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Executive Summary
This technical report sets out a risk-based methodology for deriving soil contaminant concentrations protective of human health. Together with the Draft Toxicological Intake Values for Priority Contaminants in Soil (MfE, 2010b), this document serves as a technical reference in support of the Proposed National Environmental Standard for Assessing and Managing Contaminants in Soil: Discussion Document (Ministry for the Environment, 2010a), and should be read in conjunction with it.
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 soil guideline derivation methodology for application 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 guideline values for human health, SGVs(health) 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 SGVs(health) specifically refers to a soil contaminant concentration that, if exceeded, may result in health effects that are more than minor for some people, such an exceedance being unacceptable. Conversely, if actual soil concentrations are less than or equal to the 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. SGVs(health) have been calculated for five generic land-use exposure scenarios to illustrate firstly their method of derivation and secondly, to show how they can be applied in practice. It is important to note that these values are intended to be protective of human health only, and not 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 draft numerical criteria for priority contaminants as examples of the national methodology
- background information on the risk assessment methodologies and exposure parameters.
As outlined in the accompanying proposed national environmental standard discussion document (MfE, 2010a), the SGVs(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.
Draft SGVs(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) and dioxin-like polychlorinated biphenyls (PCBs), and pentachlorophenol. The SGV(health) calculations draw on toxicological intake values and background exposures set out in the companion document Draft Toxicological Intake Values for Contaminants in Soil: Technical Report (MfE, 2010b).Numerical values are calculated for a generic suite of land-use scenarios, and utilise standardised receptors and exposure parameters.
A summary of the SGVs(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 subscenarios have also been derived.
Table ES1: Summary of soil guideline values for inorganic substances (mg/kg)
| Arsenic | Boron | Cadmium (pH 5)1 | Chromium | Copper | Inorganic lead | Inorganic mercury | ||
|---|---|---|---|---|---|---|---|---|
| III2 | VI | |||||||
| Rural residential / lifestyle block 10% produce | 20 | 34,000 | 5 | 280,000 | 560 | 32,000 | 730 | 380 |
| Residential 10% produce | 24 | 34,000 | 5 | 280,000 | 560 | 32,000 | 730 | 380 |
| High-density residential | 50 | 75,000 | 370 | 890,000 | 1,800 | 60,000 | 1,600 | 1,200 |
| Recreation | 100 | 220,000 | 1,100 | NL | 5,200 | 170,000 | 4,700 | 3,500 |
| Commercial / industrial outdoor worker | 70 | 400,000 | 1,600 | NL | 6,300 | 290,000 | 7,000 | 4,200 |
1 Default value is for pH 5.
2 The SGVs(health) for boron, chromium III and copper represent levels well in excess of concentrations that would affect the health of plants.
NL = No limit
Table ES2: Summary of soil guideline values for organic compounds (mg/kg1)
Scenario |
BaP |
DDT |
Dieldrin |
PCP |
Dioxin (µg/kg TEQ) |
|
|---|---|---|---|---|---|---|
TCDD |
Dioxin-like PCBs |
|||||
| Rural residential / lifestyle block 10% produce | 85 | 90 | 3.1 | 70 | 0.19 | 0.15 |
| Residential 10% produce | 100 | 90 | 3.1 | 70 | 0.19 | 0.15 |
| High-density residential | 240 | 270 | 50 | 130 | 0.41 | 0.38 |
| Recreation | 440 | 750 | 110 | 230 | 1.1 | 0.9 |
| Commercial / industrial outdoor worker | 300 | 1,000 | 160 | 360 | 1.4 | 1.2 |
1 All values in mg/kg dry weight except dioxins which are in µg/kg.
