Recently, we have addressed the evolving regulatory landscape for per- and poly-fluoroalkyl substances (PFAS), as the federal and state governments grapple with finding the best approach to handle PFAS releases from manufacturing facilities, fire and crash training areas, and industrial and municipal waste disposal sites into soil, groundwater, and drinking water systems. A growing awareness of PFAS persistence and the possible negative health effects at low levels in the environment also has resulted in an increasing number of lawsuits against manufacturers and distributors of PFAS and other potentially liable parties. This article discusses how scientific studies on PFAS toxicity and potential endangerment to human health and the environment have influenced such litigation.

How Dangerous are PFAS?

PFAS are a group of man-made chemical compounds that are now ubiquitous in the environment. They are absorbed readily following inhalation and ingestion, and are not metabolized in humans or laboratory animals.[1] Several federal agencies have investigated the toxicity of PFAS compounds, reviewing human epidemiological and animal laboratory studies, and reached differing conclusions.

In 2016, the United States Environmental Protection Agency (“U.S. EPA”) issued Lifetime Drinking Water Health Advisories for Perfluorooctanoic Acid (“PFOA”) and Perfluorooctane Sulfonate (“PFOS”)[2] in which the Agency determined that exposure to PFOA and PFOS, two of the most prevalent PFAS chemicals, may adversely affect fetuses during pregnancy and breastfed infants as well as the liver, immune system, and thyroid, and cause changes in cholesterol levels.[3] The U.S. EPA also concluded that there was “suggestive evidence of the carcinogenic potential” of PFOA[4] and PFOS[5] in humans. [6] As a result of its review of the scientific data, the U.S. EPA established a combined 70 parts per trillion (ppt) limit for PFOA and PFOS in drinking water systems, and recommended that providers take appropriate measures to protect their customers from ingesting higher PFAS concentrations.

In 2018, the United States Department of Human Health and Services (“HHS”) Agency for Toxic Substances and Disease Registry (“ATSDR”) conducted its own review of PFAS toxicity, which was reported in its Toxicological Profile for Perfluoroalkyls.[7] Based on its evaluation, ATSDR determined that associations existed between PFAS exposure and several negative health outcomes, including: pregnancy-induced hypertension/pre-eclampsia (from PFOA and PFOS); liver damage (from PFOA, PFOS and PFHxS[8]); increases in serum lipids, particularly total cholesterol and low-density lipoprotein cholesterol (from PFOA, PFOS, PFNA[9] and PFDeA[10]); increased risk of thyroid disease (from PFOA and PFOS); decreased antibody response to vaccines (from PFOA, PFOS, PFHxS and PFDeA); increased risk of asthma diagnosis (from PFOA); increased risk of decreased fertility (from PFOA and PFOS); and small decreases in birth weight (from PFOA and PFOS).[11] These results followed a 2016 evaluation of PFAS health impacts by the HHS National Toxicology Program, which found PFOA and PFOS altered immune function in humans.[12] Based on its assessment of the studies, the ATSDR published adult and child “intermediate” Minimal Risk Levels (MRLs) for PFAS compounds, as follows: 78 ppt and 21 ppt for PFOA, 52 ppt and 14 ppt for PFOS, 517 ppt and 140 ppt for PFHxS, and 78 ppt and 21 ppt for PFNA.[13]

The values developed by U.S. EPA and ATSDR represent the highest levels at which the respective agencies concluded that exposure to PFAS would not result in associated negative health outcomes. The U.S. EPA’s exposure limits reflect an assessment of health effects for the most sensitive populations (e.g. developing fetuses and newborns), designed to protect individuals over a lifetime of exposure to PFAS in drinking water. U.S. EPA’s Lifetime Health Advisory limits do not represent definitive cut-offs between safe and unsafe conditions. Rather, they reflect the Agency’s determination of an adequate margin of protection for individuals throughout their lives from possible adverse health effects. The ATSDR MRLs provide an estimate of the amount of PFAS a person can eat, drink, or breathe each day without an appreciable risk to non-cancer health effects. However, exposure above the published “intermediate” PFAS MRLs does not mean health problems will occur. Rather, the increased exposure acts as a signal for health assessors to further evaluate possible harms to human health from that specific exposure.[14] While U.S. EPA and ATSDR have recommended safe ingestion exposure levels, it is unclear what specific levels of PFAS found in blood serum mean in terms of possible health effects. Blood test results that show PFAS in blood serum do not inform the need for treatment of a health problem, nor do they predict or rule-out the potential development of future health problems.[15]

Additional studies have been influential in identifying PFAS health risks. In some of the most widely publicized PFAS epidemiological studies, the C8 Science Panel[16] announced in 2012 that human exposure to 50 ppt or more of PFOA in drinking water for one year or longer had “probable links” with certain human diseases, including kidney and testicular cancer, ulcerative colitis, thyroid disease, preeclampsia, and medically-diagnosed high cholesterol.[17] The C8 Science Panel’s studies evaluated health outcomes for nearly 80,000 community members exposed to PFOA contamination near a DuPont de Nemours, Inc. (“DuPont”) PFOA manufacturing plant in West Virginia. The panel of epidemiologists was created in connection with a 2005 settlement between DuPont and a group of plaintiffs who had alleged a variety of negative health impacts from drinking PFAS-contaminated water in order to assess whether or not a “probable link” between C8 exposure and human disease existed in the affected community. The panel’s “probable link” determinations relied both on their own findings and other studies.

The differences between the advisory exposure levels developed by U.S. EPA, ATSDR and other key authorities has drawn significant attention.[18] However, the basis for these differences are largely dependent on each risk assessor’s selection of critical effects[19] and uncertainty factors to derive reference doses,[20] as well as methodological principles regarding assumptions of exposure and relative source contribution, all of which underlie the calculations of ingested PFAS limits.[21] As the Michigan PFAS Science Advisory Panel stated: “there may be only limited scientific evidence for claiming one [advisory] or the other is ‘better.’…[Risk assessment] is an art of practice more than an exact science.”[22] As a result, the risk assessment results have varied depending upon the manner in which the associations between PFAS contamination and health outcomes are addressed, even as the scientific studies being relied upon have largely remained the same.

While the risk assessments conducted by U.S. EPA and ATSDR give significant weight to PFAS exposure and human health associations, the causal relationship between PFAS toxicity and adverse human health effects remains unclear.[23] Potential health effects are associated with PFAS exposure where epidemiological studies have found increases in those health effects and increased levels of PFAS in blood serum. However, these health effects may be caused by a variety of different factors, such as exposure to other environmental contaminants, making it difficult to assess whether PFAS exposure specifically is the cause of the observed health problems.[24] Although laboratory animal studies have helped to clarify whether a causal relationship exists by demonstrating health impacts in other animals, comparison of study results across species is difficult. Accordingly, the differences in elimination half-lives,[25] species differences in the mechanism of toxicity[26] and the lack of adequate mechanistic data,[27] and differences in measurement of exposure levels between epidemiological and experimental studies create difficulties in assessing how observed health effects in other species translate into potential health effects for humans.[28] Thus, while laboratory animal studies serve to supplement scientific understanding of associations demonstrated in epidemiological studies, causal relationships between PFAS exposure and human health outcomes are not yet well understood.

This lack of clarity has led some experts, like the 2018 Australian Expert Health Panel for PFAS, to conclude that there is no current evidence demonstrating a large impact on an individual’s health or overall cancer risk from PFAS exposure.[29] The Australian panel concluded that, while there are observed health effects associated with PFAS exposure, the level of health effect reported in people with the highest exposure is still within the normal ranges for the general population.[30] The panel also cautioned that the hundreds of epidemiological studies addressing the association between PFAS and health outcomes[31] are based on only a few populations and the observed effects may be explained by confounding variables, such as age, smoking, or socio-economic status.[32] Similarly, in issuing its health advisories, the U.S. EPA recognized the limitations of some epidemiological studies on PFAS exposure due to the failure to control for alternative risk factors.[33] Other studies of PFAS-impacted populations actually have rebutted the associations between cancer and PFAS exposure, finding no statistically significant increase in cancer rates in populations exposed to PFOA for multiple decades.[34]

Proving PFAS Claims

Due to the range and variability of study results, individuals who pursue PFAS litigation may find it difficult to establish a causal link between PFAS exposure and negative health impacts. In order to prevail, they generally must demonstrate that exposure to PFAS contamination has caused them harm. As discussed, while there are studies that support a positive association, nonetheless, it may prove difficult to tie incidence of PFAS exposure to a particular disease or illness. On the other hand, drinking water providers in PFAS litigation do not seem to face this potential evidentiary hurdle because they are not seeking relief stemming from a specific illness or disease allegedly caused by exposure to PFAS contamination. In the cases we have reviewed, the drinking water providers typically are seeking compensation to upgrade water treatment technologies to meet the 70 ppt PFAS limit recommended in U.S. EPA’s Drinking Water Health Advisories, and injunctive relief to require that defendants remediate PFAS-contaminated groundwater.

For example, in a case involving PFAS contamination that allegedly migrated from a 3M Company manufacturing facility in Alabama, both the West Morgan-East Lawrence Sewer and Water Authority (“WMEL”), and individuals who received their drinking water from the WMEL, brought suit to recover damages due to the alleged release of PFAS contaminants upriver from WMEL’s drinking water supply intake. The individual plaintiffs asserted that the drinking water to which they were exposed exceeded the U.S. EPA limits and ATSDR MRLs, thus causing them harm[35] by increasing their risk of cancer, immune-toxicity, thyroid disease, ulcerative colitis, and high cholesterol. These plaintiffs pinned their assertions of harmful PFAS levels on the U.S. EPA’s findings and those of the C8 Science Panel.[36] While the defendants admitted that PFAS concentrations measured in the WMEL water supply exceeded the U.S. EPA’s drinking water advisory limits and ATSDR MRLs, they disputed that an association existed between the PFAS in the drinking water supply and the asserted potential health outcomes.[37] The defendants also denied that the C8 Science Panel’s “probable link” determinations accurately summarized the results of epidemiological findings,[38] and further disputed that the PFAS levels found in the drinking water were harmful.[39] Moreover, in the absence of an existing federal or state regulatory framework, the defendants have asserted that their conduct was consistent with law, applicable standards of care, and industry practice.[40]

Litigation of the individuals’ claims is ongoing. In contrast, defendants 3M Company and Daikin America, Inc. settled with the WMEL for $35 and $4 million, respectively. Some commentators attribute the difference in outcomes to a less onerous evidentiary burden facing drinking water providers who need not demonstrate a causal link between exposure to PFAS contamination and human health outcomes.[41] Rather, the drinking water providers may rely on the EPA’s Health Advisories as evidence of a significant public health risk that must be addressed, without proving the actual occurrence of illness or disease from exposure to PFAS contamination found in the drinking water supply. For this reason, defendants in PFAS litigation appear more willing to settle with drinking water providers and municipalities than with individuals.[42] As a result, states and municipalities have initiated legal action seeking to hold manufacturers and users liable for costs to upgrade water treatment systems and to require clean-up of PFAS contamination.[43]

Yet even where states and municipalities have been able to point to exposure limits, conflicting scientific evidence has sometimes weakened cases against PFAS manufacturers.[44] In 2010, the Minnesota State Attorney General filed suit against 3M Company for $5 billion in alleged damages to natural resources from PFAS contamination.[45] However, a Minnesota State Department of Public Health report, released leading up to the trial, concluded that the cities affected by thirty years of exposure registered no increase in the rates of cancer or low birth-weight babies.[46] While the case had centered on alleged damages to the environment from PFAS contamination, the Minnesota Attorney General was expected to employ expert testimony on the health risks of PFAS exposure and thus bolster Minnesota’s case.[47] The release of the Minnesota State Department of Health report appeared to mitigate the threat of those claims,[48] as the parties settled within a week of the report’s release for less than one-fifth of the original amount sought.[49]

In an apparent attempt to circumvent this causation issue, a firefighter claiming to have been exposed to PFOA-laden aqueous film-forming foams (AFFFs) brought suit on behalf of all individuals residing in the U.S. with a detectable level of PFAS in their blood serum, seeking to hold PFAS manufacturers accountable to determine the chemical’s true health impacts. Hardwick et al. v. 3M Company, et al., 2:18-cv-01185 (S.D. Ohio 2018). In addition to monetary damages, the complaint requests the establishment of an independent panel of scientists—jointly selected by the parties and funded by defendants—to further study and evaluate the health effects of PFAS.

Although issues of causation remain in flux, litigation continues to ensue with complainants asserting claims for relief based on common law torts, including negligence (negligence per se and gross negligence), property torts (trespass), nuisance (public and private), intentional torts (battery), and product liability (defective product failure to warn and design defects). Notably, lawsuits arising from the widespread use of AFFFs-containing PFOA and PFOS-have grown so numerous that in November 2018, the United States Judicial Panel on Multidistrict Litigation granted an order to transfer and consolidate 75 cases from around the country. In RE: Aqueous Film-Forming Foams Products Liability Litigation, MDL No. 2873. Currently, the multidistrict litigation has grown to include more than one-hundred cases.[50]

While PFOA and PFOS have been phased out of manufacture and use in the United States, their unique physiochemical properties ensure that these chemicals will remain in the environment for the foreseeable future. Moreover, manufacturers have begun to replace PFOA and PFOS, in some cases with other PFAS compounds for which health-related data is lacking.[51] While there appears to be ample scientific evidence of an association between PFOA and PFOS and adverse health effects, the current scientific understanding of the causal mechanisms by which PFAS affects humans remains incomplete. Expert analysis of study results has led to assertions that state regulations imposing PFAS limits are overhyped and unnecessary,[52] while others contest that current advisories are woefully inadequate to protect human health and should be more stringent.[53] Nevertheless, many more lawsuits are likely to be filed as new PFAS-contaminated sites are identified monthly. It remains to be seen whether the results of further research studies will solidify the causal link between PFAS exposure and specific illnesses or diseases.