Perfluoroalkyl substances (PFAS) are highly persistent, bioaccumulative and toxic to a wide range of aquatic organisms but currently the limited effects data impede risk assessments. While PFAS are known to accumulate in sediments, minimal information exists on the risks PFASs pose to benthic organisms. Here we assessed chronic toxicity to estuarine/marine benthic organisms of sediments artificially spiked with perfluorooctane sulfonic acid (PFOS) and to field-collected sediments contaminated with PFAS. No toxicity from PFOS occurred to benthic algae, copepod, or crab species in exposures with 170-180 mg/kg in spiked-sediments and 0.8-2 mg/L in the overlying waters. Toxicity of PFOS to amphipod survival and reproduction occurred and was attributed to dissolved rather than dietary exposure. The lowest dissolved PFOS concentrations causing toxicity were 0.28 mg/L (LOEC) to 28-day bivalve growth, 0.49 mg/L to survival and growth of juvenile amphipods, and 1.2 and 0.9 mg/L as a LOEC and LC10 values for 10-day amphipod reproduction, respectively. We note the experimental challenges in undertaking tests with PFAS.
A strong relationship existed for PFOS-partitioning between sediment and overlying water (Kd) concentrations and organic carbon (0.1 to 5.6% OC), with a Kd range of 16 to 150 L/kg. Considering all literature data for PFOS toxicity for benthic estuarine/marine organisms, 99% and 95% species protection concentrations of 6 and 25 µg/L were derived from a species sensitivity distribution (11 species, including results from the present study). A conservative Kd value of 10 was used to derive a benthic PC99 screening value of 60 µg/kg PFOS (for 1% OC) representing a low risk to benthic organisms in estuarine/marine environments from direct toxicity and secondary poisoning.
Field-collected sediments were dominated by PFOS, with 4-15 µg /kg (1% OC) at estuarine/marine sites, being below the screening value and chronic toxicity was not observed in benthic algae, amphipod, and copepod tests.