The Environmental Protection Authority says it has begun a formal investigation into whether firefighting foams with banned chemicals in them are being used or stored in New Zealand.

Photo: 123RF

The foam has contaminated groundwater underneath the air force bases at Ohakea and Woodbourne with the chemicals PFOS or PFOA, which triggered global health alerts back in 2000.

"Given there is significant public interest in this issue, and information is already in the public domain, the EPA considers it appropriate to let people know we are investigating," the EPA said in a statement.

The focus was airports and "other locations".

Blenheim's water supply tested clear at the weekend.

The EPA said the use of these foams has not been legal since 2006.

However, Auckland Airport last week told RNZ it was still using a PFOA foam. But as late as yesterday officials still expressed uncertainty about that, and this afternoon the EPA told RNZ it "can't comment" about Auckland airport.

Wellington Airport also confirmed the foam was still being used. It said there are no ground drinking water sources which would pose a health risk in its vicinity.

Tiny traces of the chemical were found in milk from dairy farms near the Ohakea base. However the Ministry for Primary Industries said the levels were so low the laboratory would not normally report them, and they pose no food safety risk.

Several states in the US have recently brought in enforceable limits on these chemicals in drinking water up to 100 times lower than New Zealand's health advisory level.

A 2002 OECD hazard assessment on the chemicals concluded that PFOS and its salts were "persistent, bioaccumulative and toxic to mammalian species", and similar concerns applied to PFOA.

Health and environmental concerns about the foams have been mounting globally for 17 years but New Zealand has had health guidelines on them only since April.

Those guidelines were only brought in because they were joint guidelines with Australia, which was forced to act by a growing scandal over use of the foams there. It has begun a huge inquiry, covering 20 airports and 18 defence sites so far.

It remains inconclusive if the foams cause cancer, although the UN's persisent organic pollutants review committee in 2016 agreed PFOS and PFOA were linked to six diseases, including some cancers, and warranted a "global response".

New Zealand's new PFOS guideline - at 70 parts per trillion - is the same as the EPA's guidleine in the US, but New Zealand's PFOA level - at 560 parts per trillion - is eight times higher.

The Defence Force said it had not used foams containing the chemicals since 2002, while the Fire Service has not used them since 2007. However, they persist indefinitely in nature and for several years in the body.

The EPA said the priority was to identify the types of foams held, whether they had been used or not, and how they were stored.

"If any do not have an appropriate approval, the EPA will check that they are safely stored."