Ecotoxicological Assessment of Perfluorooctane Sulfonate and Perfluorooctanoic Acid Following Biodegradation: Insights from Daphnia magna Toxicity and Yeast Estrogen Screen Assays

Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) pose significant health risks through various exposure pathways, including ingestion of contaminated food and water, as well as dermal absorption. Aquatic organisms are especially at risk, as water bodies serve as primary pathways for the transport and transformation of these chemicals. While the biodegradation study was previously performed using a bacterial consortium from the activated sludge compartment at Zeekoegat WWTP, the ecotoxicological implications of the treated effluents remained unclear, particularly given the potential presence of degradation products. To address this gap, the present study used bioassays to evaluate the acute toxicity and endocrine-disrupting potential of PFOS and PFOA. For this purpose, PFOS and PFOA concentrations ranged from 58 ng/L to 1050 ng/L, and two types of bioassays were used: the Daphnia magna acute toxicity test, which examined the short-term lethal effects of the samples on a small freshwater organism (Daphnia magna), and the Yeast Estrogen Screen (YES), which measured estrogenic activity, an important indicator of potential endocrine disruption. Results revealed detectable estrogenic activity at environmentally relevant concentrations, with PFOS showing higher activity than PFOA. The estradiol equivalency (EEQ) values in samples containing PFOA ranged from 0.23 ± 0.029 ng/L to 3.15 ± 0.056 ng/L and from 0.43 ± 0.036 ng/L to 1.96 ± 0.086 ng/L in samples containing PFOS. Daphnia magna bioassays showed 100% mortality in samples containing PFOS at concentrations ≥ 62 ng/L and in samples containing PFOA at concentrations ≥ 142 ng/L, classifying them as ‘Very High Acute Hazard’ falling into Hazard Class V (100% mortality) according to the classification system proposed in 2003 by Persoone and co-workers. These bioassays helped to determine whether the degradation products were more toxic compared to the parent compounds, thereby supporting the objective of this study to assess environmental safety post-treatment.