Release of Methyl Mercury from Sediments: Effects of Mercury Concentration, Low Temperature, and Nutrient Addition

A flow-through system using plexiglass "microbasins" was used to study methyl mercury release from unpolluted, mercury polluted, and mercury enriched lake and river sediments. Production of methyl mercury ranged up to 3.3 μg∙m−2∙d−1, increasing with increasing mercury content as if following saturation kinetics. It leveled off when mercury content was 15–20 μg Hg/g. An equilibrium between methylating and demethylating mechanisms is suggested. Release at 4 °C was 50–70% of that at 20 °C, which suggests that in polluted Canadian lakes, production in winter may be half the total for the year. Increased methyl mercury release was observed when tryptic soy broth (TSB) was added to sediments at 0.06 or 0.25 g/dm3, and very marked increases when TSB was added to the water flow at 35 mg/L, suggesting an effect at the sediment–water interface.Key words: mercury, methyl mercury, methylation, microbasin, microorganism, sediments, biomethylation