Microbial transformation of arsenic species in municipal landfill leachate

Abstract

The microbial transformation of arsenic species in municipal landfill leachate (MLL) was investigated with the objective to highlight arsenic transformation in the landfill system. Across the 43 day incubation in MLL, more than 90% arsenate (iAs V) was found to reduce to arsenite (iAs III) within 20 days, while iAs III was comparably stable although a fraction of iAs III was temporarily oxidated to iAs V in the first 3 days. Transformation of monomethylarsonic acid (MMA V) to dimethylarsinic acid (DMA V) in MLL was slow with only 5% MMA V methylated to DMA V after 43 days incubation. A portion of DMA V and MMA V in MLL was demonstrated to transform into thiol-organoarsenic and monomethylarsonous acid (MMA III), which were identified to include dimethyldithioarsinic acid (DMDTA V), dimethylmonothioarsinic acid (DMMTA V) and monomethyldithioarsonic acid (MMDTA V) by HPLC–ICPMS and LC–ESI-MS/MS. The microbial formation of DMDTA V, DMMTA V and MMDTA V is postulated to relate to hydrogen sulfide generated by bacteria in MLL. Differences in arsenic transformation in sterilised and non-sterilised MLLs demonstrate bacteria play a crucial role in arsenic transformation in the landfill body. This study reveals the complexity of arsenic speciation and highlights the potential risk of forming highly toxic thiol-organoarsenic and MMA III in the landfill environment.