Outcomes of the first combined national survey of pesticides and emerging organic contaminants (EOCs) in groundwater in New Zealand 2018

Highlights: • First national groundwater survey of emerging organic contaminants for New Zealand • EOCs found in 70% of samples at low levels • Glyphosate only detected in one of 135 wells • 68 wells (24.4%) out of 279 wells with pesticides detected The first national survey of Emerging Organic Contaminants (EOCs) involved sampling 121 wells located throughout New Zealand and analysis for a suite of 29 EOCs. This survey was carried out in conjunction with the 2018 national survey of pesticides in groundwater, a survey that is conducted on a four-yearly basis which included the analysis of glyphosate for first time. A total of 227 EOCs were detected in the 85 wells (70%). There were 29 different EOCs in the analytical suite and 25 different EOCs were detected in at least one well. The highest concentration measured was 655 ng/L for sucralose, an artificial sweetener. These results indicate that EOCs, sourced from either animal or human effluents/activities, are making their way into shallow groundwater systems and can be detected at low concentrations. A total of 135 wells were analysed for glyphosate, glufosinate and their principal metabolites. There was only one detection of glyphosate at a concentration of 2.1 μg/L. This well showed evidence of poor wellhead protection and the contamination likely came from containers that were stored near the well. A total of 279 wells were sampled and analysed for pesticides and 68 wells (24.4%) contained detectable residues of pesticides, with 28 of these wells having two or more pesticides detected. The maximum number of pesticides detected in one well was six. None of the sampled wells exceeded the Maximum Acceptable Value (MAV) for drinking water in New Zealand and the concentrations of most of the detected pesticides were equivalent to less than 0.5% of the MAV. Comparisons with earlier National Surveys of pesticides in groundwater in New Zealand indicate the frequencies of pesticide detections have remained similar over the last 16 years, with higher detection frequencies occurring before that time.