Ohakea residents affected by chemical contamination from the Air Force base need more and better testing and more open information from the Defence Force, lawyer Tim Gunn says.

But a Defence Force spokesperson says it has been completely open and is using the right test for this stage.

Gunn works for Shine Lawyers in Auckland, which deals in civil and insurance litigation. The law firm's Australian parent company is working on a class action lawsuit against the Australian Defence Force concerning exposure to chemicals in Oakey, Queensland.

In December the New Zealand Defence Force (NZDF) told councils and residents that PFAS chemicals used in firefighting foams were present in groundwater around its Ohakea air base. Gunn said NZDF knew about the contamination as early as mid-2015.

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"This is a dangerous case of the perpetrators also being the gatekeepers to vital information that holds life-altering weight to the community."

The NZDF told Horizons Regional Council about possible contamination in October 2015, the spokesperson said, and it carried on investigating "carefully and methodically" after that.

New Zealand didn't have a drinking water guideline for PFAS until 2017, and the NZDF discovered PFAS had moved outside the Air Force base only in September last year.

It has since commissioned two rounds of testing, by AsureQuality.

The latest results increased the number of Ohakea households that have drunk bore water with unacceptably high levels of the chemical from five to eight.

Gunn has seen people harvesting watercress from ponds near the base. He said residents should ask for tests of surface water, soil, plants and their own blood as well as the groundwater tests.

Residents have been advised not to eat a lot of food from their land, as a precaution, because small amounts of the chemical can accumulate in their bodies.

Gunn also said New Zealand tests for PFAS compounds are not as effective as the TOP Assay test used in Australia. But the NZDF spokesperson said current tests were to assess the risk to households and the TOP Assay test would be used if long-term remediation was done.

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The PFAS scare is older in Australia, with New Zealand about three years behind. The chemicals are toxic, soluble and very long lasting.

Small amounts build up in the body and Queensland's Department of Environment and Science says they can cause health problems including liver damage, benign tumours and thyroid disease.

In Australia test results were put up online, with a map of the area affected, Gunn said.

In New Zealand the Ministry for the Environment is the lead agency dealing with PFAS contamination near several NZDF sites. Its website has published NZDF test results, and results from the latest round of testing near Ohakea.

The website says there are no acute health risks for people or stock from ingesting small amounts of the chemical, and it's okay to sell stock, milk and food grown on the land commercially.

Mr Gunn believes the contamination will eventually affect land values near NZDF sites. He's looking for owners interested in being part of a class action, but said better information about the extent of the problem is needed first.

Horizons Regional Council is investigating the contamination, and may prosecute the NZDF.