Unique Approach to Measure Per- and Polyfluoroalkyl Substances Uptake in Fish, Mussels, and Passive Samplers

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Widespread occurrence of per- and polyfluoroalkyl substances (PFAS) mixtures has been reported in groundwater, surface water, drinking water, and wastewater nationwide. There is concern about uptake by wildlife and how long PFAS remain in tissues upon exposure, which has ramifications for pathways to humans through fish consumption. Despite the extensive and rapidly growing literature on PFAS occurrence, fate, and effects, there are few controlled studies (laboratory or field) focused on uptake and bioconcentration factors (BCF) for PFAS in freshwater fish and mussels.

To address these gaps, scientists from the U.S. Geological Survey (USGS), Harvard University, the University of Rhode Island, and the University of Colorado Denver collaborated to advance understanding of PFAS uptake and bioconcentration by aquatic organisms.

The research was done at a legacy fire-training area contaminated by PFAS - derived from aqueous film-forming foam (AFFF)s - on Cape Cod, Massachusetts. This location was selected based on previous and ongoing research documenting the fate and transport of PFAS in groundwater at the site that contains a complex mixture of precursor and acid compounds at high concentrations, thus providing an ideal natural field laboratory for conducting exposure experiments to evaluate uptake of PFAS under dynamic ambient conditions.

Scientists used on-site mobile laboratories to conduct this controlled field-based exposure experiment. Freshwater fish (the fathead minnow, Pimephales promelas) and mussels (the pond mussel, Ligumia subrostrata) were exposed to the AFFF-contaminated groundwater, and groundwater from a reference site that was representative of low-level regional background concentrations in the sole-source aquifer that serves as the primary drinking water supply on Cape Cod. PFAS concentrations in water and bioconcentration into fish and mussels were measured periodically during a 21-day exposure period. PFAS also were measured in passive samplers (polar organic chemical integrative samplers [POCIS] and polyethylene tube samplers [PETS]).

This unique field experiment provided an understanding of PFAS uptake and bioconcentration by fish and mussels from a complex mixture under dynamic and environmentally relevant concentrations. PFAS concentrations observed in this study were consistent with previously reported concentrations for reference and contaminated groundwater at the site. The reference groundwater had 9 of the 25 PFAS measured at total concentrations ranging from 120 to 140 nanograms per liter. In contrast, the AFFF-contaminated groundwater had 17 of the 25 PFAS measured, with total concentrations as much as 850 times greater than those in the reference groundwater samples.

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PFAS BCF varied by species, sex, groundwater type (reference compared to contaminated), and specific compound, and generally increased with increasing fluorocarbon chain length and were greater for sulfonates than carboxylates. PFAS BCF were greater for fish than mussels (maximum fish=1,000 liter per nanogram; maximum mussel=200 liter per nanogram). Uptake for most PFAS in male fathead minnows increased at a consistent rate over time in contrast to female fish that in general had an initial increase in tissue concentrations followed by a decrease during the exposure timeframe. PFAS were concentrated more in POCIS compared to PETS and both increased at a consistent rate over time. PFAS uptake by passive samplers mostly mimicked uptake by fish but not by mussels.

This mobile laboratory approach is an important step in extrapolating results from highly controlled laboratory experiments to highly variable natural systems because it incorporates realistic and dynamic environmental PFAS concentrations with control over other environmental factors. The variable uptake and bioconcentration of differing PFAS by fish and mussels provide an understanding of the PFAS that other wildlife and humans could be exposed to through consumption. The research also indicated that passive samplers might prove useful as screening tools for those PFAS that bioconcentrate in fish but are below detection limits in water, and for screening short-chain PFAS that are efficiently eliminated from biota and not bioconcentrated.

This research was supported by the USGS Environmental Health and Water Quality Processes Programs with additional funding from the National Institute for Environmental Health award number P42ES027706.