Mercury and methylmercury in aquatic sediment across western North America

Abstract

Large-scale assessments are valuable in identifying primary factors controlling total mercury (THg) and monomethyl mercury (MeHg) concentrations, and distribution in aquatic ecosystems. Bed sediment THg and MeHg concentrations were compiled for >16,000 samples collected from aquatic habitats throughout the West between 1965 and 2013. The influence of aquatic feature type (canals, estuaries, lakes, and streams), and environmental setting (agriculture, forest, open-water, range, wetland, and urban) on THg and MeHg concentrations was examined. THg concentrations were highest in lake (29.3±6.5μgkg(-1)) and canal (28.6±6.9μgkg(-1)) sites, and lowest in stream (20.7±4.6μgkg(-1)) and estuarine (23.6±5.6μgkg(-1)) sites, which was partially a result of differences in grain size related to hydrologic gradients. By environmental setting, open-water (36.8±2.2μgkg(-1)) and forested (32.0±2.7μgkg(-1)) sites generally had the highest THg concentrations, followed by wetland sites (28.9±1.7μgkg(-1)), rangeland (25.5±1.5μgkg(-1)), agriculture (23.4±2.0μgkg(-1)), and urban (22.7±2.1μgkg(-1)) sites. MeHg concentrations also were highest in lakes (0.55±0.05μgkg(-1)) and canals (0.54±0.11μgkg(-1)), but, in contrast to THg, MeHg concentrations were lowest in open-water sites (0.22±0.03μgkg(-1)). The median percent MeHg (relative to THg) for the western region was 0.7%, indicating an overall low methylation efficiency; however, a significant subset of data (n>100) had percentages that represent elevated methylation efficiency (>6%). MeHg concentrations were weakly correlated with THg (r(2)=0.25) across western North America. Overall, these results highlight the large spatial variability in sediment THg and MeHg concentrations throughout western North America and underscore the important roles that landscape and land-use characteristics have on the MeHg cycle.

Biotic formation of methylmercury: A bio–physico–chemical conundrum

“…The chemical behaviors of the different chemical forms of Hg (i.e., Hg 0 , Hg II , CH 3 Hg I and (CH 3 ) 2 Hg) play critical roles in the biogeochemical cycling of Hg. Hg 0 allows for long‐range transport (Jackson ; Pirrone et al ), Hg II is the dominant reservoir for Hg in soils and aquatic systems (Fleck et al ; Eklöf et al ), and MMHg is bioconcentrated and biomagnified in aquatic food webs, reaching up to 80–100% of the total‐Hg (THg) measured in fish muscle (Bloom ; Mason et al ; Bravo et al ). As a consequence, MMHg exposure through fish consumption is of special concern for human health.…”

Methylmercury in Industrial Harbor Sediments in Taiwan: First Observations on Its Occurrence, Distribution, and Measurement

“…The MeHg ratio is mainly determined by the activities of microorganism relatively for methylation and demethylation and the proportion of bioavailable inorganic Hg in the sediments. However, determining the net rate of methylation and demethylation processes includes a network of biogeochemical reactions and environmental conditions [26,45]. The main factors affecting the Hg methylation are numerous and complex, including microorganisms, sulfide, organic matter, iron, selenium, pH, temperature, drying and wetting cycles, the age of Hg, redox stations, and salinity.…”

Mercury geochemistry and microbial diversity in meromictic Glacier Lake, Jamesville, NY

“…To assess the depths with highest potential for methylation, we calculated the %MeHg (the portion of total Hg present as MeHg), which has been used as an indicator for methylation efficiency (Fleck et al 2016). %MeHg reached a maximum of 56.6% in the chemocline (11 m depth) and was lowest in the monimolimnion (5%-11%).…”