Activated Carbon and Biochar Reduce Mercury Methylation Potentials in Aquatic Sediments

Much of the toxic methylmercury (MeHg) that biomagnifies in the aquatic food chain and accumulates in fish and seafood is believed to originate from microbial methylation of inorganic Hg(+2) in anoxic sediments. We examined the effect amending wetland sediments with activated carbon and biochar on Hg methylation potentials using microcosms and Hg stable isotope tracers. The inorganic (200)Hg(+2) spike was methylated at ~0.37 %/day in the untreated sediment, but that rate decreased to <0.08 %/day for the amended sediments, with 80 % and 88 % reductions in methylation rates for activated carbon and biochar amendments, respectively. Demethylation rates were relatively unchanged. Our key finding is that amending contaminated sediment with activated carbon and biochar decreases bioavailable Hg, and thus may also decrease Hg transfer into food webs. However, further research is needed to evaluate exactly how the sorbents impact Hg methylation rates and for related field studies.