Perfluorooctane sulfonate (PFOS) is an anthropogenic compound found in trace amounts in many environmental compartments far from areas of production. This, along with the highly persistent nature of PFOS, presents a concern for possible effects in aquatic ecosystems. The objective of this study was to determine the toxicity of PFOS in representative freshwater organisms. Toxicity testing using standard laboratory protocols was performed on the green algae Selenastrum capricornutum and Chlorella vulgaris, the floating macrophyte Lemna gibba, and the invertebrates Daphnia magna and Daphnia pulicaria. No observable effect concentration (NOEC) values were generated from the most sensitive endpoints for all organisms. Autotroph inhibition of growth NOEC values were 5.3, 8.2, and 6.6 mg/L for S. capricornutum, C. vulgaris, and L. gibba, respectively. The 48-h immobility NOEC values for D. magna and D. pulicaria were 0.8 and 13.6 mg/L, respectively. In comparison to immobility, the 21-day lethality NOEC for D. magna was 5.3 mg/L. Based on effect (immobility) values, the most sensitive of all test organisms was D. magna. The most sensitive organism based on 50% inhibition of growth (IC(50)) was L. gibba, with an IC(50) value of 31.1 mg/L determined from wet weight. This is 4.3 times less than the LC(50) for D. pulicaria, which was 134 mg/L. Significant adverse effects (p < or = 0.05) were observed for all organisms in concentrations >134 mg/L. The results indicate that under laboratory conditions PFOS is acutely toxic to freshwater organisms at concentrations at or near 100 mg/L. Based on known environmental concentrations of PFOS, which occur in the low ng/L to low microg/L range, there is no apparent risk to freshwater systems. However, further work is required to investigate long-term effects in these and other freshwater organisms.

Little is known regarding perfluorooctane sulfonic acid (PFOS) toxicity to freshwater organisms. This field evaluation aims to assess the toxicological risk associated with exposure to PFOS across levels of biological organization. The analysis of variance study was conducted in replicate (n = 3) 12,000 L outdoor microcosms. Multivariate techniques were used to assess the response of zooplankton community structure and dynamics, as well as a floating macrophyte, Lemna gibba. The zooplankton community was significantly affected (p < 0.05) by the treatment regime given by the Monte Carlo permutations for all sampling times. A community-level no-observable-effect concentration ([NOEC]community) of 3.0 mg/L was determined for the 35-day study, however, longer term studies are recommended. The most sensitive taxonomic groups, Cladocera and Copepoda, were virtually eliminated in 30 mg/L treatments after 7 d. The 42-d 50% inhibition concentration (IC50) for L. gibba frond number was 19.1 mg/L and the NOEC was 0.2 mg/L. Furthermore, we investigated the persistence of PFOS over 285 d in microcosms under natural conditions. Perfluorooctane sulfonic acid concentration showed no drastic reduction in any treatment microcosm over the entire study period, confirming that this compound undergoes little degradation in aquatic systems. Presently, there appears to be little hazard to these freshwater organisms at reported environmental concentrations.

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There is presently a substantial amount of information being gathered concerning the environmental risk associated with the perfluorooctane sulfonate (PFOS) compound. The U.S. Environmental Protection Agency (U.S. EPA) is requiring that more research be completed before making definitive decisions concerning the regulatory issues covered in the significant new use rule (18/10-2000) under the Toxic Substance Control Act. However, there are no risk assessment requirements under seminatural conditions in microcosms. The PFOS can enter, and has been found in, the aquatic environment through different pathways, including spills associated with use of fire-fighting foams containing PFOS, leaching from washing Scotchgard-treated clothes with the wastewater, leaching from various coatings, discharges as residual waste from fluorochemical production, or volatilization and transportation atmospherically. The biota is the sink of PFOS rather than the sediment or soil. The aim of this article is to determine a 35-d community no-observable-effect concentration (NOECcommunity) for freshwater zooplankton and the fate of PFOS during the course of study. The PFOS persisted in the water phase with only slight reductions over the study; only the decrease from 33.9 mg/L at day 1 to 29.8 mg/L at day 35 was significant. A 90 to 100% reduction (p < 0.01) of the total zooplankton population was found after one week of exposure to 30 mg PFOS/L and a similar reduction after two weeks at 10 mg PFOS/L. The Daphnia magna 21-d NOECsurvival of 12 mg/L has previously been found in a standard laboratory bioassay by 3M. The rank order of susceptibility for the test community was Copepoda > Cladocera > Rotifera, assuming all adverse direct effects.

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