Developing soil guideline values to protect terrestrial biota (Eco-SGVs)
Soil guideline values developed to protect terrestrial biota (soil microbes, invertebrates, plants, wildlife and livestock) (Eco-SGVs) provide a useful means for assessing potential environmental impact of contaminants. The absence of national Eco-SGVs has resulted in inconsistency and a lack of focus to ensure protection of terrestrial biota from contaminant impacts through territorial and regional/unitary council functions. An Envirolink Tools Project was initiated to address this gap. Specifically, the project established agreed methods for developing Eco-SGVs, and developed values for the most commonly encountered contaminants, and outlined their intended application.
An advisory group of representatives from the Regional Waste and Contaminated Land Forum, Land Monitoring Forum, Land Managers Group, the Ministry for the Environment, and the Ministry for Primary Industries oversaw the project. The advisory group confirmed the range of receptors to be considered in the development of Eco-SGVs (Fig. 1), and the contaminants for which Eco-SGVs were derived.
Eleven priority contaminants that have different physico-chemical properties, and thus behaviour in the environment, were selected: arsenic, boron, cadmium, chromium, copper, fluorine, lead, zinc, DDT, total petroleum hydrocarbons, and polycyclic aromatic hydrocarbons. These included the most common contaminants identified at contaminated sites, as well as contaminants for which toxicity to livestock (fluorine) or bioaccumulation in wildlife (DDT) need also to be considered.
Eco-SGVs are developed by collation and analysis of toxicity data for individual contaminants. The values for Eco-SGVs are influenced by decisions made about the toxicity data used and the level of environmental protection intended to be afforded by the Eco-SGVs. These decisions are often more a matter of policy and consensus rather than science, and should take into account the intended application of the Eco-SGVs. As such a series of workshops with regional council staff, organic waste sector representatives and contaminated land practitioners were held to provide input to the development of the methodology.
The ‘added-risk’ approach was used to derive Eco-SGVs for trace elements. This considers that the availability of the background concentrations of a contaminant is zero or sufficiently close that it makes no practical difference, and that it is the added anthropogenic amounts that are of primary consideration for toxicity considerations. Eco-SGVs are thus developed by adding the contaminant limit developed by analysis of toxicity data (referred to as the added contaminant limit, ACL) to the background concentration. Thus regional variations in background concentrations are taken into account.
Determination of background concentrations as described in Cavanagh et al. (2015) is based on the premise that background soil concentrations are predominantly influenced by the underlying geology. The background concentrations are naturally occurring levels, which differ from ambient concentrations that arise from diffuse or non-point sources by general anthropogenic activity but not attributed to industrial or commercial land use. These can also be used to develop Eco-SGVs. Currently there are insufficient data to robustly determine ambient concentrations of contaminants of concern across New Zealand. The predicted background concentrations are available at https://lris.scinfo.org.nz/layer/48470-pbc-predicted-background-soil-concentrations-new-zealand/.
The ACLs were developed through review of toxicity data, using species sensitivity distributions (SSDs) where sufficient data were available. This enables the selection of different levels of protection. A summary of the level of protection provided for different land-use classes is shown in Table 1. Where possible, contaminant aging was taken into account, and also contaminant limits developed for sensitive, typical, and tolerant soils, based on basic soil properties (pH, carbon content, cation-exchange capacity).
Table 1. Summary of land use categories, receptors covered, and level of protection of plants, soil processes, and invertebrates for Eco-SGVs
|Level of protection (%)1|
|Plants||Soil processes/ invertebrates|
|Commercial /Industrial||Soil microbes, plants, invertebrates||60 (65)||60 (65)|
|Residential and recreational areas||Soil microbes, plants, invertebrates, wildlife||80 (85)||80 (85)|
|Agriculture, including pasture, horticulture and cropping||Soil microbes, plants, invertebrates, wildlife and livestock||95 (99)||802 (85)|
|Non-food production land||Soil microbes, plants, invertebrates, wildlife||95 (99)||95 (99)|
|Ecologically sensitive areas||Soil microbes, plants, invertebrates, wildlife||99||99|
The proposed application of Eco-SGVs was developed through workshops with regional councils and serves two purposes; assisting with contaminated land management and protecting soil quality (Table 2).
Table 2. Proposed application of Eco-SGVs for each land-use category and purpose
Contaminated land management
Protection of Soil quality
Inform remediation standards1 –specifically the quality of any soil imported onto site |
Trigger further site investigation, including off-site effects, in the event of significant exceedance2
|Residential and recreational areas||
Identification of contaminated land
|Consent limits for application of wastes (e.g. biosolids, cleanfill, managed fill) to land|
|Agriculture||As above3||As above|
|Non-food production land||As above3||As above|
|Ecologically sensitive areas||As above3||As above|
1 noting that Eco-SGVs for copper and zinc, in particular, should not automatically be applied as remediation standards – the effect of excavation and disposal of soil should be considered relative to the effect of actively managing the land to reduce concentrations over time.
2 >2 times the Eco-SGV over an area of 25 m2
3 Typically for small areas of contamination such as sheep dips, spray sheds.
na – not applicable
The Eco-SGVs developed through the Tools Project are currently being adopted in an ad hoc manner by different councils. To facilitate consistent use of the background concentrations and Eco-SGVs determined in this project nationally, three key next steps are recommended:
- International peer review of the derivation methodology for the Eco-SGVs, taking into account the intended applications.
- Wider consultation with regional councils, industry groups (e.g. contaminated land practitioners, waste industry, organic waste sector), and other stakeholders on the currently proposed application for background soil concentrations and Eco-SGVs. The latter would ensure complementarity and consistency with other sector developed guidelines, including Technical Guidelines for Disposal to Land (WasteMinz 2016), and with guidelines for the beneficial use of organic waste (under development at the time of completion of the Tools Project).
- The development of national policy or standards for the protection of soil quality and for contaminated land management that is inclusive of protection of terrestrial biota.
JO CAVANAGH, KIRAN MUNIR
Manaaki Whenua – Landcare Research
For further reading see:
Cavanagh JE 2016. User Guide: Background soil concentrations and soil guideline values for the protection of ecological receptors (Eco-SGVs) – Consultation draft. Landcare Research Report for Envirolink Tools Grant C09X1402.
Cavanagh JE, Munir K 2016. Development of soil guideline values for the protection of ecological receptors (Eco-SGVs): Technical document. Landcare Research Report for Envirolink Tools Grant C09X1402.
Cavanagh JE, McNeil S, Arienti C, Rattenbury 2015. Background soil concentrations of selected trace elements and organic contaminants in New Zealand. Landcare Research Report 2440 for Envirolink Tools Grant C09X1402.
All available at: http://www.envirolink.govt.nz/envirolink-tools/land-and-soil-tools/