Treating sheep with an external chemical insecticide for economic and welfare reasons has been universal farming practice in New Zealand since the 19th century, and was in fact a requirement under various Acts of Parliament. Approaches have evolved from dipping animals in a chemical bath (a "sheep dip") through to the modern preferred pour-on methods. As a result, across New Zealand it is estimated that thousands of former sheep-dip sites exist on both public and private land. Their numbers and locations are largely unknown.
Old sheep-dip sites are defined for the purposes of this guideline as those in operation prior to 1980 and subsequently disused. They are typically contaminated due to the historical use of persistent and toxic chemicals, including arsenic, dieldrin, DDT, [1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane.] aldrin and lindane. [Gammexane is the commercial name for formulations based on purified γ-hexachlorocyclohexane, also known as lindane. Note that BHC refers to a mix of different isomers of hexachlorocyclohexanes.] Exposure to these chemicals may cause harm to humans, animals and the ecosystem. Potential risks arise through contact with contaminated soils, groundwater or surface water; eating food grown in or on contaminated soil; or eating animals that have ingested contaminated soil. This guideline has been developed by the Ministry for the Environment to help local authorities address the potential risks to human health and the environment from exposure to contaminants associated with sheep dips.
Many areas in New Zealand previously used for pastoral farming are now being developed into more intensive cropping, horticultural, dairying and residential land uses. These changes in land use are due partly to an increased demand for high-value crops and horticulture, and partly to the continued growth and spread of urban centres. However, the change in land use of sites previously used for sheep-dipping activities raises the risk for contaminant exposure to people. Development activities can also increase the migration of any residual contaminants from a site.
Throughout New Zealand, and worldwide, management of the chemicals used to treat animals for external parasites has improved. Modern insecticides are hazardous at the time of use, but they usually degrade readily in the environment. The potential risk to consumers, handlers and the environment has decreased accordingly. This guideline therefore focuses on the problems resulting from the historical use of environmentally persistent dipping chemicals.
Due to the likely presence of sheep dips in pastoral areas, it is important that local authorities [For the purposes of this guideline, the term "local authorities" refers to the territorial authorities (ie, city and district councils), unitary authorities and regional councils.] and district health boards are aware of the risk these contamination "hot spots" may pose to human health and the environment. The guideline provides best practice advice on how to identify potentially contaminated sheep-dip sites, and how to determine the level of contamination that is acceptable for various land uses. They also provide recommended practical site management and remediation options.
The main purpose of the guideline is to provide local authorities with practical guidance on:
- locating former sheep-dip sites
- assessing risks to human health and to the environment
- evaluating remediation and long-term management options.
The guideline presents the entire process − from sheep-dip identification and investigation, to site remediation or management − in a logical flow. A number of case studies highlight the highly variable nature of sheep-dip sites, and different scenarios illustrate practical remediation and management options, depending on the proposed land use and the extent of contamination.
Recent amendments to the Resource Management Act 1991 (RMA) have specified the functions of local authorities for managing contaminated land. The New Zealand Waste Strategy (Ministry for the Environment, 2002) includes targets for contaminated sites that reflect the importance of improving contaminated sites management and reporting at the local level. This guideline is intended to be used both by territorial authorities for land-use planning and by regional councils for the management of contaminated sites and the protection of human health and the environment. These two functions combine to ensure that land is suitable for its specified use, and to avoid an unacceptable risk to people and the environment.
In addition to these functions, a council may have a direct interest in this guideline as an owner of public land on which sheep-dipping activity has taken place. Under section 17 of the RMA, every person has a duty to avoid, remedy or mitigate adverse effects on the environment. This means that landowners (public and private) may be responsible for identifying sheep dips on their properties. The guideline should therefore be useful for landowners in general and other interested parties, including property developers, surveyors and consultants. Good cooperation between landowners and their councils in the process of identifying, investigating and remediating sheep-dip sites is strongly advised.
In addition to using this guideline, local authorities are encouraged to raise awareness among landowners. This could be done by a series of practical guidelines that address the potential risks to children who live on farms, occupational exposure of landowners/ occupiers or remediators, livestock exposure, or contaminant residues in produce. A best practice approach for each landowner would be to record accurate information about the location of old dipping sites and any risk mitigation measures undertaken so that this information can be passed on to the next landowner.
The guideline addresses three target groups, as follows.
Figure 1: Target groups and the related key sections of the guideline
The key section for territorial authorities is the Planner’s Guide, Section 2 and Appendix 2.
The key section for regional councils is on guideline values in Section 5 and Appendix 6.
The key section for landowners is on guideline values in Section 6 and Appendix 6 and on remediation and management options in Section 6 and Appendix 1.
A local authority would ideally follow the proposed procedures in the Planner's Guide while taking into account the specific circumstances of a site. Not all sections in the guideline may be relevant to a particular situation, and sometimes simple management options can be applied.
Parts of the guideline particularly relevant to local authorities are:
- section 3, which describes a process that takes the user through a sequence of checking for the presence of sheep dips, assessing the risks of those identified, and ensuring the risks are adequately managed
- Figure 5, which contains a flow chart that local authorities may want to incorporate in their resource consent application process
- Appendix 1, which contains a checklist local authorities may want to supply to private landowners who are preparing their resource consent application and suspect that an old sheep dip might be on their property
- Appendix 2, which contains a draft district plan provision that can be used by territorial or unitary authorities as a template to incorporate into their district plans to provide for the management of sheep dips and the potential health risks arising from those sites.
In total, the guideline comprises seven sections, as follows.
- Introduction - the purpose and structure of the guideline
- Characteristics of sheep-dip contamination - sheep-dip practices, patterns of contamination, chemicals of concern, exposure pathways and risks
- Planners' guide - a flow chart and checklist, plus guidance on information management for local authorities (especially relevant to resource consent applications)
- Identifying former sheep-dip sites - practices and techniques to gather information on the presence of old sheep-dip sites
- Site investigation - sampling and analysis, assessment of results and reporting
- Site remediation and risk management - various options for managing the risks from, or remediating, former sheep-dip sites
- Best practice tips for common sheep-dip scenarios - examples of possible approaches by local government to different situations.