ISO 16751:2020

Soil quality — Environmental availability of non-polar organic compounds — Determination of the potentially bioavailable fraction and the non-bioavailable fraction using a strong adsorbent or complexing agent

This document specifies an extraction method to determine the bioavailable (potential and environmental available) fraction and the non-bioavailable fraction of a contaminant in soil using a "receiver phase" for an organic contaminant with strong sorbing or complexing properties, for example, Tenax®[1] or cyclodextrin, respectively. NOTE 1 The bioavailable fraction is defined in ISO 17402 as environmental bioavailability. The method is applicable for non-polar organic contaminants with an aqueous solubility of NOTE 2 The method is theoretically applicable to non-polar organic contaminants with an aqueous solubility of 1 000 mg/l. The method has been often applied for compounds with a much lower solubility (Kow > 3) and less for compounds with a higher solubility. The applicability is therefore defined for compounds with an aqueous solubility of [1] Tenax® is an example of a suitable product available commercially. This information is given for the convenience of users of this document and does not constitute an endorsement by ISO of this product.

Qualité du sol — Disponibilité environnementale des composés organiques non polaires — Détermination de la fraction potentiellement biodisponible et de la fraction non biodisponible en utilisant un agent adsorbant fort ou un agent complexant

General Information

• Status: Published
• Publication Date: 25-Jun-2020
• ICS: 13.080.30 - Biological properties of soils
• Technical Committee: ISO/TC 190/SC 7 - Impact assessment
• Drafting Committee: ISO/TC 190/SC 7/WG 6 - Transfer and mobility of components
• Current Stage: 9020 - International Standard under periodical review
• Start Date: 15-Apr-2025
• Completion Date: 15-Apr-2025

Relations

• Revises: ISO/TS 16751:2018 - Soil quality — Environmental availability of non-polar organic compounds — Determination of the potential bioavailable fraction and the non-bioavailable fraction using a strong adsorbent or complexing agent
• Effective Date: 23-Apr-2020

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 16751
First edition
Soil quality — Environmental
availability of non-polar organic
compounds — Determination of the
potentially bioavailable fraction and
the non-bioavailable fraction using a
strong adsorbent or complexing agent
Qualité du sol — Disponibilité environnementale des composés
organiques non polaires — Détermination de la fraction
potentiellement biodisponible et de la fraction non biodisponible en
utilisant un agent adsorbant fort ou un agent complexant
PROOF/ÉPREUVE
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 3
6 Apparatus . 3
7 Procedure. 4
7.1 Sample preparation . 4
7.2 Determining water content . 5
7.3 Method A: Cyclodextrin . 5
7.3.1 Extraction of the sample . 5
7.3.2 Phase separation . 5
7.3.3 Extraction from receiver phase . 5
7.4 Method B: Tenax® . 5
7.4.1 Extraction of the sample . 5
7.4.2 Phase separation . 6
7.4.3 Extraction from receiver phase . 6
7.5 Measurement . 7
7.5.1 Potential bioavailable fraction . 7
7.5.2 Non-bioavailable fraction . 7
7.6 Blank test . 7
8 Calculation . 7
8.1 Potential bioavailable fraction . 7
8.2 Non-bioavailable fraction . 8
9 Expression of results . 8
10 Validation . 9
11 Test report . 9 ®
Annex A (informative) Preparation and regeneration of Tenax .10
Annex B (informative) Illustrations.11
Annex C (informative) Validation study results .14
Bibliography .25
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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 7, Soil
and site assessment.
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.
iv PROOF/ÉPREUVE © ISO 2020 – All rights reserved

Introduction
The solubility of most non-polar organic contaminants is limited and they are sorbed to the soil
matrix. They may desorb and become available for organisms, which may result in an effect (toxicity,
degradation or bioaccumulation). Not all sorbed (adsorbed and absorbed) contaminants will desorb
and become available.
Extractions used in chemical analysis to measure the total concentration, release more contaminants
from the soil than are available. It is however also possible that contaminants are so strongly bounded
by the soil that they will not be released by chemical extraction. This strong sorption may also be
caused by incorporation of the contaminant (or a degradation or reaction product of the contaminant)
in the organic soil structure. The distribution of contaminants over sorption sites of varying sorption
strength is not constant in time and contaminants will shift, with increasing contact time, to the
stronger sorption sites.
Figure 1 shows schematically the differentiation between:
— extractable residues that are also bioavailable (i.e. the potentially bioavailable fraction);
— residues that are extractable by harsher extraction methods but are non-bioavailable;
— residues that are neither extractable nor bioavailable.
If a degradable substance enters a soil, part of it will degrade over time (curve a). The area between
curve a and c is extractable by exhaustive chemical procedures. For risk assessments, this part is
considered as the “total concentration” for which values are defined in many regulations. However,
only a part of this amount is bioavailable. The area between curves a and b is the bioavailable fraction
and the area between curves b and c is the non-bioavailable fraction. The method described in this
document enables the measurement of the potential bioavailable and the non-bioavailable fraction of a
contaminant in soil.
Key
X time
Y contaminant concentration
1 degradable
2 bioavailable
3 extractable, non-bioavailable
4 non-extractable: persistent residues
5 non-available fraction
NOTE For curves a, b and c see description in text above.
Figure 1 — Temporal changes in extractable/bioavailable fractions, extractable/non-
bioavailable fractions and non-extractable/non-bioavailable fractions of a non-polar organic
contaminant (modified from [1])
In the scientific research to bioavailability a large number of definitions and concepts are in use, which
reflect the discussion in the scientific world. However, a more clear and simple approach is necessary.
In regulation, organic contaminants are either bioavailable or non-bioavailable. To support decisions,
both should be measurable. Therefore, this document follows the approach of Ortega-Calvo et al. (2015)
[2]
as illustrated in Figure 2. In this approach all defined fractions are measurable as further explained
in Clause 4.
vi PROOF/ÉPREUVE © ISO 2020 – All rights reserved

Figure 2 — Measurement of bioavailability of organic chemicals: a simplified scheme for use in
[9]
regulation
The colour boxes at the left of the biological membrane represent the distribution of pollutant molecules
among four classes (non-extractable, very slowly/slowly desorbing, rapidly desorbing and water-
dissolved) in soils and sediments. In the scheme in Figure 2, the bioavailable chemical is represented
by the rapidly desorbing and dissolved concentrations. The chemical methods able to measure the
pollutant present in each specific fraction are given in the grey boxes. The green box to the right of
the cell membrane represents the processes that occur within the organism exposed to the pollutant.
These biological processes can also serve as the basis for standard methods used for bioavailability
measurements.
As presented in Figure 2, the bioavailable fraction can be measured using the method described in this
document.
INTERNATIONAL STANDARD ISO 16751:2020(E)
Soil quality — Environmental availability of non-polar
organic compounds — Determination of the potentially
bioavailable fraction and the non-bioavailable fraction
us
...

INTERNATIONAL ISO
STANDARD 16751
First edition
2020-06
Soil quality — Environmental
availability of non-polar organic
compounds — Determination of the
potentially bioavailable fraction and
the non-bioavailable fraction using a
strong adsorbent or complexing agent
Qualité du sol — Disponibilité environnementale des composés
organiques non polaires — Détermination de la fraction
potentiellement biodisponible et de la fraction non biodisponible en
utilisant un agent adsorbant fort ou un agent complexant
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 3
6 Apparatus . 3
7 Procedure. 4
7.1 Sample preparation . 4
7.2 Determining water content . 5
7.3 Method A: Cyclodextrin . 5
7.3.1 Extraction of the sample . 5
7.3.2 Phase separation . 5
7.3.3 Extraction from receiver phase . 5
7.4 Method B: Tenax® . 5
7.4.1 Extraction of the sample . 5
7.4.2 Phase separation . 6
7.4.3 Extraction from receiver phase . 6
7.5 Measurement . 7
7.5.1 Potential bioavailable fraction . 7
7.5.2 Non-bioavailable fraction . 7
7.6 Blank test . 7
8 Calculation . 7
8.1 Potential bioavailable fraction . 7
8.2 Non-bioavailable fraction . 8
9 Expression of results . 8
10 Validation . 9
11 Test report . 9 ®
Annex A (informative) Preparation and regeneration of Tenax .10
Annex B (informative) Illustrations.11
Annex C (informative) Validation study results .14
Bibliography .25
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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 7, Soil
and site assessment.
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.
iv © ISO 2020 – All rights reserved

Introduction
The solubility of most non-polar organic contaminants is limited and they are sorbed to the soil
matrix. They may desorb and become available for organisms, which may result in an effect (toxicity,
degradation or bioaccumulation). Not all sorbed (adsorbed and absorbed) contaminants will desorb
and become available.
Extractions used in chemical analysis to measure the total concentration, release more contaminants
from the soil than are available. It is however also possible that contaminants are so strongly bounded
by the soil that they will not be released by chemical extraction. This strong sorption may also be
caused by incorporation of the contaminant (or a degradation or reaction product of the contaminant)
in the organic soil structure. The distribution of contaminants over sorption sites of varying sorption
strength is not constant in time and contaminants will shift, with increasing contact time, to the
stronger sorption sites.
Figure 1 shows schematically the differentiation between:
— extractable residues that are also bioavailable (i.e. the potentially bioavailable fraction);
— residues that are extractable by harsher extraction methods but are non-bioavailable;
— residues that are neither extractable nor bioavailable.
If a degradable substance enters a soil, part of it will degrade over time (curve a). The area between
curve a and c is extractable by exhaustive chemical procedures. For risk assessments, this part is
considered as the “total concentration” for which values are defined in many regulations. However,
only a part of this amount is bioavailable. The area between curves a and b is the bioavailable fraction
and the area between curves b and c is the non-bioavailable fraction. The method described in this
document enables the measurement of the potential bioavailable and the non-bioavailable fraction of a
contaminant in soil.
Key
X time
Y contaminant concentration
1 degradable
2 bioavailable
3 extractable, non-bioavailable
4 non-extractable: persistent residues
5 non-available fraction
NOTE  For curves a, b and c see description in text above.
Figure 1 — Temporal changes in extractable/bioavailable fractions, extractable/non-
bioavailable fractions and non-extractable/non-bioavailable fractions of a non-polar organic
contaminant (modified from [1])
In the scientific research to bioavailability a large number of definitions and concepts are in use, which
reflect the discussion in the scientific world. However, a more clear and simple approach is necessary.
In regulation, organic contaminants are either bioavailable or non-bioavailable. To support decisions,
both should be measurable. Therefore, this document follows the approach of Ortega-Calvo et al. (2015)
[2]
as illustrated in Figure 2. In this approach all defined fractions are measurable as further explained
in Clause 4.
vi © ISO 2020 – All rights reserved

Figure 2 — Measurement of bioavailability of organic chemicals: a simplified scheme for use in
[9]
regulation
The colour boxes at the left of the biological membrane represent the distribution of pollutant molecules
among four classes (non-extractable, very slowly/slowly desorbing, rapidly desorbing and water-
dissolved) in soils and sediments. In the scheme in Figure 2, the bioavailable chemical is represented
by the rapidly desorbing and dissolved concentrations. The chemical methods able to measure the
pollutant present in each specific fraction are given in the grey boxes. The green box to the right of
the cell membrane represents the processes that occur within the organism exposed to the pollutant.
These biological processes can also serve as the basis for standard methods used for bioavailability
measurements.
As presented in Figure 2, the bioavailable fraction can be measured using the method described in this
document.
INTERNATIONAL STANDARD ISO 16751:2020(E)
Soil quality — Environmental availability of non-polar
organic compounds — Determination of the potentially
bioavailable fraction and the non-bioavailable fraction
using a strong adsorbent or complexing agent
1 Scope
This document specifies an extraction method to deter
...

INTERNATIONAL ISO
STANDARD 16751
First edition
2020-06
Soil quality — Environmental
availability of non-polar organic
compounds — Determination of the
potentially bioavailable fraction and
the non-bioavailable fraction using a
strong adsorbent or complexing agent
Qualité du sol — Disponibilité environnementale des composés
organiques non polaires — Détermination de la fraction
potentiellement biodisponible et de la fraction non biodisponible en
utilisant un agent adsorbant fort ou un agent complexant
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 3
6 Apparatus . 3
7 Procedure. 4
7.1 Sample preparation . 4
7.2 Determining water content . 5
7.3 Method A: Cyclodextrin . 5
7.3.1 Extraction of the sample . 5
7.3.2 Phase separation . 5
7.3.3 Extraction from receiver phase . 5
7.4 Method B: Tenax® . 5
7.4.1 Extraction of the sample . 5
7.4.2 Phase separation . 6
7.4.3 Extraction from receiver phase . 6
7.5 Measurement . 7
7.5.1 Potential bioavailable fraction . 7
7.5.2 Non-bioavailable fraction . 7
7.6 Blank test . 7
8 Calculation . 7
8.1 Potential bioavailable fraction . 7
8.2 Non-bioavailable fraction . 8
9 Expression of results . 8
10 Validation . 9
11 Test report . 9 ®
Annex A (informative) Preparation and regeneration of Tenax .10
Annex B (informative) Illustrations.11
Annex C (informative) Validation study results .14
Bibliography .25
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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 7, Soil
and site assessment.
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.
iv © ISO 2020 – All rights reserved

Introduction
The solubility of most non-polar organic contaminants is limited and they are sorbed to the soil
matrix. They may desorb and become available for organisms, which may result in an effect (toxicity,
degradation or bioaccumulation). Not all sorbed (adsorbed and absorbed) contaminants will desorb
and become available.
Extractions used in chemical analysis to measure the total concentration, release more contaminants
from the soil than are available. It is however also possible that contaminants are so strongly bounded
by the soil that they will not be released by chemical extraction. This strong sorption may also be
caused by incorporation of the contaminant (or a degradation or reaction product of the contaminant)
in the organic soil structure. The distribution of contaminants over sorption sites of varying sorption
strength is not constant in time and contaminants will shift, with increasing contact time, to the
stronger sorption sites.
Figure 1 shows schematically the differentiation between:
— extractable residues that are also bioavailable (i.e. the potentially bioavailable fraction);
— residues that are extractable by harsher extraction methods but are non-bioavailable;
— residues that are neither extractable nor bioavailable.
If a degradable substance enters a soil, part of it will degrade over time (curve a). The area between
curve a and c is extractable by exhaustive chemical procedures. For risk assessments, this part is
considered as the “total concentration” for which values are defined in many regulations. However,
only a part of this amount is bioavailable. The area between curves a and b is the bioavailable fraction
and the area between curves b and c is the non-bioavailable fraction. The method described in this
document enables the measurement of the potential bioavailable and the non-bioavailable fraction of a
contaminant in soil.
Key
X time
Y contaminant concentration
1 degradable
2 bioavailable
3 extractable, non-bioavailable
4 non-extractable: persistent residues
5 non-available fraction
NOTE  For curves a, b and c see description in text above.
Figure 1 — Temporal changes in extractable/bioavailable fractions, extractable/non-
bioavailable fractions and non-extractable/non-bioavailable fractions of a non-polar organic
contaminant (modified from [1])
In the scientific research to bioavailability a large number of definitions and concepts are in use, which
reflect the discussion in the scientific world. However, a more clear and simple approach is necessary.
In regulation, organic contaminants are either bioavailable or non-bioavailable. To support decisions,
both should be measurable. Therefore, this document follows the approach of Ortega-Calvo et al. (2015)
[2]
as illustrated in Figure 2. In this approach all defined fractions are measurable as further explained
in Clause 4.
vi © ISO 2020 – All rights reserved

Figure 2 — Measurement of bioavailability of organic chemicals: a simplified scheme for use in
[9]
regulation
The colour boxes at the left of the biological membrane represent the distribution of pollutant molecules
among four classes (non-extractable, very slowly/slowly desorbing, rapidly desorbing and water-
dissolved) in soils and sediments. In the scheme in Figure 2, the bioavailable chemical is represented
by the rapidly desorbing and dissolved concentrations. The chemical methods able to measure the
pollutant present in each specific fraction are given in the grey boxes. The green box to the right of
the cell membrane represents the processes that occur within the organism exposed to the pollutant.
These biological processes can also serve as the basis for standard methods used for bioavailability
measurements.
As presented in Figure 2, the bioavailable fraction can be measured using the method described in this
document.
INTERNATIONAL STANDARD ISO 16751:2020(E)
Soil quality — Environmental availability of non-polar
organic compounds — Determination of the potentially
bioavailable fraction and the non-bioavailable fraction
using a strong adsorbent or complexing agent
1 Scope
This document specifies an extraction method to deter
...