More than 600 Katherine residents have had their blood tested for PFAS.
The free and voluntary testing program ends on April 30.
The town-wide response is believed to one of the biggest ever in Australia to community blood screening for PFAS.
Launched in March last year, the program tested the blood of people who live and work, or who have previously lived and worked, in the RAAF Base Tindal investigation area.
The Federal Health Department is not providing results to the tests citing privacy considerations.
A department spokesman said the large number of residents who had been tested already was a "positive uptake" of the program.
The numbers of residents tested at Williamtown is believed to be about 200 with about 75 in Oakey.
Local GP P.J. Spafford, who is still doing the testing at Gorge Health, went public last year after being alarmed by the early results.
After the first 100 tests, Dr Spafford said he was concerned, not only with high PFAS levels being found in Katherine, but a particular chemical called PFHxS, part of the PFAS family of chemicals used in firefighting foams at the Tindal RAAF Base which have long leached into the Katherine water supply.
He asked for federal guidance on how to discuss the high PFHxS readings with patients.
Dr Spafford said: “Reading other studies, the levels we are getting here are way above those seen in America and Europe and the toxicity of PFHxS much greater than the other PFAS chemicals.”
PFHxS has “long-range transport potential” and higher bioaccumulation in humans than PFOS.
It lasts longer in your body, some estimates are about 10 years.
European agencies have rated PFHxS “as a substance of very high concern” based on animal and human data that showed the chemical might have more potential to bioaccumulate in humans than PFOS.
Australia’s chief medical officer, Professor Brendan Murphy, last year said a positive blood test for PFAS contaminants would not indicate, by itself, any harm to a person’s health.
“Blood levels are not predictive of health problems in individuals. There is no consistent evidence of PFAS resulting in specific health impacts therefore levels considered higher than the Australian general population may have no impact on the individual,” the federal Health Department said.
There is no practical treatment available to lower levels of PFAS in people, the department advises.
The Australian National University has been contracted by the Federal Government to prepare an epidemiological study for Katherine which is expected to draw from those blood test results.
The study is expected to take several years yet.
The ANU says it will compile "a blood serum study to define the serum PFAS concentrations (mean and range) of participating residents of Williamtown, Oakey and Katherine, and to compare blood PFAS levels to those of people residing in non-contaminated areas in similar townships in Australia".
In its preamble to the study, the ANU says:
"Studies have found evidence that higher levels of PFOS or PFOA in a person’s blood can lead to higher blood cholesterol levels; there is also evidence that exposure to PFAS may lead to a decreased response to some vaccines, may be associated with reduced kidney function, and may be associated with some cancers, particularly testicular and renal cancer".
But an independent expert health panel established by the Federal Government last year says there is mostly limited, or in some cases no evidence, that human exposure to PFAS is linked with human disease.
The panel concluded there is “no current evidence that suggests an increase in overall cancer risk”.
Katherine's blood tests are collected through Gorge Health on Saturdays between 8-10am.
Walk in, no appointment, PFAS testing and discussing results only or phone the clinic on 8963 6200 to make alternative arrangements.
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