Fifth national survey of pesticides in groundwater in New Zealand

Abstract

A total of 163 wells were sampled in New Zealand as part of the 2006 national survey of pesticides in groundwater. The aims of the survey were to update the national overview of pesticides in New Zealand's groundwater systems, to investigate temporal variation in pesticide concentrations between surveys, and to identify environmental factors associated with pesticide contamination of groundwater. Thirty‐one wells (19%) tested positive for pesticides, with 13 (8%) wells having two or more pesticides detected. Pesticides were measured in one or more wells in 11 out of the 14 regions sampled; they were not detected in wells from the Northland, Hawke's Bay, and Taranaki regions. Nineteen different pesticides and metabolites were detected in groundwater. Herbicides were the most common pesticide group detected (12), followed by insecticides (5) and fungicides (2). There was a total of 50 pesticide detections and, of these, 37 were herbicides and 25 were triazine herbicides. Levels of only two of the 50 pesticide detections exceeded 1 μg litre^‐1. Alachlor was detected in one well at a concentration of 34 μg litre^‐1 exceeding the maximum acceptable value (MAV) of 20 μg litre^‐1. All other pesticides were detected at concentrations less than 6% of the MAV. There were significant differences between shallow and deep wells with shallow wells being associated with pesticide detections. Higher dissolved oxygen and nitrate concentrations (indicating recent water), lower groundwater pH levels, urban and horticultural land use and unconfined aquifers were associated with pesticide detections. Comparisons of total pesticide concentrations in wells included in the previous surveys indicate that total target pesticide concentrations in groundwater are decreasing.

Keywords:

• alachlor
• triazines
• herbicides
• insecticides