Collective Effects of Different Per- and Polyfluroalkyl Substances (PFAS) Chemicals on Migration Behaviors and Toxicity

Per- and polyfluoroalkyl substances (PFAS) are synthetic organofluorine chemicals that have been widely used in commercial products and industrial processes. Their ubiquitous occurrence, environmental persistence, and potential toxicity pose threats to the public and ecosystems. Due to the regulation on traditional long-chain PFAS, industrial applications of PFAS have shifted to novel short-chain PFAS. The simultaneous occurrence of traditional novel PFAS compounds leads to their co-transport in the subsurface and subsequent co-exposure to humans and wildlife. However, most previous studies applied unrealistic experimental conditions of single PFAS. Therefore, understanding may vary as to the real-world scenarios of co-occurrence. To better understand the migration of PFAS and their potential health risks, it is important to consider their collective effects during the investigation.

We investigated the collective effects of PFAS compounds with three proposed objectives, namely (1) summarizing PFAS co-occurrence, (2) investigating PFAS co-transport in the subsurface, and (3) studying toxicity due to PFAS co-exposure. Regarding the first objective, the occurrence of conventional long-chain PFAS and their novel alternatives in surface water and groundwater has been reviewed and summarized in this report. The review indicated a higher level of occurrence of PFAS in surface water than in groundwater. Our review also suggests that limited occurrences of novel PFAS substances have been identified to date. To address the second objective, the individual transport and co-transport of representative PFAS (i.e., PFOS and 6:2 Cl-PFESA) have been investigated via column experiments in silicon sand and subsequent breakthrough curve (BTC) simulations. Experimental observation indicated retardation of both conventional and novel PFAS compounds. More importantly, the transport of the PFAS alternative (i.e., 6:2 Cl-PFESA) is significantly enhanced by the PFAS co-occurrence. To address the third objective, the acute and chronic toxicity of PFAS co-exposure (i.e., PFOA and GenX) were investigated by in vivo experiments using zebrafish (Danio rerio). The observed toxicity in acute exposure is PFAS-dependent, with embryo death observed at different concentration ranges for PFOA, GenX, and co-exposure. Future studies with larger sample sizes are needed to confirm the trend. Moreover, we found that PFAS liver impacts increased with exposure levels, as evidenced by the concentration-dependent upregulation of selected genes.