The United States Environmental Protection Authority has significantly lowered its recommended safe level for the chemicals perfluorooctane sulfonate and perfluorooctanoic acid in drinking water, throwing investigations around the Williamtown RAAF base into disarray.

Until now, authorities in NSW have been basing testing of bore and tank water in the red zone around short term exposure limits set by the US EPA in 2009.

A safe level of PFOS was considered to be anything below .2 micrograms per litre and for PFOA, below .4 micrograms per litre.

However on Thursday long-awaited “lifetime” advisory levels were released by the US EPA, finding people should not drink water that has a combined concentration of pfos or pfoa above .07 micrograms per litre.

The decision means some people in the Williamtown contamination area whose water was previously considered safe for consumption may now be over the American threshold.

A report accompanying the new US levels found the “weight of evidence” for human studies supported the conclusion that exposure to the chemicals was a human health hazard.

It also found while the dominant source of human exposure to the chemicals was diet, indoor dust was an “important source”, especially for children.

“For highly exposed children … PFOS exposure from dust was estimated to be approximately two times that from food,” it said.

Greens Senator Lee Rhiannon said the report “leaves no doubt about the need for immediate response from state and federal governments to the health crisis facing local residents and affected airport workers”.

“This must serve as a massive wake up call for state and federal health authorities and the airport and defence agencies responsible for these contaminated sites to address the health of local residents and airport workers,” she said.

“Regular blood testing must be immediately provided along with safe drinking water. Ways to remove the contaminated water and soil needs to be a government priority.

“State and federal authorities should make this US EPA report available to the public and provide a responsible plan to deal with the serious implications.”