Control of the Methylation process in a mercury-polluted aquatic sediment

Past refining activity deposited up to 1000 mg kg⁻¹ total mercury (Hg) in sediments of the estuarine Berry's Creek (New Jersey, USA), yet methylmercury levels in the sediment were below 10 μg kg⁻¹. The factors that control Hg methylation in this low-sality anaerobic sediment were analysed. When compared to a normally methylating control sediment, no significant differences were found in pH, E_h, microbial counts and methylating potential, but sulphide concentrations in Berry's Creek sediment were found to be unusually high. A causal connection between the elevated sulphide levels and low Hg methylation activity was established. In its current state, the contaminant poses little danger to biota, but a significant decline in sediment sulphide would be expected to increase the methylation and the biohazard of Hg. Should a site cleanup by dredging become necessary in the future, the contaminated dredge spoils should be prevented from weathering and should be speedily entombed in an anoxic sulphide-rich environment.