Methodology for Deriving Standards
for Contaminants in Soil
to Protect Human Health

This report may be cited as:

Ministry for the Environment. 2011. Methodology for Deriving Standards for Contaminants in Soil to Protect Human Health. Wellington: Ministry for the Environment.

Published in June 2011 by the
Ministry for the Environment
Manatū Mō Te Taiao
PO Box 10362, Wellington 6143, New Zealand

ISBN:978-0-478-37237-3

Publication number: ME 1055

Other publications in this series include:
Toxicological Intake Values for Priority Contaminants in Soil

© Crown copyright New Zealand 2011

This document is available on the Ministry for the Environment’s website:

Acknowledgements

This report was prepared for the Ministry for the Environment by Graeme Proffitt (Pattle Delamore Partners Limited).The sections of the report relating to plant bioconcentration factors for each contaminant, and produce consumption (Appendix 3), were derived from reports prepared by Jo-Anne Cavanagh (Landcare Research).

The advice and assistance of the Ministry’s Technical Advisory Group for this report is acknowledged.The members were:

Gerald Rys – Ministry of Agriculture and Forestry

Jim Waters – Environmental Risk Management Authority New Zealand

John Reeves – New Zealand Food Safety Authority

Marcus Hermann – Auckland City Council

Martin Robertson – Shell Oil

Mervyn Chetty – Auckland City Council

Murray Parrish – Carter Holt Harvey

Natalia Foronda – Ministry of Health

Nick Kim – Environment Waikato

Contents

Acknowledgements

Executive Summary

1Introduction

1.1Background

1.2Purpose

1.3Document organisation

2General Approach to Deriving Soil Guideline Values

2.1Concepts in risk assessment

2.2Generic equations

2.3Generic exposure scenarios

3Exposure Scenarios

3.1Scenarios adopted

3.2Scenarios not adopted

4Derivation Equations

4.1General

4.2Background exposure

4.3SGV(health) derivation equations for each pathway

4.4Soil ingestion

4.5Dermal absorption

4.6Produce ingestion

4.7Inhalation

5Exposure Parameters

5.1General

5.2Degree of conservatism

5.3General exposure parameters

5.4Pathway-specific parameters

5.5Contaminant-specific factors

5.6Summary of exposure factors

6Soil Contaminant Standards for Selected Priority Contaminants

6.1Arsenic

6.2Boron

6.3Cadmium

6.4Chromium

6.5Copper

6.6Inorganic lead

6.7Inorganic mercury

6.8Benzo(a)pyrene (BaP)

6.9DDT

6.10Dieldrin

6.11Dioxin and dioxin-like PCBs

6.12Pentachlorophenol

7Summary of Soil Contaminant Standards and Guideline Values

8Limitations of Soil Contaminant Standards

9Site-specific Risk Assessment

9.1Purpose

9.2Introduction

9.3When a site-specific assessment should not be carried out

9.4When a site-specific assessment must be carried out

9.5When a site-specific assessment may be carried out

9.6What factors may be changed?

9.7The site-specific assessment process

Appendices

Appendix 1:Detailed Calculations

Appendix 2:Detailed SGV(health) Calculations for Cadmium

Appendix 3:Determination of the Amount of Produce Consumed and its Dry Weight

Appendix 4:Dioxin SGV(health) Calculations with Egg Consumption

Appendix 5:International Comparison of Soil Guideline Value Derivation

Appendix 6:Natural Background Topsoil Datasets for Arsenic and Cadmium

Abbreviations and Glossary

References

Tables

Table ES1:Summary of soil contaminant standards – SCSs(health) – for inorganic substances (mg/kg)

Table ES2:Summary of soil contaminant standards – SCSs(health) – for organic compounds (mg/kg1)

Table 1:Scenarios for generic numeric values in various jurisdictions

Table 2:Parks / recreation scenarios – recommended approaches

Table 3:Age ranges and body weights of receptors considered in national and international derivation protocols

Table 4:Comparison of daily soil intake for recreational scenarios

Table 5:Soil ingestion rates used in national and international protocols

Table 6:Summary of child soil ingestion rate recommendations as reviewed

Table 7:Default soil ingestion rates for child and adult (mg/day)

Table 8:Produce consumption rates (g FW/day) used in international protocols

Table 9:Default produce consumption rates: weights in grams with percentage of total vegetables given in parenthesis

Table 10:Area of exposed skin and body parts considered to be exposed for different receptors, used in national and international protocols

Table 11:Body parts exposed for a child and associated skin areas (cm2)

Table12:Estimated soil adherence factors (mg/cm2)

Table13:Soil adherence values (mg/cm2)

Table 14:Summary of daily inhalation rates in existing New Zealand and international guidelines (m3/day)

Table 15:Inhalation rates recommended in Exposure Factors Handbook

Table 16:General and scenario-specific exposure parameters

Table 17:BCF for arsenic from different sources

Table 18:Contaminant-specific parameters for the derivation of the arsenic soil contaminant standard

Table 19:Arsenic soil contaminant standard (mg/kg)

Table 20:Contaminant-specific parameters for the derivation of the boron soil contaminant standard

Table 21:Boron soil contaminant standard (mg/kg)

Table 22:Coefficients determined for equations 23 and 24, and the percentage of the variability in the data

Table 23:Coefficients determined for equation 24, and the percentage of the variability in the data explained using an extended data set

Table 24:Contaminant-specific parameters for the derivation of the cadmium soil contaminant standard

Table 25:Cadmium soil contaminant standard (mg/kg)

Table 26:Summary of BCFs for chromium from different sources

Table 27:Contaminant-specific parameters for the derivation of the chromium soil contaminant standard

Table 28:Chromium III soil contaminant standard (mg/kg)

Table 29:Chromium VI soil contaminant standard (mg/kg)

Table 30:Contaminant-specific parameters for the derivation of the copper soil contaminant standard

Table 31:Copper soil contaminant standard (mg/kg)

Table 32:Recommended BCF (dry weight) and BCF (dry weight) for lead from different sources

Table 33:Contaminant-specific parameters for the derivation of the lead soil contaminant standard

Table 34:Lead soil contaminant standard (mg/kg)

Table 35:BCF for mercury from different sources

Table 36:Contaminant-specific parameters for the derivation of the inorganic mercury soil contaminant standard

Table 37:Inorganic mercury soil contaminant standard (mg/kg)

Table 38:Contaminant-specific parameters for the derivation of the BaP soil contaminant standard

Table 39:BaP soil contaminant standard (mg/kg)

Table 40:PEFs for use in assessing potential carcinogenicity of PAH mixtures

Table 41:BCF (geometric mean) for p,p’-DDT and p,p’-DDE in root and leafy vegetables determined from the literature

Table 42:Contaminant-specific parameters for the derivation of the DDT soil contaminant standard

Table 43: DDT soil contaminant standard (mg/kg)

Table 44:Contaminant-specific parameters for the derivation of the dieldrin soil contaminant standard

Table 45: Dieldrin soil contaminant standard (mg/kg)

Table 46:WHO (2005) TEFs for dioxins and dioxin-like PCBs

Table 47:BCF for dioxins and dioxin-like PCBs from Inui et al (2008), Hulster et al (1994) and recommended BCFs

Table 48:Contaminant-specific parameters for derivation of the dioxin and dioxin-like soil contaminant standards

Table 49:Dioxin and dioxin-like PCB soil contaminant standards (µg TEQ/kg)

Table 50:Egg lipid / soil ratios for PCDD/PCDFs and dioxin-like PCBs

Table 51:Dioxin and dioxin-like PCB soil guideline values for egg consumption pathway (µg TEQ/kg)

Table 52:Contaminant-specific parameters for the derivation of the PCP soil contaminant standard

Table 53:PCP soil contaminant standard (mg/kg)

Table 54:Summary of soil contaminant standards (shaded) and guideline values for inorganic substances (unshaded) (mg/kg)

Table 55:Summary of soil contaminant standards (shaded) and guideline values for organic compounds (unshaded)

Table 56:Modifiable exposure factors, typical situations and examples

Table A1.1:General and scenario-specific exposure parameters

Table A3.1:Amount of fruit and vegetables consumed (grams per day) by different age-gender groups based on simulated diets for the New Zealand 2003/04 Total Diet Surveys

Table A3.2:Vegetables considered in simulated diets, and their grouping

Table A3.3:Fresh to dry conversion factors for vegetables

Table A3.4:Amounts of different vegetable groups consumed by an average adult and average child, with percentage of total vegetables given in parenthesis

Table A5.1:Summary of the name / terminology used, purpose, and basis for derivation of soil guideline values in different countries

Table A5.2:Summary of USEPA exposure pathways of concern for residential and commercial / industrial land uses, and construction for deriving SSLs

Table A5.3:Exposure scenarios in existing New Zealand industry-based guidelines

Table A6.1:Regional council supplied data

Table A6.2:National statistics of the natural arsenic background concentration in topsoil

Table A6.3:Statistics of the natural arsenic background concentration in topsoil by region

Table A6.4:Summary statistics of the national natural background cadmium topsoil dataset

Table A6.5:Arsenic background sites in native bush

Table A6.6:Cadmium background sites

Figures

Figure 1:Pathway for subsurface vapour intrusion into indoor air

Figure 2:Life expectancy at birth, 1876–2002

Figure 3:Variation in plant bioconcentration factors (BCF, dry weight) for leafy vegetables with soil concentration and pH

Figure 4:Variation in plant bioconcentration factors (BCF, dry weight) for root and tuber vegetables with soil concentration and pH

Figure 5:Dependence of cadmium soil contaminant standard on pH

Figure 6:Site-specific assessment steps

Figure A2.1:Dependence of cadmium soil guideline value on pH

Figure A5.1:Derivation of screening values based on different risk levels and applications

Figure A5.2:Overview of steps for derivation of a soil quality guideline in Canada

Figure A5.3:Assumed soil allocation factor from the residual tolerable daily intake

Figure A5.4:Schematic lay-out of the CSOIL exposure model

Executive Summary

This technical report sets out a risk-based methodology for deriving soil contaminant concentrations protective of human health. Together with the Toxicological Intake Values for Priority Contaminants in Soil(MfE, 2011),this document serves as a technical referencein support of the National Environmental Standard for Assessing and Managing Contaminants in Soilto Protect Human Healthand should be read in conjunction with it (see

This report addresses a question that is fundamental to the science of contaminated land management: What contaminant concentration in soil can people be exposed to and yet not be subject to an appreciable risk of harm?The answer to this question varies internationally because each jurisdiction frames its response to fit within unique risk policy and legislative frameworks. So, although the technical approach to risk assessment of contaminated land is shared broadly by most countries, there are significant differences in detail such that a standard adopted by one country may not suit another.

As an alternative to adopting standards from another country, the Ministry for the Environment has examined the science of risk assessment and compiled a derivation methodology for health-based standards to apply to soil contaminants in New Zealand under the Resource Management Act 1991. This initiative comes at a time when it is appropriate also to review the soil guideline values contained within the Ministry’s existing suite of contaminated land guidelines. The ‘soil contaminantstandards’contained in this technical report are intended to supersede the ‘soil acceptance criteria’ used in previous New Zealand guidelines; the new methodology also resolves technical differences between them.The Ministry intends to apply the same approach when reviewing the petroleum hydrocarbon contaminants.

The term ‘soil contaminant standards’ to protect human health, or SCSs(health),specifically refers to soil contaminant concentrations that are mandatory, under the National Environmental Standard for Assessing and Managing Contaminants in Soilto Protect Human Health. SCSs(health)may be applied as Tier 1 or screening criteria; as conservative clean-up targets, to inform on-site management actions; or to trigger further investigation within a Tier 2 assessment. When talking about generic numerical values in guidelines or foreign jurisdictions, or for soil contaminant concentrations that are derived on a site-specific basis according to this methodology, the term soil guideline values (SGVs) is used.

If SCSs(health)or SGVs(health) are exceeded, it may result in health effects that are more than minor for some people, and as such are unacceptable.Conversely, if actual soil concentrations are less than or equal to the SCSs(health) or SGVs(health)then this is judged to be acceptable, because any adverse effects on human health for most people are likely to be no more than minor.

The methodology in this document is government policy and has two applications. First it demonstrates how the standards for contaminants in soil were derived for use within the NES regulation as ‘soil contaminant standards’, SCSs(health). Secondly, it sets out the basis for deriving soil contaminant concentrations protective of human health for exposure scenarios that lie outside of the generic exposure scenarios under the NES. The purpose of this second application of the methodology is to guide the site-specific derivation of soil guideline values, SSGVs(health), when there is good reason to use a site-specific risk assessment.

It is important to note that the methodology and the derived standards are intended to be protective of human health only, and do not apply to other environmental receptors.When it is relevant to protect other valued elements of the environment, separate consideration of appropriate values to achieve this is required.

This report presents:

  • a national risk-based methodology for deriving soil contaminant concentrations protective of human health
  • a suite of numerical criteria for priority contaminants that are legally binding as gazetted under the National Environmental Standard for Assessing and Managing Contaminants in Soilto Protect Human Health
  • background information on the risk assessment methodologies and exposure parameters.

SCSs(health)are derived for the following priority contaminants:arsenic, boron, cadmium, chromium, copper, inorganic lead, inorganic mercury (but not elemental mercury), benzo(a)pyrene (representing the carcinogenic polycyclic aromatic hydrocarbons), DDT (as the sum of DDT, DDD and DDE), dieldrin, dioxin (as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and dioxin-like polychlorinated biphenyls (PCBs)), and pentachlorophenol (PCP).

The SCS(health)calculations draw on toxicological intake values and background exposures set out in the companion document,Toxicological Intake Values for Priority Contaminants in Soil(MfE, 2011).Numerical values are calculated for five generic land-use scenarios, and utilise standardised receptors and exposure parameters.

A summary of the SCSs(health) derived is presented in Tables ES1 and ES2.Contaminated-land practitioners are referred to the more detailed version of these tables set out in section 7 of this report, in which additional residential sub-scenarios have also been derived.

Table ES1:Summary of soil contaminantstandards– SCSs(health)– for inorganic substances (mg/kg)

Arsenic / Boron / Cadmium (pH 5)1 / Chromium / Copper / Inorganiclead / Inorganic mercury
III2 / VI
Rural residential / lifestyle block 25% produce / 17 / NL / 0.8 / NL / 290 / NL / 160 / 200
Residential 10% produce / 20 / NL / 3 / NL / 460 / NL / 210 / 310
High-density residential / 45 / NL / 230 / NL / 1,500 / NL / 500 / 1,000
Recreation / 80 / NL / 400 / NL / 2,700 / NL / 880 / 1,800
Commercial / industrial outdoor worker / 70 / NL / 1,300 / NL / 6,300 / NL / 3,300 / 4,200

1Default value is for pH 5. Values increase with increasing pH (see Appendix 2).

2The SCSs(health) for boron, chromium III and copper represent levels well in excess of concentrations that would affect the health of plants.

NL = No limit. This is where the derived values exceed 10,000 mg/kg.

Table ES2:Summary of soil contaminantstandards– SCSs(health)– for organic compounds (mg/kg1)

Scenario / BaP / DDT / Dieldrin / PCP / Dioxin (µg/kg TEQ)
TCDD / Dioxin-like PCBs
Rural residential / lifestyle block 25% produce / 6 / 45 / 1.1 / 55 / 0.12 / 0.09
Residential 10% produce / 10 / 70 / 2.6 / 55 / 0.15 / 0.12
High-density residential / 24 / 240 / 45 / 110 / 0.35 / 0.33
Recreation / 40 / 400 / 70 / 150 / 0.6 / 0.52
Commercial / industrial outdoor worker / 35 / 1,000 / 160 / 360 / 1.4 / 1.2

1All values in mg/kg dry weight except dioxins which are in µg/kg.

Methodology for Deriving Standards for Contaminants in Soil to Protect Human Health1

1Introduction

1.1Background

The Ministry for the Environment (MfE) has determined the need for a better policy framework for managing contaminated land in New Zealand.After extensive public consultation, the Ministry published a position paper in September 2007 (MfE, 2007).The paper identified, among other things, an inconsistent and variable use by contaminated-land practitioners of numerical contaminatedland guidelines used to assess the risk that contaminated soil might pose to human health.The Ministry then determined that, as a matter of priority, it would develop:

  • a national risk-based methodology for deriving soil contaminant concentrations protective of human health
  • a suite of numerical criteria for priority contaminants as examples of the national methodology
  • site management options and actions that follow from applying the above criteria; ie, the numerical criteria may:

serve as Tier 1 or screening criteria to assess whether there is a potential risk to human health

when the numerical criteria are exceeded, serve as conservative clean-up targets for many situations, ie, where further investigation or site-specific risk assessment is not warranted or economic

inform on-site management actions to reduce the potential for adverse effects

trigger further investigation to better assess the risk and/or determine site-specific criteria as a Tier 2 assessment.

The Ministry intends that the derivation methodology be incorporated by reference into the National Environmental Standard for Assessing and Managing Contaminants in Soilto Protect Human Health (NES), as was proposed in the Discussion Document (Proposed National Environmental Standard for Assessing and Managing Contaminants in Soil, MfE, 2010a).While the technical detail behind the newly derived soil contaminantstandards is presented within this separate methodology document, the soil contaminantstandards will be applied in accordance with the NES and within the context of the derivation methodology.

This technical report introduces and sets out the risk-based methodology the Ministry has adopted as government policy for deriving SCSs(health): soil contaminantstandardsto protect human health.SCSs(health) are derived for a limited group of priority contaminants that are of primary concern in New Zealand. These are specifically: arsenic, boron, cadmium, chromium, copper, inorganic lead, inorganic mercury, benzo(a)pyrene, DDT, dieldrin, pentachlorophenol, and dioxin (as 2,3,7,8-tetrachlorodibenzo-p-dioxin, and dioxin-like polychlorinated biphenyls). These calculations draw on toxicological values and background exposures set out in a companion document Toxicological Intake Values for Priority Contaminants in Soil (MfE, 2011).

The numerical values are restricted to consideration of human-health risks and are based on conservative standard land-use scenarios, using standardised receptors and exposure parameters.