Bioaccumulation and biotransformation of hexavalent chromium in black soldier fly (Hermetia illucens) in the antagonism of selenate

As a global environmental pollutant, many studies have focused on the removal of hexavalent chromium [Cr(VI)] from industrial wastewater, using organic materials as adsorbents. This study investigated the potential of the black soldier fly (BSF) for the bioremediation of the Cr-adsorbing/containing wheat bran as an adsorbent and antagonistic effects of selenate [Se(VI)] on Cr accumulation/transformation by the BSF. Our results indicate the BSF could tolerate Cr/Se toxicity without exhibiting significant morphological changes. Cr/Se concentrations in the BSF biomass decreased over the life cycle, suggesting the detoxification of both contaminants, while relatively lower Cr but significantly higher Se concentrations were found in the larvae co-exposed to Cr and Se, compared with the Cr/Se-exposed only larvae. Low bioaccumulation factor (BAF) values (∼0.47) indicate the absorbed Cr tended to be excreted out. The XAS results suggest the accumulated Cr was mainly present as elemental chromium during growth, while the Se, potentially as an antagonist, was mainly converted to elemental selenium and organo-Se species (selenomethionine/selenocystine) in the BSF co-exposed to Cr and Se. Overall, our study provides a better understanding of the biotransformation of Cr(VI), with or without Se, by the BSF, and risks of using the Cr-containing BSF as feed.