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Ecotoxicological Assessment of Perfluorooctane Sulfonate and Perfluorooctanoic Acid Following Biodegradation: Insights from Daphnia magna Toxicity and Yeast Estrogen Screen Assays
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This study developed novel enzymatic approaches for PET degradation, engineering PETase variants with improved thermal stability and hydrolysis efficiency. The engineered enzymes demonstrate significantly faster PET breakdown than wild-type PETase, advancing the development of biological PET recycling processes.
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.
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This review evaluates the aquatic toxicity of six PFAS compounds — PFOA, PFOS, PFBA, PFBS, GenX, and ADONA — against standard freshwater organisms, finding that legacy long-chain PFAS (PFOA, PFOS) are generally more toxic than newer short-chain replacements, though data gaps on chronic and mixture effects prevent firm safety conclusions about the alternatives.
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Transcriptomic analysis revealed that the flame retardant TBOEP and the PFAS compound PFECHS each disrupt distinct endocrine pathways in Daphnia magna — suppressing moulting and reproduction respectively — yet both converge on Wnt signaling, a conserved developmental pathway. This matters for microplastic pollution research because plastic-associated chemicals like flame retardants and PFAS frequently co-occur with microplastics in aquatic environments and cause compounding endocrine disruption in sentinel invertebrate species.
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Researchers reviewed the environmental fate and toxicity of three long-chain PFAS compounds (PFNA, PFDA, PFUnDA) in fish, finding through computational gene ontology analysis that these chemicals disrupt insulin signaling, immune pathways, and growth hormone systems, with longer-chain variants likely posing greater toxicity despite less study.
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