In section 4 we established a hierarchy for applying the guideline values for contaminated sites that are given in various New Zealand and international documents. Before applying the hierarchy, however, it is important to understand the principles that govern the application of these environmental guideline values, and to understand the factors that can influence their applicability. Doing so should ensure that the guideline values used in contaminated site assessment and management are chosen appropriately.
The following discussion establishes some principles for applying the hierarchy, and provides alternative information sources if guideline values are not available in the EGV database.
5.1 Principles of application
The hierarchy established in section 4 should be applied in keeping with the following principles.
In the Resource Management Act 1991, "sustainable management" means managing the use, development, and protection of natural and physical resources in a way, or at a rate, which enables people and communities to provide for their social, economic, and cultural wellbeing and for their health and safety (RMA 1991, section 2). Therefore, guideline values should be applied to contaminated sites that are appropriate for the site itself and the likely use of the site. For example, an industrial site that is to be rezoned as parkland should be remediated or managed to ensure that parkland criteria are met - not industrial criteria. Similarly, it is important to consider all receptors (human and ecological) on and near a site.
There are a large number of environmental guideline values available internationally for the assessment of contaminated sites. The guideline values and documents referenced in this document and provided in the EGV database are those identified by contaminated site practitioners in New Zealand at the time of writing as being the most commonly used, or are significant documents to which attention should be drawn.
If no New Zealand guideline value is available, there are three approaches that can be used to select a value from an international source.
- the lowest (most conservative) appropriate guideline value is used, or
- the user presents all the international guideline values identified, but selects one for use and justifies why that particular value has been chosen, or
- none of the available criteria are used and a site-specific risk assessment is undertaken according to the derivation methodology (Ministry for the Environment, 2011), see also sections 5.3.1 and 5.3.3 for further information.
While there are an increasing number of reference documents available, occasionally a guideline value may not be available for a particular contaminant. In this situation it is also appropriate to undertake a site-specific risk assessment.
5.2 Factors for consideration
It is important to note that no value represented in the EGV database should be taken and arbitrarily applied to a site without considering the following factors.
5.2.1 Background contaminant concentrations
The identification and use of data about background concentrations is necessary in any contaminated site assessment to see if any contaminants present are the result of anthropogenic activities, and to allow a reasoned assessment of risk. Background concentrations of contaminants will vary widely from area to area, depending on soil type, geology and other factors. Ideally, the background concentrations of contaminants in the area under investigation should be determined for each investigation. However, where this is not feasible, the following documents are available:
- Methodology for Deriving Standards for Contaminants in Soil to Protect Human Health Appendix 6: Natural Background Topsoil Datasets for Arsenic and Cadmium, (Ministry for the Environment, 2011)
- Background Levels of Agrichemical Residues in Bay Of Plenty Soils A preliminary technical investigation (Prepared by SEM NZ Limited, March 2005)
- Historic Pesticide Residues in Horticultural and Grazing Soils in the Tasman District (SK Gaw, June 2003)
- Assessment of Background Concentrations of Selected Determinands in Canterbury Soils (Canterbury Regional Council, 1996)
- Trace Element Concentrations in Soils and Soil Amendments from the Auckland Region (Auckland Regional Council, 1999)
- Background Concentrations of Inorganic Elements in Soils from the Auckland Region (Auckland Regional Council, 2001)
- Determination of Common Pollutant Background Concentrations for the Wellington Region DRAFT (URS New Zealand Ltd for Greater Wellington, July 2003).
These documents contain background concentrations of inorganic contaminants in soil in selected areas of New Zealand. Documents such as these that detail contaminant concentrations in environmental media relevant to the area being evaluated can also be used in assessing whether contaminant concentrations detected are above background concentrations and require further investigation.
Additionally, while organochlorine contaminants such as organochlorine pesticides and dioxins are generally not considered to be naturally occurring (although some natural sources for dioxins exist), they are often present in the environment at low levels due to atmospheric transport. The following documents provide an indication of ambient concentrations of organochlorines in soil, rivers, and estuaries in New Zealand.
- Ambient concentrations of selected organochlorines in soil (Buckland et al, 1998a)
- Ambient concentrations of selected organochlorines in rivers (Buckland et al, 1998b)
- Ambient concentrations of selected organochlorines in estuaries (Scobie et al, 1999).
Some environmental consultants and analytical laboratories may also hold information about background concentrations of contaminants in the environment.
5.2.2 Ecological receptors
To provide protection for natural resources, ecological receptors on or near a site should be considered. The majority of the documents referenced in this guideline and provided in the EGV database consider either effects on humans or ecological effects. The Canadian and Dutch soil guideline values are the only ones that are based on protection of both humans and ecological receptors, although guideline values in New Zealand documents incorporate protection of on-site ecosystems to the extent necessary to facilitate the use of the land (ie, plant growth and livestock). The basis for deriving guideline values (which ones take into account ecological end-points) is provided in section 3. Where appropriate values are not available, an ecological risk assessment should be conducted (see section 5.3.3).
5.2.3 Site-specific conditions
Not all sites investigated will conform to the assumptions or parameters used in the derivation of the guideline value (ie, pathways/receptors). There are also likely to be things that are not addressed in the derivation of the criteria, such as sensitive populations, or unusual site characteristics. These factors should be identified during the development and application of a conceptual site model and, where necessary, a site-specific risk assessment should be undertaken or an alternative guideline value selected and justified.
5.2.4 Cumulative effects of multiple contaminants
'Cumulative effect' can be used to describe the additive or synergistic effect of multiple contaminants at a site, or as a result of more than one site releasing contaminants into the same receiving environment.
There is much debate about the extent and nature of cumulative effects, and how they can be most effectively investigated, monitored, and managed on any given site. It is beyond the scope of this document to discuss these, apart from commenting that the majority of criteria given in the EGV database have been derived from a single chemical dose/response assumption. Therefore, where there are combinations of chemicals or exposures, attention should be paid to the increased or decreased effects these chemicals have in combination as opposed to individually.
Users should seek advice from toxicologists on specific issues, as necessary.
5.3 When no guideline value is available
When no appropriate guideline value or concentration for the contaminant source/pathway/ exposure scenario being evaluated can be found in the EGV database or other reference document published internationally, it may be appropriate and cost-effective to develop a site-specific guideline value, as follows.
5.3.1 Human health
An appropriate methodology to develop a site-specific guideline value is outlined in the derivation Methodology (Ministry for the Environment, 2011). Users should familiarise themselves with this document and/or seek specialised technical advice prior to undertaking this development.
The process of developing site-specific risk-based guideline values simply utilises more detailed and less generic information in the assessment process, and is explained in various levels of detail in a variety of documents (eg, Ministry for the Environment, 1997, 1999, 2011).
The general steps in the Methodology used in establishing risk-based guideline values for humans is described below (modified from Ministry for the Environment and Ministry of Health, 1997):
- a preliminary assessment of the chemicals of concern based on reported concentrations at the site and safety data
- identification of exposure paths for humans
- estimation of the likely human exposure to each chemical of concern for significant exposure routes, within the limits described in the Methodology (Ministry for the Environment, 2011)
- estimation of the effects of human exposure from available animal, occupational health, and epidemiological data
- derivation of contaminant soil concentrations that are considered not to pose an unacceptable risk to human health.
The US Department of Energy-sponsored Risk Assessment Information System provides an online system to select guideline values and can be accessed at http://rais.ornl.gov.
Users must ensure that the assumptions used in these models are appropriate for the site under consideration and acceptable to all parties involved.
5.3.2 Drinking water
Where water is used as a drinking-water source and no guideline value (referred to as a maximum acceptable value, or MAV) is given in the Drinking-water Standards for New Zealand 2005 (Revised 2008) (Ministry of Health, 2008), the following documents should be consulted:
- Australian Drinking Water Guidelines (NHMRC/ARMCANZ, 1996)
- Guidelines for Drinking-water Quality (WHO, 1993 and addenda 1998).
If neither of these documents provide any clarification or guidance on appropriate guideline values, the local medical officer of health should be contacted and appropriate advice sought.
5.3.3 Ecological risk assessment
Ecological risk assessment (ERA) focuses on the impacts from contaminants on non-human receptors, including both flora and fauna in terrestrial and aquatic ecosystems and encompassing microbes, invertebrates, and vertebrates. Ecological risk assessment is growing in research and regulatory application internationally. Information that has a specific New Zealand focus and includes general information on ecological risk assessment is available at: www.landcareresearch.co.nz.
This website aims to help environmental risk managers to make informed ecological risk assessments at contaminated sites and to derive New Zealand-specific environmental tolerance levels in soil, groundwater, and surface water for key contaminants.