ASSESSMENT OF PESTICIDE CONTAMINATION OF GROUNDWATER IN NEW-ZEALAND .2. RESULTS OF GROUNDWATER SAMPLING

Seventeen areas throughout New Zealand were ranked according to an ind ex of potential pollution, and a selection of wells in six of the high er-ranked areas were sampled and analysed for a range of pesticides. L and use in these areas includes market gardening, cropping, pipfruit, and kiwifruit orchards. The groundwater systems include shallow alluvi al gravel, sand, basalt, and pumice aquifers. A total of 82 wells were sampled. Six wells had detectable levels of pesticides and an additio nal three wells had trace concentrations of an unidentified pesticide. Seven different pesticides were detected, mostly at concentrations < 1 mg m-3. One well had 37 mg m-3 atrazine and another had 1.7 mg m-3 p rocymidone. These pesticides were detected in the same wells on subseq uent sampling occasions at lower concentrations. The level of 37 mg m- 3 exceeded the health advisory limit for drinking water (3 mg m-3) of atrazine which has been established by the United States Environmental Protection Agency. The regions sampled in this survey were expected t o have the greatest potential for pesticide contamination because of a combination of high pesticide use and vulnerable groundwaters; theref ore the level of contamination in groundwater elsewhere in New Zealand should be lower than the levels found in this survey. Although the le vels of pesticides were generally very low, unconfined groundwater in New Zealand can be contaminated by pesticides and in some situations t here can be significant contamination.