Traces of organic contaminants – among them chemicals used to make plastics and sunscreens – have been found in two-thirds of New Zealand's wells.

But ESR scientists say these were detected at very low concentrations in the latest survey of the country's groundwater.

The survey, covering 135 wells on behalf of 12 regional authorities, was carried out between September and December last year.

ESR tested for a range of compounds called emerging organic contaminants (EOCs), using a technique that measured their concentration at parts per trillion of water.

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It came amid growing concern about EOCs and their potential impact on human and aquatic health, including groundwater.

ESR principal scientist Murray Close said the compounds were 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."

The most commonly found EOC was bisphenol-A (BPA) – an industrial chemical used to make certain plastics and resins – while there were also frequent detections of OMC and BP3, both used in sunscreens, and artificial sweetener sucralose.

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

Close said there were no known health or environmental risks – but at the same time there were generally no health guidelines associated with EOCs.

"The contaminants are widely used and do make their way into the environment in low concentrations."

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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.

For the first time, the survey also tested for glyphosate, the controversial active ingredient in popular weed killer RoundUp.

It was found in only one well from the wells tested – and the level detected was well below – or more than 400 times lower - the World Health Organisation-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," Close said.

"None of the sampled wells exceeded safe drinking water standards, with most pesticides detected at less than 0.5 per cent of the maximum acceptable value."