National survey of pesticides in groundwater in New Zealand—2002

Abstract

A total of 133 wells throughout New Zealand were sampled for the 2002 National Survey of Pesticides in Groundwater. The survey objectives were to provide a national overview of pesticides in New Zealand's groundwater systems, to examine changes with time from earlier surveys, and to examine factors linked with pesticide contamination. The samples were screened for atrazine in the laboratory using an ELISA test kit and, as a result of this screening, samples positive for atrazine were analysed for 58 different pesticides using gas chroma‐tography‐mass spectrometry (GCMS). Blind duplicate samples (6%) and quality control samples (17% of the negative ELISA screen samples) were also analysed by GCMS. Three regional councils carried out their own pesticide surveys around the same time but submitted the samples for analysis to a different laboratory. Their results are included to give a national perspective. Pesticides were detected in 28 wells (21%), with 13 wells (10%) having two or more pesticides detected. There were one or more wells with pesticides detected in nine of the 15 regions. No pesticides were detected in wells from the Northland, Hawke's Bay, Manawatu‐Wanganui, Taranaki, Wellington, and West Coast regions. None of the wells in the 2002 survey had pesticides at levels above the maximum acceptable value (MAV) for drinking water (Ministry of Health 2000). Twenty‐one different pesticides were detected, including two triazine metabolites, usually at very low concentrations. Only three detections were at levels exceeding 1 mg m–3. Thirty‐nine out of the 58 pesticide detections (67%) belonged to the triazine group. As would be expected there were significant differences between wells with and without detected pesticides in factors associated with well or screen depth, and depth of water above the screen. In addition, lower groundwater temperatures and higher nitrate levels were associated with the increased detection of pesticides. A comparison with earlier surveys indicates that pesticide detections have been relatively stable over the past 12 years. After an adjustment to common reporting limits (reporting limits were substantially lower during later surveys), the overall frequency of pesticide detections were as follows: 1990 (7%), 1994 (13.6%), 1998 (11%), and 2002 (9%).