April 6, 2021
Lack of "Forever Chemical" toxicity data worries toxicologists
As the saying goes, nothing lasts forever. However, some chemicals may persist in the environment effectively for eternity, causing potential health hazards and endangering habitats. Perfluoroalkyl and polyfluoroalkyl substances (PFASs)-common chemicals present in firefighting foam, dental floss, cosmetics, and rain jackets-are currently in the regulatory spotlight since they leak into water and soil but do not biodegrade due to their chemical durability.
Just like hydrocarbons, PFASs are mostly non-polar, hydrophobic molecules. This water-repelling quality makes PFAS useful as coatings for water, heat, and oil-resistant products.
PFASs contain many carbon-fluorine bonds; in many of these chemicals, fluorine appears everywhere that hydrogen could be. Fluorine is the most electronegative element, which means that its bond with carbon is extremely strong-the strongest of any carbon single bond. Once PFASs enter the environment or a human body, natural or biological conditions can do little to break these bonds.
Take a look at the ViridisChem toxicity profiles for the following PFASs: perfluorodecalin, tetrafluoroethylene, and perfluorooctanoic acid (PFOA). All three chemicals have a persistence score of at least 2.00; PFOA has the highest score of 4.00.
According to the Centers for Disease Control and Prevention, the acid was used to manufacture polytetrafluoroethylene but has not been in use since 2002. However, ViridisChem's toxicity profile indicates that any PFOA contamination from past manufacturing likely remains in the environment.
The profiles also highlight the health hazards of these three chemicals. They all have acute health scores above 2.50, with tetrafluoroethylene the highest at 3.63.
These data agree with the CDC's warnings of links between PFASs and liver damage, high LDL cholesterol, cardiovascular effects, thyroid disease, decreased antibody response to vaccines, and decreased fertility. Scientists found rats exposed to PFOA had higher risk for cancer and organ lesions in a National Toxicity Program study in May 2020.
Many toxicologists believe that more information regarding PFASs should be available to chemists, manufacturers, and policymakers. Environmental Working Group senior scientist David Andrews told Scientific American that more toxicity information for PFASs and other chemicals should be collected and distributed.
"Regulatory bodies have not kept up with the chemical industry, which has really moved away from PFOA and PFOS into hundreds of replacement compounds that are equally persistent and likely to contaminate a significant number of water systems across the country," Andrews said.
ViridisChem software could help predict the toxicity of PFAS replacements, whether they are built from existing molecules that have existing toxicity documentation or from novel chemicals with zero background information. The compounds, along with their structures and toxicity data, can then be stored in a chemical registration system such as CDD Vault for easy searching, comparison, and further screening.
The Danish EPA investigated many chemical alternatives to PFASs for textile coatings in a 2015 report. Below, the ViridisChem Chemical Analyzer software compares the toxicity profiles of two silicone-based options-hexamethyl disiloxane and dodecamethyl pentasiloxane-- that the report proposed with tetrafluoroethylene's profile. After determining the effectiveness of these chemicals as textile coatings, a comparison of their health hazards, toxicity, and persistence could help manufacturers practice green chemistry.
The EPA, U.S. Congress, and the Biden Administration are all aware of the dangers that PFASs pose.
In 2010, the EPA amended the Polymer Exemption Rule, which allows certain chemicals to bypass the typical review process for chemical manufacturing, to prevent PFASs from qualifying for exemption. Specifically, the amendment required "polymers containing as an integral part of their composition, except as impurities, certain perfluoroalkyl moieties consisting of a CF3- or longer chain length" to undergo a review process before manufacture.
In the House of Representatives, Rep. Madeleine Dean from Pennsylvania introduced the "Toxic PFAS Control Act" in 2019, aiming to ban all production and distribution of PFASs within three years. The bill has yet to move beyond committee deliberation.
At the federal level, President Biden's campaign pledged to "tackle PFAS pollution by designating PFAS as a hazardous substance, setting enforceable limits for PFAS in the Safe Drinking Water Act, prioritizing substitutes through procurement, and accelerating toxicity studies and research on PFAS."