On April 8, 2021, the U.S. Environmental Protection Agency (EPA) released an updated toxicity assessment for perfluorobutane sulfuric acid (PFBS). This assessment comes as part of the EPA’s larger PFAS Action Plan, aimed to increase the amount of research and publicly available information on chemicals in the PFAS family.
PFBS, which is part of the larger group of PFAS compounds, is a replacement chemical for perfluorooctane sulfonate (PFOS), which is no longer used in United States manufacturing. PFBS is mainly used as surfactants and repellants to make water- and stain-resistant coatings, and is commonly found in consumer products such as carpeting, carpet cleaners, and floor wax. PFBS has a half-life of a little over one month, compared to 3.8 and 5.4 years for perfluorooctanoic acid (PFOA) and PFOS. Humans can be exposed to PFBS through contaminated drinking water, polluted air, and contact with PFAS containing products. However, the EPA’s toxicity assessment focuses only on the potential human health effects associated with oral exposure. In animal studies, oral exposure to PFBS has demonstrated potential effects on thyroid, reproductive organs, developing fetus, and kidneys. Notably, the EPA’s data is inadequate to evaluate cancer risk at this time.
As a result of its assessment, the EPA has published chronic and subchronic oral reference doses, or RfDs (i.e., “safe doses”) for PFBS. By way of background, the chronic reference dose represents the estimated amount of a chemical that a person can ingest daily over a lifetime that is unlikely to lead to adverse health effects. The subchronic oral reference dose represents the estimated amount of a chemical that a person can ingest for less than a lifetime time (generally less than 10 percent of a human lifespan) that is unlikely to lead to adverse health effects.
The updated assessment concludes a subchronic RfD of .001 mg/kg-day (milligram per kilogram of body weight per day) and a chronic RfD of .0003 mg/kg-day, whereas the initial assessment set a range for safe long-terms exposure of .001 mg/kg-day to .0003 mg/kg-day. That initial assessment broke from EPA precedent of setting a single value for safe daily doses, and the updated assessment brings the values back in conformity with other toxicity assessments performed by the EPA. For purposes of comparison, the toxicity assessment suggests that PFBS is less toxic than PFOA and PFOS, which have chronic RfDs of .00002 mg/kg-day.
Like other PFAS compounds, PFBS remains unregulated at the federal level. However, the EPA has advised that the toxicity assessment is available to provide state and local governments with the tools needed to better understand PFBS and help inform local actions to protect public health.