From 1849 through to 1993 it was a legal requirement in New Zealand to treat sheep with insecticides to control external parasites ie: keds, ticks and lice. As a result, it has been estimated there are 50,000 former sheep dip sites scattered throughout New Zealand. In Marlborough, it has been estimated there are at least 100 on the Wairau plains alone. There are also a limited number of former cattle dip sites and footbaths that were used to prevent footrot.
A range of different chemicals has been used in sheep dips and footbaths. Many of these, especially those used up to 1980, are considered environmentally persistent and toxic eg: arsenic and organochlorine pesticides ie: DDT, Dieldrin and Lindane. Their use and disposal has created a legacy of soil and water contamination at some sites, with concentrations of chemicals that are often hazardous to humans, livestock and the environment. For example at some former sheep dip sites in Marlborough, concentrations of arsenic (up to 8810 mg kg-1) and/or organochlorine pesticides (up to 19 mg kg-1) hundreds of times the soil guidelines for grazing stock have been measured.
Managing Former Sheep Dip Sites
The present day risk a former sheep dip site presents ranges from low, to significant where stock health is affected, drinking water supply is impacted, or food is contaminated. The more that is known and understood about a former sheep dip site the better it can be managed to limit the risk it presents to humans, livestock and the environment.
To assist land owners and farmers to safely manage former sheep dip sites and any associated contaminated soils, four factsheets have been produced. The general premise is that land owners or farmers should identify former sheep dip sites and exclude stock from around the dip site and any surrounding contaminated land as a precaution. The factsheets also detail other actions to protect the health of stock (sheep, cattle, pigs and poultry), water supplies, edible crops, wild food, and children and visitors to the farm.