxicity, consistent with the low leachability of metals. The ecotoxicology‑LoE for each unit was determined as 0,448 (unit 1). 0,521 (unit 2), 0,989 (unit 3), and 0,048 (unit 4), respectively.

• • • 1. Ecology-LoE

Ecology-LoE was calculated based on different ecological indicators, including plant species richness, plant coverage, bait-lamina test, collembolan abundance, mite abundance, and community-level physiological profiling for soil microorganisms.

Overall, soil contamination at units 1–3 had negative impacts on the ecosystem functions of various biological communities, including reduced vegetation, decreased soil biological activity, and changes in microbial function. Unit 3 exhibited the lowest vegetation cover and species diversity, while soil fauna activity and abundance declined significantly in units 1 and 2. In contrast, microbial activity was high in unit 4, which is interpreted as an adaptive or resistant response to heavy metals. The ecology-LoE for each unit was estimated as 0,655 (unit 1). 0,752 (unit 2), 0,532 (unit 3), and 0,276 (unit 4), respectively.

Table C.31 — Toolbox lists for three lines of evidence
(chemistry-LoE, ecotoxicology-LoE, and ecology-LoE)

• • • 1. Integrated Risk (IR)

The IR value was estimated based on three LoEs with equal weightage and risk categories were defined as follows: no risk (0,00 ≤ IR ≤ 0,25), low risk (0,25 < IR ≤ 0,50), moderate risk (0,50 < IR ≤ 0,75), and high risk (0,75 < IR ≤ 1, 00).

The IR values were 0,701 (unit 1), 0,758 (unit 2), 0,840 (unit 3), and 0,429 (unit 4), respectively (Table C.32 and Figure C.3). Units 1–3 showed moderate to high risk, required remediation action due to high possibility of surrounding outflow by pollution erosion. Unit 4 had low risk, though with higher uncertainty due to a standard deviation greater than 0,4.

Table C.32 — Three lines of evidence (LoE) and integrated risk

Figure C.3 — Triangle charts for Integrated Risk (IR) values for each unit, derived from three lines of evidence (LoEs); chemistry-LoE (Chem-LoE), ecotoxicology-LoE (Ecotox-LoE), and ecology-LoE (Eco-LoE). Unit R represents a reference site as control site

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[78] ISO 11063, Soil quality — Direct extraction of soil DNA

[79] ISO 11074, Soil quality — Vocabulary

[80] ISO 11267, Soil quality — Inhibition of reproduction of Collembola (Folsomia candida) by soil contaminants

[81] ISO 11268‑2, Soil quality — Effects of pollutants on earthworms — Part 2: Determination of effects on reproduction of Eisenia fetida/Eisenia andrei and other earthworm species

[82] ISO 11269‑2, Soil quality — Determination of the effects of pollutants on soil flora — Part 2: Effects of contaminated soil on the emergence and early growth of higher plants

[83] ISO 11348‑3, Water quality — Determination of the inhibitory effect of water samples on the light emission of Vibrio fischeri (Luminescent bacteria test) — Part 3: Method using freeze-dried bacteria

[84] ISO 13829, Water quality — Determination of the genotoxicity of water and waste water using the umu-test

[85] ISO 14238, Soil quality — Biological methods — Determination of nitrogen mineralization and nitrification in soils and the influence of chemicals on these processes

[86] ISO 15799, Soil quality — Guidance on the ecotoxicological characterization of soils and soil materials

[87] ISO 16387, Soil quality — Effects of contaminants on Enchytraeidae (Enchytraeus sp.) — Determination of effects on reproduction

[88] ISO 17126, Soil quality — Determination of the effects of pollutants on soil flora — Screening test for emergence of lettuce seedlings (Lactuca sativa L.)

[89] ISO 17155, Soil quality — Determination of abundance and activity of soil microflora using respiration curves

[90] ISO 17402, Soil quality — Requirements and guidance for the selection and application of methods for the assessment of bioavailability of contaminants in soil and soil materials

[91] ISO 17512‑1, Soil quality — Avoidance test for determining the quality of soils and effects of chemicals on behaviour — Part 1: Test with earthworms (Eisenia fetida and Eisenia andrei)

[92] ISO 17512‑2, Soil quality — Avoidance test for determining the quality of soils and effects of chemicals on behaviour — Part 2: Test with collembolans (Folsomia candida)

[93] ISO 17601, Soil quality — Estimation of abundance of selected microbial gene sequences by quantitative polymerase chain reaction (qPCR) from DNA directly extracted from soil

[94] ISO 17616, Soil quality — Guidance on the choice and evaluation of bioassays for ecotoxicological characterization of soils and soil materials

[95] ISO 18187, Soil quality — Contact test for solid samples using the dehydrogenase activity of Arthrobacter globiformis

[96] ISO 18311, Soil quality — Method for testing effects of soil contaminants on the feeding activity of soil dwelling organisms — Bait-lamina test

[97] ISO 18400‑101, Soil quality — Sampling — Part 101: Framework for the preparation and application of a sampling plan

[98] ISO 18400‑102, Soil quality — Sampling — Part 102: Selection and application of sampling techniques

[99] ISO 18400‑103, Soil quality — Sampling — Part 103: Safety

[100] ISO 18400‑104, Soil quality — Sampling — Part 104: Strategies

[101] ISO 18400‑105, Soil quality — Sampling — Part 105: Packaging, transport, storage and preservation of samples

[102] ISO 18400‑107, Soil quality — Sampling — Part 107: Recording and reporting

[103] ISO 18400‑206, Soil quality — Sampling — Part 206: Collection, handling and storage of soil under aerobic conditions for the assessment of microbiological processes, biomass and diversity in the laboratory

[104] ISO 18772, Soil quality — Guidance on leaching procedures for subsequent chemical and ecotoxicological testing of soils and soil materials

[105] ISO 22030, Soil quality — Biological methods — Chronic toxicity in higher plants

[106] ISO 23611‑1, Soil quality — Sampling of soil invertebrates — Part 1: Hand-sorting and extraction of earthworms

[107] ISO 23611‑2, Soil quality — Sampling of soil invertebrates — Part 2: Sampling and extraction of micro-arthropods (Collembola and Acarina)

[108] ISO 23611‑3, Soil quality — Sampling of soil invertebrates — Part 3: Sampling and extraction of enchytraeids

[109] ISO 23611‑4, Soil quality — Sampling of soil invertebrates — Part 4: Sampling, extraction and identification of soil-inhabiting nematodes

[110] ISO 23611‑5, Soil quality — Sampling of soil invertebrates — Part 5: Sampling and extraction of soil macro-invertebrates

[111] ISO 23611‑6, Soil quality — Sampling of soil invertebrates — Part 6: Guidance for the design of sampling programmes with soil invertebrates

[112] ISO/TS 29843‑1, Soil quality — Determination of soil microbial diversity — Part 1: Method by phospholipid fatty acid analysis (PLFA) and phospholipid ether lipids (PLEL) analysis

[113] ISO/TS 29843‑2, Soil quality — Determination of soil microbial diversity — Part 2: Method by phospholipid fatty acid analysis (PLFA) using the simple PLFA extraction method

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[115] ISO 24032, Soil quality — In situ caging of snails to assess bioaccumulation of contaminants

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1. The Triple project (2016 - 2019) "TRIAD method for the risk assessment for ecosystems - application on a workshop site," is a French research project funded by ADEME (French Environment and Energy Management Agency). It aims to use data obtained from a former mine site, mainly polluted by trace metals, to gain experience in applying the TRIAD method. (www.ademe.fr/mediatheque Nicolas Pucheux, Lucie Roux, Sandrine Andres, Pascal Pandard, Eric Thybaud, INERIS, ADEME. 2017. Rapport final – Retour d'expérience par étude de cas sur un ancien site minier (méthode TRIADE pour l’évaluation du risque pour les écosystèmes). 52p. ↑

2. The HC₅₀EC₅₀ (Hazardous Concentration for 50 % of species based on EC₅₀) is a statistical measure used in ecotoxicology to estimate the concentration of a substance at which 50 % of species in an ecological community show significant adverse effects. ↑

3. The HC₅₀NOEC (Hazardous Concentration for 50 % of species based on No Observed Effect Concentrations) is a statistical measure to estimate the concentration of a substance at which 50 % of species in an ecological community show no observable adverse effects. ↑