|dc.description.abstract||Sheep dipping was a historic agricultural practice where sheep were immersed into insecticides to eradicate external parasites. Historical use of pesticides has caused localised soil contamination at former sheep dipping sites. There is limited information on offsite contamination such as in stream sediments, groundwater, and surface water. Predominant contaminants at historic sheep dipping sites are arsenic (As) and organochlorine (OC) compounds. There are estimated to be 50,000 former sheep dip sites in New Zealand, of which, over 10,000 are estimated to be in the Waikato Region. Contamination at historical sheep dip sites is potentially concerning for human and environmental health.
The objectives of this study were to (1) evaluate a range of historic sheep dips to identify sites that had the highest leaching potential; (2) characterise the selected study sites; (3) establish the extent of contamination in soil, sediments, and water; (4) evaluate the extent of offsite contamination; and (5) assess compliance to environmental guideline limits.
Soil samples from two former sheep dip sites were analysed for arsenic, copper, and organochlorines at depths of up to 20 cm. Further soil samples were analysed for arsenic at depths of up to 7.5 cm. Stream water and sediment samples were analysed for arsenic, copper, and organochlorines at upstream, downstream, and discharge point of a dip site located on a flood zone. Arsenic (0 - 2,839 mg/kg), dieldrin (0 - 8.60 mg/kg), lindane (including by-products) (0 - 0.560 mg/kg), DDT (including metabolites) (0 - 1.200 mg/kg), and endrin (0 - 0.127 mg/kg) were the main contaminants detected in soil samples. Concentrations of As (0.9 - 32 mg/kg), dieldrin (0 - 0.038 mg/kg), and benzene hexachloride (α-BHC and β-BHC) (0 - 0.0031 mg/kg) were detected in stream sediments. Organochlorine was not detected in surface water. As in surface water ranged from 0 to 0.0021 g/m3, which was well below the maximum acceptable value (MAV) of 0.01 g/m3for potable drinking water supplies.
Arsenic concentrations in 142 soil samples were well above environmental guidelines for human habitation (30 mg/kg). Dieldrin recorded low to moderate contamination in soils with one sample exceeding the environmental guideline of 6 mg/kg. Arsenic in 4 of the 18 stream sediment samples were above the interim sediment quality low level guideline (ISQG-Low) of 20 mg/kg. Dieldrin concentrations in surface sediments up to 13 cm deep were well above the interim sediment quality high level guideline (ISQG-High) of 0.008 mg/kg. α-BHC and β-BHC had no ISQG guideline. The levels detected were above the lindane guideline (ISQG-High) of 0.001 mg/kg in surface sediments. Evidence of sheep dip chemicals moving away from a sheep dip site included arsenic, dieldrin, and DDT up to 100 m downhill from a dip site located on the margins of a steep slope with an adjacent gully. Elevated As was detected in stream sediments up to 40 m downstream of a dip site located on a flood zone. High level contamination from dieldrin, α-BHC, and β-BHC were recorded in downstream sediments.
This study recommends that sheep dips located within 15 m of a stream and margins of steep slopes with an adjacent gully should be regarded as priority sites for contaminated land investigations that should include a monitoring programme.||