A four yearly nationwide assessment of New Zealand’s groundwater resources has found very low concentrations of organic contaminants in close to two thirds of the wells tested.

ESR has been co-ordinating the groundwater survey since 1990 on behalf of 12 regional and unitary councils. The latest survey was conducted from September to December 2018.

As well as pesticides, the survey for the first time tested for glyphosate (the active ingredient in Roundup, a popular weed killer) as well as a suite of Emerging Organic Contaminants (EOCs) for all of the councils, with the exception of Hawke’s Bay, West Coast and Waikato Regional Councils, and Nelson City Council.

ESR principal scientist Murray Close says glyphosate was found in only 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 current 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.”

“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).

There is growing concern about EOCs and their potential impact on human and aquatic health, including groundwater.

Mr Close says EOCs are a class of compounds used for everything from the production and preservation of food to personal care products, as well as human and animal healthcare. 

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.

Find the full report here(external link).


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