Ecotoxicological efficiency of Cr(VI) removal treatment with reductive biogenic iron-based material determined by amphibian larval bioassays

Abstract

Due to the toxic effects of chromium, its high environmental persistence, and potential for bioaccumulation, it is imperative to develop sustainable strategies for managing its contamination. In the present study, the synthesis time of supported biogenic iron-based microparticles (BioFe-MMT) and their performance in the Cr(VI) removal process were analyzed. Its lethal and sublethal ecotoxicological effects were subsequently evaluated through standardized bioassays using amphibian Rhinella arenarum larvae exposed to BioFe-MMT and Cr(VI) before and after the removal treatment. Results demonstrated that BioFe-MMT biosynthesized for 3 weeks had smaller particle size and better Cr(VI) and total Cr removal efficiency (>99% and >91%, respectively) compared to longer synthesis times. Ecotoxicological bioassays showed that Cr(VI) caused a significant increment of lethal toxicity to larvae with 50% Lethal Concentration (LC 50) at 96 and 504 h of 25.1 and 0.04 mg L⁻¹, respectively. Several sublethal effects were observed such as reduced body size, wavy and underdeveloped tail, and behavioral disorders. This toxicity could be explained by the Bioconcentration Factor (BCF) at 96 h, which was 12.26 L kg⁻¹. On the other hand, BioFe-MMT and the supernatant obtained after the treatment had negligible toxic effects. Larvae exposed to the sludge obtained after Cr(VI) removal treatment (Cr-BioFe-MMT) presented significant mortality from 216 h, which was explained by Cr(VI) desorption from the Cr-BioFe-MMT sludge. These results highlight the BioFe-MMT potential use in Cr(VI) removal due to its efficiency and the reduced toxicity of the treated solution.