Historical sheep dip sites are potentially of major concern to human health and the environment. Little is known about the spatial extent of contamination or how to manage these sites. Groundwater contamination has also been associated with dip sites.

It is estimated that there are 50 000 historical sheep dip sites in New Zealand, all with a history of pesticide contamination from chemicals such as arsenic, organochlorines (including dieldrin, lindane and DDT), organophosphates and synthetic pyrethroids. Sheep dipping has been required by law to control ectoparasites from 1908 to 1993.

A study of three historical sheep dip sites in the Waikato region determined the fate and extent of contamination. Dealing with contamination originating from sheep dip sites can be difficult as location may need to be accurately established. Detailed site histories, soil profiling and ground penetrating radar (GPR) were utilised to determine site location characteristics and associated subsurface features.

Soil samples (1-100cm) were analysed for contaminants in relation to spatial variation and migration down the soil profile. Preliminary screening results indicate that arsenic (8-1490 ppm), dieldrin (0-201 ppm) and lindane (0-16.5 ppm) were the main contaminants of concern.

Heavy metal contaminant fluxes were studied by deploying diffusive gradients in thin-films (DGT) into mesocosms to estimate resupply and remobilisation. Sequential extractions were utilised to determine heavy metal partitioning within soil profiles, findings will be discussed. The potential for phytoavailability, bioavailability and leaching were identified to enable more effective management and remediation