PFAS in Wilmington, NC

My notes on those early years

Shortly after moving to Wilmington, North Carolina in 2015 a ruckus over PFAS (per-and polyfluorinated substances) in the drinking water broke out. I set out to write about the NC science advisory process feeding into decision making about threshold levels of contamination but life happened and I dropped the project.

I was reminded of my notes on the project by the recent Executive Order to reform the Nuclear Regulatory Commission directing the NRC to reconsider its reliance on the linear no-threshold model for radiation exposure. The use of a linear no-threshold (LNT) model for PFAS exposure is a controversial issue. The entirety of the LNT model is argued to be outdated. The EPA’s 2024 final PFAS regulation uses no-threshold assumptions in its analysis.

These are my notes on those early years of public debate about GenX (one of many PFAS) in the drinking water in and around Wilmington, NC.

In the early 2000’s, the EPA began working with chemical company DuPont, a main PFAS producer, to reduce the drinking water concentration of two types of PFAS: perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). The chemicals are common in many, many contemporary goods and manufacturing processes.

A series of decree orders led to DuPont’s rapid reduction in production and sale of PFOA. This success was due to the ability to use a precursor of PFOA known as “GenX,” as a replacement chemical for PFOA.

A chemical plant run by DuPont Chemours (now just Chemours) is located along the Cape Fear River from which Wilmington, NC and other smaller towns source its drinking water. Since the 1980’s, Chemours produced PFOA and PFOS, and discharged GenX to the river as a byproduct waste.

In 2012, the NC Secretary’s Science Advisory Board (SAB) advised the Division of Water Resources to lower the allowable limit of PFOA to 1,000 ppt. This was half of the existing limit¹ but still higher than that considered acceptable by EPA consent orders at the time.

In 2017, the EPA published a public health advisory recommending that the combined concentration of PFOA and PFOS in drinking water not exceed 70 ppt.

Just a few days after this EPA update, North Carolina researchers published an average concentration of 631 ppt for the single chemical, GenX, in the Cape Fear River downstream from the Chemours plant. This was the study that kicked off huge controversy locally and nationally.

The lab director and author on the study advised drinking water managers that there is “not enough information to say that you shouldn't drink the water,” also expressed urgency to drinking water managers because GenX concentrations “exceed the current health advisory level for PFOA.”

Recalling the experience the researcher explained his motivations,

My goal was and is to drastically reduce the input of GenX and other chemicals into North Carolina water bodies and to keep them out of the drinking water... For Fortune 500 companies, the cost of proper wastewater treatment and air pollution control would not be a big burden.

In response to the sudden controversy, the North Carolina Dept. of Health and Human Services (DHHS) argued that according to their risk assessment the concentration of GenX falls well below a threshold value of 71,000 ppt and “pose[s] a low risk to human health.”

But, only a few weeks later, DHHS dramatically decreased their GenX threshold to 140 ppt citing EPA guidance to use different risk assessment methods.

A state professor and independent consultant for Chemours argued that the decision of a 140ppt threshold was the result of deep uncertainty

“Even though a chronic, gold-standard, lifetime-exposure study was available, they decided not to use it and substituted the 28-day sub-acute study, which is not what you do if you’re trying to look at lifetime exposure. That’s the main scientific error.

“They compounded the error by basically saying, ‘Since we’re using a study that’s not as appropriate as it should be, we’re going to use a 10-fold safety factor,’ when the appropriate study was available,” he said.

“The other scientific error was they used the body weight of a drinking water intake of an infant. Obviously, an infant is only an infant for a short period of time. For lifetime exposure you want to use a body weight and drinking water intake for an adult.”

The table below shows how advisory threshold levels changed in North Carolina from 2006- 2022. At no point was the water considered unsafe or dangerous to drink.

Changing threshold values for PFAS in drinking water, NC and federal.

The sudden change in the state’s GenX risk assessment left the public wary. State regulators responded to public concerns by explaining that,

This health assessment is not a boundary line between a “safe” and “dangerous” level of a chemical. Rather, it is a level that represents the concentration of GenX at which no adverse non-cancer health effects would be anticipated over an entire lifetime to the most sensitive population.

The statement reflects an EPA report from the early 1990’s describing the inherent subjectivities of defining public health thresholds for contaminates,

The existence of different [thresholds] need not imply that any of them is more "wrong"-or "right"-than the rest. It is more nearly a reflection of the honest difference in scientific judgment. However, on occasion, these differences in judgment of the scientific data, can be interpreted as differences in the management of the risk. As a result, scientists may be inappropriately impugned, and/or perfectly justifiable risk management decisions may be tainted by charges of “tampering with the science.” This unfortunate state of affairs arises, at least in part, from treating the [threshold] as an absolute measure of safety.

The Secretary’s Science Advisory Board (SAB), serving DHHS and DEQ, reviewed 140 ppt decision. SAB meeting minutes reveals the extent to which decisions about GenX thresholds were set against significant scientific uncertainty and differences in judgement,

• One panel member explained his concern about calculation assumptions when moving from studies of PFOA to GenX, “there’s a lot of uncertainty in this process that is not reflected in a single number… [The SAB member] did not hear anything that would cause him to choose that number over any other.”

• Another SAB member noted the extent of choice available in choosing values for calculating thresholds, variability ranged by orders of magnitude, and the choice of any particular value “is a policy matter, and is not based on science…rather than just picking numbers almost out of thin air” presenting a range of values may be a better approach for the SAB.

Nonetheless, the SAB’s final report justified the DHHS 140ppt decision including its use of infants as a basis for their calculations. SAB did this rather than point to the range of choice and trade-offs facing decision makers showing many thresholds to be defensible depending on priorities.

In the background of uncertainty about the safety of the drinking water were two relevant political and legal controversies.

First, in North Carolina, there was uncertainty about who- if anyone- could be held accountable for the existence of GenX in the water supply. As a byproduct chemical of the production process for PFOA, GenX discharge was unregulated under TSCA. As a result, the Dept. of Environmental Quality Secretary at the time, Michael Regan, argued that Chemours “is not breaking the law.”

Yet, North Carolina Governor Roy Cooper publicly considered the possibility of a criminal investigation into Chemours and a Wilmington scientist pointed to regulator notes from the permitting process to argue that Chemours was intentionally deceptive and “the discharges are illegal.”

Chemours expressed frustration that while DEQ demanded that it cease discharging GenX into the Cape Fear River, DHHS advised that current contamination levels did not warrant a public health warning. And anyway, said Chemours, the state “law allows various known human carcinogens in the drinking water at levels far greater.”

The second controversy concerned the scientific and advisory practices of the EPA.

In 2017, EPA Secretary Scott Pruitt announced that experts on the EPA’s 18-member science advisory board were no longer permitted to accept agency grants. Members were forced to choose between continuing to accept grant funding from the EPA or serve as a member of the panel.

For many environmental scientists, Pruitt’s new rule served only to place scientists representing industry interests on the advisory board presenting a conflict of interest. But for Pruitt, and those that would agree with him, it served to eliminate an apparent conflict of interest by having advisors receive agency grants for the problems they actively defined.

Concurrently, Pruitt worked to implement the then and now President Trump executive orders examining transparency of regulatory science. The effort specifically targeted the type of data and models required for risk assessment of environmental contaminant exposure including the use of the linear no threshold model².

The EPA proposed rule, announced in 2018, stated the attempt to “change agency culture and practices regarding data access so that the scientific justification for regulatory actions is truly available for validation and analysis” and took particular aim at the LNT,

In addition, this proposed regulation is designed to increase transparency of the assumptions underlying dose response models. As a case in point, there is growing empirical evidence of non-linearity in the concentration-response function for specific pollutants and health effects. The use of default models, without consideration of alternatives or model uncertainty, can obscure the scientific justification for EPA actions.

The 2024 EPA regulations setting threshold levels for PFAS at the lowest level in which they can be detected reportedly creates significant financial burdens on municipal water managers that exceed potential health benefits. There is also the lingering issue about the questionable appropriateness of the no-threshold model.

Finally, it is not clear (to me at least) that the available replacements for PFAS, to the extent they exist, are adequate and they potentially present no less problematic environmental and health impacts.

1. The Interim Maximum Allowable Concentration (IMAC)

2. Note that the person quoted as in support of Pruitt’s efforts is also the author of the paper in my prologue documenting the history of the LNT model and making a case for it being outdated.