Critical review of mercury methylation and methylmercury demethylation rate constants in aquatic sediments for biogeochemical modeling

Mercury is a toxin that causes neurological impairments in adults, particularly harmful for fetuses and children, deadly severe cases, making it worldwide health concern. Methylmercury (MeHg) the environmentally relevant form of mercury (Hg) because biomagnifies along food chain. mainly produced aquatic sediments via methylation inorganic Hg (Hg(II)) transformed back demethylation. Because transformation rates determine MeHg concentrations, quantification demethylation needed to inform management MeHg. Published rate constants Hg(II) (km) (kd) vary greatly, stemming partly from differences experimental methods. We conducted comprehensive review laws, evaluated published constants, performed biogeochemical simulations assess variability reported km kd. Based on selected studies employing same pseudo-first-order law similar methods, we found km=0.04±0.03 d?1 reasonable range wetland sediments. Over number environments, maximum kd was smaller at sites without source (kd=0.5 d?1) than with identified (kd=1.8 d?1). Larger higher uncertainty compared highlight need more research rates. This critical review: (a) aids design future kd; (b) provides guidance comparing different studies; (c) presents reaction model constants; (d) informs selection values literature use simulations.