Pesticides in groundwater

ESR carries out a national assessment of pesticides in groundwater every four years.

The four-yearly survey is for district and regional councils, to assess the quality of their groundwater resources. Samples are taken from approximately 165 wells and tested for a range of over 80 pesticides. ESR has been co-ordinating this groundwater survey since 1990.

The most recent survey in 2018 tested for glyphosate for the first time, along with a number of Emerging Organic Contaminants (EOCs). Glyphosate is the active ingredient in a popular weed killer.

Glyphosate was only found in one well from the 135 wells tested – and the level detected was well below (over 400 times lower) WHO recommended health-based value.

“The majority of the wells in the survey showed no change in the amount of pesticides present compared to previous surveys, with less than a quarter of the wells having low levels of pesticides detected,” said ESR principle scientist Murray Close.

“None of the sampled wells exceeded safe drinking water standards, with most pesticides detected at less than 0.5% of the maximum acceptable value (MAV).”

Wells were also tested for the first time for a range of emerging organic contaminants (EOCs) using a highly sensitive analytical technique that measures EOCs at extremely low concentrations (parts per trillion). The survey tested for close to 30 of these compounds including a diverse range of products such as caffeine and artificial sweeteners along with pharmaceuticals such as pain relief products, contraceptive pills and sunscreen.

“We found these compounds in 70 per cent of wells and detected 25 of the 29 compounds we tested for.”

Overseas research links the discovery of EOCs in groundwater to wastewater sources, including municipal treatment plants, septic tanks, farming activities, as well as indirectly from surface water.

Mr Close says there are no known health or environmental risks, however there are generally no health guidelines associated with EOCs. "The contaminants are widely used and do make their way into the environment in low concentrations.”

The survey recommends that monitoring of groundwater resources is extended and that research is carried out to investigate the likely risks for the EOCs detected in this study including any impacts on ecological systems.

ESR also undertake more general, ‘on-request’ assessments of regional groundwater quality for councils.