PFAS Molecules: A Major Concern for the Human Health and the Environment

Abstract

Per- and polyfluoroalkyl substances (PFAS) are a group of over 4700 heterogeneous compounds with amphipathic properties and exceptional stability to chemical and thermal degradation. The unique properties of PFAS compounds has been exploited for almost 60 years and has largely contributed to their wide applicability over a vast range of industrial, professional and non-professional uses. However, increasing evidence indicate that these compounds represent also a serious concern for both wildlife and human health as a result of their ubiquitous distribution, their extreme persistence and their bioaccumulative potential. In light of the adverse effects that have been already documented in biota and human populations or that might occur in absence of prompt interventions, the competent authorities in matter of health and environment protection, the industries as well as scientists are cooperating to identify the most appropriate regulatory measures, substitution plans and remediation technologies to mitigate PFAS impacts. In this review, starting from PFAS chemistry, uses and environmental fate, we summarize the current knowledge on PFAS occurrence in different environmental media and their effects on living organisms, with a particular emphasis on humans. Also, we describe present and provisional legislative measures in the European Union framework strategy to regulate PFAS manufacture, import and use as well as some of the most promising treatment technologies designed to remediate PFAS contamination in different environmental compartments.

Keywords: PFAS; PFOA; PFOS; ecosystem; human health; remediation technologies.

Figure 1

Overview of the general structure of non-polymeric, perfluorinated PFAS substances. Non-polymeric PFAS are compounds of variable composition and physicochemical properties that however share two common features. These are represented by the hydrophobic tail, composed by a variable number of carbon atoms at different degree of fluorination, and the hydrophilic head, which contains polar groups. The specific combination of these chemical determinants, namely the carbon chain length, the type of functional groups and the number of fluoride atoms, generates an enormous number of different PFAS molecules with ample downstream applicability. Some of the most common polar groups, are shown.

Figure 2

Examples of non-polymeric and polymeric PFAS substances. (A,B) PFOA and PFOS, two well-known non-polymeric PFAS are shown. Both these compounds possess a relatively long tail containing eight fluorinated carbon atoms, but differ in the chemical composition of the polar head group, which is a carboxylic acid for PFOA and a sulfonic acid for PFOS. Under specific pH environmental conditions, these functional groups can dissociate into the respective anion forms (i.e., carboxylate and sulfonate). (C) Exemplary structure of Polytetrafluoroethylene (PTFE), also known as Teflon, a polymeric PFAS belonging to the subgroup of fluoropolymers. This type of compound is constituted by a moiety of (CF2-CF2)_n atoms which is repeated up to thousands of times; (D) Exemplary structure of a lubrificant also known as Krytox, which is a polymeric PFAS belonging to the subgroup of perfluoropolyethers. In this case the (CF[CF3]−CF2−O)_n moiety is repeated between 10–60 times.

Figure 3

Schematic illustration of the PFAS environmental distribution and exposure routes for humans and biota. The environmental distribution of PFAS substances involves multiple dispersion routes and exposure pathways that link the sources to the final receptors, represented by humans and wildlife. Industrial manufacture processes, industrial uses and recycling activities, represent primary sources of PFAS emissions. Other indirect sources are the landfilling or the application of contaminated sludge to agriculture land. Volatilization, deposition, leaching and run off processes regulate the redistribution of PFAS between air, soil, water and sediment compartments. Collectively, these pathways contribute to the short-term and long-term exposure of aquatic ecosystems, terrestrial ecosystems and humans to PFAS substances, that can also enter into the food chain through bioaccumulation and indirect human exposure via the ingestion of contaminated food sources.