By Vaughn Hagerty
North Carolina’s health goal for GenX in drinking water would drop by one-fifth if state regulators choose to use preliminary data on the compound’s toxicity from the U.S. Environmental Protection Agency.
That newly published data, a reference dose representing a maximum level of daily oral exposure considered unlikely to affect a person’s health over a lifetime, resulted from an EPA assessment of GenX’s toxicity, a draft of which the agency released on Nov. 14.
The assessment also identified specific potential health hazards posed by GenX: Among other things, the liver may be especially susceptible and available data are “suggestive of cancer.”
EPA’s proposed reference dose for GenX is 0.00008 milligrams per kilogram of body weight for daily lifetime exposure. That equates to 80 parts per trillion (ppt), a conversion that simplifies comparisons to the concentration of GenX that North Carolina considers safe in drinking water.
Last year, the state Department of Health and Human Services (DHHS) derived its own reference dose of 100 ppt as one of a number of factors used to calculate North Carolina’s interim health goal of 140 ppt in drinking water.
In addition to the reference dose, DHHS also based its calculations on potential risks to a particularly vulnerable human population, infants, and assumed that drinking water would account for one-fifth of total exposure to GenX.
Plugging EPA’s draft reference dose into DHHS’ formula would reduce the health goal to 112 ppt.
Jamie DeWitt, a professor in the Department of Pharmacology and Toxicology at East Carolina University, said: “EPA’s proposal appears to align more closely with the state’s conclusions, though its methodology differed from the state in a number of ways.
“For example, unlike the state, EPA used statistical modeling techniques. It also used different factors to account for uncertainties such as differences between the ways a mouse and a human might be affected,” DeWitt said. “The EPA didn’t calculate a health advisory, so we can’t compare it directly to the 140 parts-per-trillion health advisory.”
For now, the state will stick with the current health goal, DHHS spokesman Cobey Culton said in an email response to NC Health News.
“The EPA report on GenX toxicity is in draft form and is subject to change after the public comment period. In the interim, we will continue to use our provisional health goal for drinking water of 140 parts per trillion that has been evaluated by the Secretaries’ Science Advisory Board. When the EPA releases its final reference dose, we will revisit our provisional health goal for GenX.”
The EPA will finalize the toxicity assessment following a 60-day window for public comments.
As with the state’s health goal, the reference dose is not an enforceable standard.
‘Less hazardous than PFOA’
GenX contamination surfaced as a public health issue in June 2017, following media reports that researchers had found GenX and similar substances in the Cape Fear River, downstream from the Chemours chemical plant on the Bladen-Cumberland county line near Fayetteville.
Because conventional municipal water treatment cannot filter fluorochemicals such as GenX, the compounds also wound up in drinking water provided by utilities serving more than 200,000 people in southeastern North Carolina.
Chemours officials said the GenX in the river was a byproduct of a manufacturing process that had been discharging wastewater into the Cape Fear since about 1980.
In November 2017, under pressure from the N.C. Department of Environmental Quality, Chemours stopped discharging its manufacturing-related wastewater.[sponsor]
Asked about the EPA’s draft toxicity report, a Chemours spokeswoman pointed out that the reference dose for GenX is larger than that for the substance it replaced, perfluorooctanoic acid (PFOA), also known as C8. A larger reference dose typically indicates less toxicity. EPA’s reference dose for GenX is four times that for PFOA, but both numbers are very small.
“While we are in the process of reviewing the draft EPA toxicity assessment for GenX, it is clear from the EPA report that GenX is significantly less hazardous than its predecessor compounds,” spokeswoman, Lisa Randall said.
Randall also said that Damian Shea, an N.C. State University professor serving as a Chemours consultant, indicated that using the EPA’s reference dose in a formula that assumes consumption by an adult rather than an infant would result in a health advisory of 560 ppt.
Shea, on behalf of Chemours, has criticized the state’s calculation of the GenX health goal, urging instead an approach yielding a far higher level: 70,000 ppt.
The Secretaries’ Science Advisory Board rejected that argument earlier this year, instead endorsing the 140 ppt number.
Variation in gauging health risks from chemical exposure is not uncommon, DeWitt said.
“Risk assessment is not an absolute science,” she said. “It is a process and depends on interpretation of the scientific evidence, which can vary depending on who is doing the interpretation.”
DeWitt compared the uncertainty to the uncertainty around hurricane predictions.
“Look at what happens when forecasters try to predict where a hurricane will fall,” she said. “We have lots of data to use to make the predictions, but they’re not 100 percent accurate. Risk assessments can be like this, too.”
Typically, scientists don’t test the effects of toxins directly on humans, she explained.
“Even if we did, humans are different, which is an uncertainty factor,” DeWitt said. “There’s uncertainty around the science due to the types of animals used, the endpoints assessed and other factors.
“Remember, scientific information changes regularly, and how we understand that information changes as our knowledge grows. For example, people used to regularly smoke during pregnancy, and now we accept that it is not at all healthy for a developing baby to get exposed to smoke.”
‘Data are suggestive of cancer’
The EPA’s risk assessment includes a summary of potential health hazards posed by exposure to GenX, based on available animal studies.
In particular, the EPA assessment highlighted the liver as vulnerable.
“Overall, the available oral toxicity studies show that the liver is sensitive to GenX chemicals,” according to an EPA fact sheet on the draft assessment.
“Animal studies have shown health effects in the kidney, blood, immune system, developing fetus and especially in the liver following oral exposure,” according to the fact sheet. “The data are suggestive of cancer.”
The 80 ppt reference dose in the draft report is for chronic or lifetime exposure. In addition, the report included a reference dose for subchronic exposure — more than a year but less than a lifetime — of 0.0002 milligrams per kilogram of body weight, or 200 ppt.
The EPA also released a draft risk assessment for perfluorobutane sulfonic acid (PFBS), another fluorochemical.
Unlike GenX, PFBS “doesn’t appear at high levels in N.C. drinking water intakes,” said Detlef Knappe, an N.C. State professor and one of the researchers who discovered GenX in the Cape Fear River and downstream utilities.