Toxicological Response of Chironomus dilutus in Single Chemical and Binary Mixture Exposure Experiments with Six Perfluoralkyl Substances

By Christopher J McCarthy, Shaun A Roark, Demitria Wright, Kelly O'Neal, Brett Muckey, Mike Stanaway, Justin Rewerts, Jennifer Field, Todd Anderson, and Christopher J Salice
Environ Toxicol Chem
April 13, 2021
DOI: 10.1002/etc.5066

Few studies have determined the toxicity of perfluoralkyl substances to aquatic invertebrates. Here, we exposed Chironomus dilutus to six different perfluoroalkyl substances (PFAS) to assess single chemical toxicity and relative or proportional toxicity among substances. A 10 d range finding test was conducted to inform 20 d assays for the following PFAS: (perfluorooctane sulfonate [PFOS], perfluorooctanoic acid [PFOA], perfluorononanoic acid [PFNA], perfluorobutanesulfonic acid [PFBS], perfluorohexanesulfonic acid [PFHxS], and perfluoroheptanoic acid [PFHpA]). A 20 d binary mixture study of PFOS+PFHxS followed the single chemical tests. Measurement endpoints 20 d tests included larval survival and biomass. Log-logistic concentration response models were used to estimate 10, 20, and 50 percent effects concentrations for PFOS, PFHxS, and PFOA. Survival EC50s for PFOS, PFHxS, and PFOA were 2.49 µg/L, 913 µg/L, and 192,000 µg/L, respectively, while survival EC20s were 1.70 µg/L, 3,860 µg/L, 119,000 µg/L for PFOS, PFHxS, and PFOA respectively. Biomass as a combined survival and growth endpoint resulted in EC20s of 1.89 µg/L, 896 µg/L, 137,000 µg/L for PFOS, PFHxS, and PFOA, respectively. Maximum concentrations tested (NOECs) for PFNA, PFBS, and PFHpA were two to three orders of magnitude greater than the PFOS EC50s and showed no toxicity to C. dilutus, even at exposure concentrations well above what would be considered environmentally relevant. The binary mixture of 2.5 ug/L PFOS+1,000ug/L PFHxS showed reduced survival compared to controls and some indication of potential additive or synergistic interaction between PFOS and PFHxS. Overall, this study supports previous studies showing PFOS to be the most toxic PFAS to aquatic life and suggests that PFOS could be more toxic to freshwater midge than previously reported. This article is protected by copyright. All rights reserved.

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