Groundwater pesticide survey of interest to water suppliers

A total of 165 wells were sampled as part of the 2014 national survey of pesticides in groundwater, a survey that is conducted on a four-yearly basis. The survey aims were to update the national overview of pesticides in New Zealand’s groundwater systems, to investigate temporal variation in pesticide concentrations, and to identify environmental factors associated with pesticide contamination. Samples were analysed for around 80 pesticides using gas chromatography with mass spectrometry detection. Pesticides were detected in 28 wells (17%), with two or more pesticides detected in 10 wells (6%). Pesticides were detected in wells from six of the 13 regions sampled.

One well contained a pesticide (dieldrin) at a concentration greater than the maximum acceptable value (MAV) for drinking water. Twenty-one different pesticides were detected, with most concentrations being less than 0.1 mg m-3. Only four of the 51 pesticide detections exceeded a concentration of 1 mg m-3. Comparisons with earlier surveys indicate similar levels of pesticide detections in groundwater over the last 12 years, with higher levels of detections before that time. The majority of wells sampled in each national survey have not had pesticides detected; where detected, the concentrations were mostly less than 0.1 mg m-3 and, with the exception of dieldrin and terbuthylazine, less than 5% of MAVs.

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