A baseline assessment of emerging organic contaminants in New Zealand groundwater.

Emerging organic contaminants (EOCs) are manufactured compounds, used for a range of purposes, that are a rising concern for freshwater quality, human and aquatic health. Their occurrence in groundwater has been demonstrated in several international surveys. We conducted the first baseline survey on EOC occurrence in New Zealand groundwater, using a wide-screening approach (723 compounds) and a novel stratified to mean residence time (MRT) randomised design to inform future monitoring. A total of 61 sites were sampled: 51 baseline sites from the State of the Environment (SOE) network in the Waikato region and 10 targeted sites located in the vicinity of known EOC sources for comparison. EOCs were detected at 91% of the baseline sites at concentrations ranging from 0.1 to 11,000 ng·L. Multiple groups of EOCs were encountered: pesticides (48 compounds), pharmaceuticals (11), industrial (10), preservatives/food additives (3) and personal care products (1). Similar diversity and concentration range of EOCs were observed at the targeted sites, with the addition of drugs of abuse and life-style compounds. EOC detections occurred across young (1-11 yrs. MRT), intermediate (11-50 yrs. MRT) and old (50-250 yrs. MRT) groundwaters with higher concentrations and more types of EOCs detected at sites in the youngest age category. Concentrations of the 73 compounds detected at baseline sites were comparable to those found in overseas groundwaters with 28 compounds measured at concentrations greater than the EU maximum admissible concentration for pesticides. We used the survey results to: review current pesticide monitoring; propose complementary monitoring; identify potential EOC groundwater tracers and identify compounds for which cost-effective national laboratory capability is needed. The Waikato survey results demonstrated ubiquitous occurrence of unmonitored, unregulated EOCs in groundwater and limitations in using targeted approaches to establish monitoring.