Survey of pesticides in New Zealand groundwaters, 1994

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Abstract
A survey of pesticides in groundwater throughout New Zealand was conducted in 1994 by the Institute of Environmental Science and Research for various Regional and District Councils. Wells were selected on the basis of the importance of each aquifer to the region, the proximity of particular land uses, and the extent of application of pesticides in the area—recognising that shallower, unconfined aquifers would be more at risk than deeper aquifers. Throughout New Zealand, 79 wells were sampled plus 39 wells sampled during a more intensive survey in Marlborough. There were no wells with pesticides detected above the Maximum Acceptable Value (MAV) for drinking water, indicating that all the water tested was suitable for drinking. Pesticides were detected in 13 out of the total of 79 wells (16.5%) excluding the Marlborough survey. If this survey is included, then 16 out of a total of 118 wells (13.6%) showed detectable pesticides. Most (78%) pesticide concentrations were below 1 mg m−3 with 52% below 0.25 mg m−3. In total 10 different pesticides were detected, with the triazine group occurring most often. Contaminated wells were significantly shallower, had higher water tables, had less depth between the water table and the well screen, and had slightly lower temperatures than uncontaminated wells.

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