Microbial generation of elemental mercury from dissolved methylmercury in seawater

Abstract

Elemental mercury (Hg0) formation from other mercury species in seawater results from photoreduction and microbial activity, leading to possible evasion from seawater to overlying air. Microbial conversion of monomethylmercury (MeHg) to Hg0 in seawater remains unquantified. A rapid radioassay method was developed using gamma‐emitting 203Hg as a tracer to evaluate Hg0 production from Hg(II) and MeHg in the low pM range. Bacterioplankton assemblages in Atlantic surface seawater and Long Island Sound water were found to rapidly produce Hg0, with production rate constants being directly related to bacterial biomass and independent of dissolved Hg(II) and MeHg concentrations. About 32% of Hg(II) and 19% of MeHg were converted to Hg0 in 4 d in Atlantic surface seawater containing low‐bacterial biomass, and in Long Island Sound water with higher bacterial biomass, 54% of Hg(II) and 8% of MeHg were transformed to Hg0. Decreasing temperatures from 24°C to 4°C reduced Hg0 production rates cell−1 from Hg(II) 3.3 times as much as from a MeHg source. Because Hg0 production rates were linearly related to microbial biomass and temperature, and microbial mercuric reductase was detected in our field samples, we inferred that microbial metabolic activities and enzymatic reactions primarily govern Hg0 formation in subsurface waters where light penetration is diminished.

Mercury Cycling in the North Pacific Subtropical Gyre as Revealed by Mercury Stable Isotope Ratios

“…The Δ 199 Hg values of surface (25 m) zooplankton display a clear diurnal pattern, where Δ 199 Hg values are greater during the day than at night, and their isotopic composition is significantly higher than deeper samples (125–1,250 m, Wilcoxon test, W = 15, p < 0.01). A diurnal cycle of Δ 199 Hg values in zooplankton is expected given the recent reports that marine phytoplankton and bacterioplankton can photochemically degrade Hg (Grégoire & Poulain, ; Kritee et al, ; Lee & Fisher, ). We suggest the Δ 199 Hg value in surface zooplankton represents the isotopic composition of photodegraded MMHg in phytoplankton or particle‐associated MMHg that has been photodemethylated before entering the food web.…”

Dark Reduction Drives Evasion of Mercury From the Ocean

“…This value, when combined with the flux information, suggests a residence time of Hg in the surface ocean with respect to evasion of about 0.76 years and an apparent specific net reduction rate of 0.36 % day −1 . This apparent specific reduction rate is slower than that measured for gross production of Hg 0 from Hg(II) (e.g., Rolfhus, 1998;Costa and Liss, 1999;Whalin et al, 2007;Fantozzi et al, 2009;Qureshi et al, 2010;Soerensen et al, 2014;Kuss et al, 2015;Lee and Fisher, 2019). If gross reduction proceeds faster than the loss of Hg 0 from the surface ocean, then there must be substantial re-oxidation of Hg 0 prior to evasion (e.g., Soerensen et al, 2010).…”

“…temperature using a Q 10 value of 2 (Lee and Fisher, 2019), and which is typical for biological processes. This term might also be expected to have other dependencies related to the activity of bacteria in a given location, including for example primary production.…”

Fluorescence Based Comparative Sensing Behavior of the Nano-Composites of SiO2 and TiO2 towards Toxic Hg2+ Ions

“…Additionally, as a consequence of processes such as chlor-alkali and gold mining add mercury into the nature. In addition, the inorganic mercury pollutants possess capability to absorb and transform into organic ones by bacteria and microbes [8][9][10][11][12]. The most abundant and stable forms of mercury present in nature, are in its +2 oxidation state.…”