PFAS Cleanup Challenges and Solutions By James Peeples
Per- and polyfluoroalkyl substances (PFAS) are a class of about 5,000 human-made chemicals whose management and remediation present a challenging task for site owners and government agencies. PFAS have unique chemical and physical properties that have led to their wide- spread use in industrial and consumer products, ranging from aqueous film-forming foams (AFFF) used for fighting flammable liquid fires to spray-on products for fabrics that repel water and stains. PFAS, except in the polymerized form (e.g. Teflon), typically consist of two parts: (1) a hydrophobic and lipophobic carbon backbone where all the carbon atoms are bound to fluorine atoms (perfluoroalkyl) or there is a mix of hydrogen and fluorine atoms bound to the carbon backbone (polyfluoroalkyl), and (2) a hydrophilic functional group, which can be a carboxylic or sulfonic acid, as in the case of two widely used PFAS, perfluorooctanoic acid (PFOA) and perfluorooctanesul- fonic acid (PFOS). The carbon-fluorine bonds within the backbone of these molecules rank among the strongest bonds in organic chemistry and this strength together with the protective “shell” around the carbon backbone formed by the fluorine atoms impart an extreme chemical and physical stability to PFAS molecules (ITRC, 2020). If it were only for their extreme chemical and physical stability, PFAS would likely have found many uses in industrial and consumer prod- ucts; however, many of these “forever chemicals” also dissolve well in water, due to their hydrophilic functional group, and the carbon-fluorine backbone exhibits both hydrophobic and lipophobic properties allow- ing it to repel both water and oils. Collectively, these properties result in a substance that is slippery, noncorrosive, chemically stable and has a high melting point (ITRC, 2020); PFAS chemicals add oil and grease repellency and chemical/physical stability to products (ATSDR, 2020). These properties have resulted in widespread use of PFAS in indus- trial and commercial/retail products such as nonstick coatings (e.g., Teflon®), chemical- and temperature- resistant plastics and tubing, stain treatments for fabric (e.g., Scotchgard™, STAINMASTER®), photographic antireflective coatings, car wax, waterproof/breathable clothing (e.g., GORE-TEX), architectural composite resins, aerospace/ aviation products, mist-suppressant foams in electroplating, AFFF, and paper/cardboard coatings (e.g., popcorn bags and pizza boxes) and many other products/uses (ITRC, 2020). The key takeaway is that PFAS substances are incredibly useful and incredibly stable, leading to their widespread distribution and their long-term persistence in the environment (USEPA, 2020). These fac- tors have resulted in a challenging situation for both the regulated and regulatory communities. Virtually all people have been exposed to PFAS either directly, through products we use, or indirectly, through environmental exposure (ATS-
DR, 2020; USEPA, 2020). The Agency for Toxic Substances and Dis- ease Registry (ATSDR) reports PFAS are found in “the blood of people and animals all over the world and are present at low levels in a variety of food products and in the environment” (ATSDR, 2020). Toxicologi- cal and epidemiological studies have found links between exposure to some PFAS and significant health effects. Some studies in humans with PFAS exposures indicate the potential for PFAS to interfere with the body’s natural hormones, increase cholesterol levels, affect the immune system, and increase the risk of some cancers (ATSDR, 2020). While the PFAS family contains thousands of human-made compounds, only a few have received significant testing or study. Much more work is yet to be done to evaluate the health effects of a broader range of this very large and useful family of compounds. As the health and toxicological studies raise concerns over the poten- tial effects of PFAS on humans and other organisms, regulators have taken notice. PFAS compounds began to receive attention as emerging contaminants of concern in the early 2000s (ITRC, 2020). By 2002, PFOS, was voluntarily phased out of production in the United States (ITRC, 2020). Additional voluntary phaseouts of global production by eight PFOA manufacturers occurred in 2006 (ITRC, 2020). The United States Environmental Protection Agency (USEPA) announced a Lifetime Drinking Water Health Advisory of 70 parts per trillion (ppt or ng/L) of combined concentrations for PFOA and PFOS, two of the more commonly detected PFAS in 2016 (USEPA, 2016). Health advisories are unenforceable guidance providing information on con- taminants that can cause health effects and are known or anticipated to occur in drinking water (USEPA, 2016). In 2018, ATSDR set minimal risk levels in drinking water for four PFAS: PFOA at 78 ppt* (adult) and 21 ppt (child); PFOS at 52 ppt (adult) and 14 ppt (child); perfluorohexane sulfonic acid (PFHxS) at 517 ppt (adult) and 140 ppt (child); and perfluorononanoic acid (PFNA) at 78 ppt (adult) and 21 ppt (child) (ATSDR, 2018). In Feb- ruary 2019, USEPA released a PFAS Action Plan that listed targets and milestones but no hard deadlines. The Action Plan, among other items, includes the following: evaluating PFOA/PFOS for a maximum contaminant level (MCL) in drinking water and as possible hazardous
*ppt = parts per trillion
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csengineermag.com
may 2020
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