Risk of chlorine dioxide as emerging contaminant during SARS-CoV-2 pandemic: enzyme, cardiac, and behavior effects on amphibian tadpoles

Abstract

Objective: The use of chlorine dioxide (ClO2) increased in the last year to prevent SARS-CoV-2 infection due to its use as disinfectant and therapeutic human treatments against viral infections. The absence of toxicological studies and sanitary regulation of this contaminant represents a serious threat to human and environmental health worldwide. The aim of this study was to evaluate the acute toxicity and sublethal effects of ClO2 on tadpoles of Trachycephalus typhonius, which is a common bioindicator species of contamination from aquatic ecosystems. Materials and methods: Median lethal concentration (LC50), the lowest-observed effect concentration (LOEC), and the no-observed effect concentration (NOEC) were performed. Acetylcholinesterase (AChE) and glutathione-S-transferase (GST) activities, swimming behavior parameters, and cardiac rhythm were estimated on tadpoles of concentrations ≤ LOEC exposed at 24 and 96 h. ANOVA and Dunnett’s post-hoc comparisons were performed to define treatments significance (p ≤ 0.05). Results: The LC50 of ClO2 was 4.17 mg L−1 (confidence limits: 3.73–4.66). In addition, NOEC and LOEC values were 1.56 and 3.12 mg L−1 ClO2, respectively, at 48 h. AChE and GST activities, swimming parameters, and heart rates increased in sublethal exposure of ClO2 (0.78–1.56 mg L−1) at 24 h. However, both enzyme activities and swimming parameters decreased, whereas heart rates increased at 96 h. Conclusion: Overall, this study determined that sublethal concentrations of ClO2 produced alterations on antioxidant systems, neurotoxicity reflected on swimming performances, and variations in cardiac rhythm on treated tadpoles. Thus, our findings highlighted the need for urgent monitoring of this chemical in the aquatic ecosystems. Graphical abstract: [Figure not available: see fulltext.]