A draft study of the risk posed by exposure to per- and polyfluoroalkyl substances, or PFAS, that was dubbed a "public relations nightmare" by the White House shows new safety levels for the chemicals seven to ten times lower than current thresholds.

The new toxicological profiles released June 20 by the federal Agency for Toxic Substances and Disease Registry (ATSDR), comparatively drop the level at which no harm would be expected from exposure to people into the single digit parts-per-trillion (ppt) range.

According to environmental chemists, the proposed ATSDR "minimum risk levels" or MRLs, translate roughly to 7-ppt for PFOS and 11-ppt for PFOA -- the two PFAS compounds which the state of Michigan has established cleanup standards for groundwater that people drink.

The U.S. Environmental Protection Agency health advisory level for PFOS and PFOA is a combined 70-ppt, a level some researchers call inadequate to protect public health.

The ATSDR proposes MRLs translating to about 70-ppt for PFHxS and 10.5 ppt for PFNA, two PFAS compounds for which there are no federal standards. The compound PFHxS is closely associated with AFFF, a chemical-laden firefighting foam.

The ATSDR uses MRLs as a screening tool to assess whether exposures at a given contaminated site represent a potential health hazard. They are not enforceable regulatory standards.

"This study confirms that the EPA's guidelines for PFAS levels in drinking water woefully underestimate risks to human health," said Olga Naidenko, a senior science advisor at the nonprofit Environmental Working Group.

"We urge EPA to collect and publish all water results showing PFAS contamination at any level, so Americans across the country can take immediate steps to protect themselves and their families."

The EWG estimates tap water supplies for 110 million Americans are contaminated with PFAS chemicals, according it its own analysis.

Public health and environmental groups, as well as legislators and regulators in numerous states including Michigan have demanded the ATSDR report's release ever since it was revealed the document was likely to push down safety thresholds for PFAS exposure.

Emails obtained in May by the Union of Concerned Scientists showed that ATSDR was preparing to release toxicological profiles severely ratcheting down PFAS safe exposure levels before the EPA and White House stepped in to blocked their release.

Lower safety levels could have significant impact on response and cleanup efforts at PFAS sites nationwide. Regulators have used the EPA level as a de-facto standard in the absence of enforceable rules on acceptable PFAS levels in drinking water, lakes and rivers.

The U.S. Defense Department will not supply long-term safe water to homes near current and former military bases contaminated by PFAS unless the well tests above 70-ppt.

Wolverine World Wide, which has polluted the Rockford and Belmont area groundwater with PFAS from tannery waste, has used 70-ppt as a cutoff threshold for supplying whole-house filtration systems to some houses with contaminated wells.

A 7-ppt MRL level for PFOS exposure is lower than Michigan's 12-ppt enforceable standard for that compound in surface water, a rule developed to account for bioaccumulation in fish.

Wolverine issued a statement Wednesday saying that it is "currently reviewing the ATSDR draft report and its preliminary recommendations."

U.S. Rep. Dan Kildee, D-Flint, issued a statement urging the Trump administration to address PFAS contamination with more urgency.

"The public has a right to have the most up-to-date information on toxic chemicals in their drinking water," Kildee said. "This federal study is deeply concerning because it demonstrates that PFAS chemicals are more dangerous to human health than the EPA has previously acknowledged. The Trump Administration must address PFAS contamination with more urgency. We must ensure that families and veterans exposed to these dangerous chemicals receive the health care and clean-up resources they need."

The study evaluates 14 PFAS compounds, but only developed MRLs for PFOS, PFOA, PFHxS and PFNA. Each of those are showing up at Michigan contamination sites.

It takes the health affects of humans exposed to PFAS into greater account that previous drafts from 2009 and 2015, which relied on studies of lab animals.

The draft study appears to rely heavily on research about health effects of PFAS exposure conducted by the C8 Science Panel, which evaluated the impact on 70,000 people in the mid-Ohio Valley area exposed to PFOA-tainted drinking water by DuPont.

Other human studies included those of people exposed to PFAS compounds at work, or general population studies of people exposed to "background" levels in the environment.

PFAS have been "extensively evaluated in humans and laboratory animals," the study notes, but says comparing toxicity across species is problematic because, among other things, humans take much longer to purge the chemicals from their bodies. The chemicals also cause different health problems in humans versus animals.

The scientific "endpoints" on which the ATSDR based its proposed MRLs are neurodevelopmental and skeletal effects in mice (PFOA), decreased weight in baby rats (PFOS), thyroid damage in rats (PFHxS) and decreased body weight and developmental delays in mice (PFNA).

"In the absence of evidence to the contrary, ATSDR assumes that humans are more sensitive to the effects of hazardous substance than animals and that certain persons may be particularly sensitive," the report notes. "Thus, the resulting MRL may be as much as 100-fold below levels that have been shown to be nontoxic in laboratory animals."

The reports notes that available epidemiological studies suggest associations between PFAS exposure and several ailments in people:

* Pregnancy-induced hypertension/pre-eclampsia (PFOA, PFOS)

* Liver damage (PFOA, PFOS, PFHxS)

* Increases in total and LDL cholesterol (PFOA, PFOS, PFNA, PFDeA)

* Increased risk of thyroid disease (PFOA, PFOS)

* Decreased antibody response to vaccines (PFOA, PFOS, PFHxS, PFDeA)

* Increased risk of asthma diagnosis (PFOA)

* Increased risk of decreased fertility (PFOA, PFOS)

* Small decreases in birth weight (PFOA, PFOS)

The report cites the International Agency for Research on Cancer's conclusion that PFOA is a possible carcinogen and notes that increases in testicular and kidney cancer have been observed in people exposed to high levels of PFOA and PFOS.

One of the experts who peer-reviewed the draft study is David Savitz, a Brown University epidemiology professor who chairs the Michigan PFAS science advisory board.

Carol Isaacs, head of the Michigan PFAS Action Response Team (MPART), which is coordinating PFAS testing at water and sewage plants across the state, said she was "pleased" to see the report released, but did not address specific questions about how it might affect the state's PFAS response efforts.

"Michigan looks forward to working with EPA and other state and federal agencies to carefully review the 852-page report and develop sensible and enforceable standards for PFAS that protect public health," Isaacs said in a statement.

The 30-day public comment period on the ATSDR report starts June 21. Click here for instructions on how to comment online or by mail.