Methylmercury production and distribution in aquatic systems

Area of Science:

• Environmental Chemistry
• Aquatic Toxicology
• Biogeochemistry

Background:

• Mercury contamination in aquatic ecosystems is a significant environmental concern.
• Methylmercury (MeHg) is a highly toxic form of mercury that bioaccumulates in food webs.
• Understanding mercury methylation and partitioning is crucial for assessing ecological risk.

Purpose of the Study:

• To investigate mercury methylation and partitioning dynamics in river sediment.
• To determine the influence of fish presence on mercury methylation and MeHg levels.
• To quantify mercury uptake rates and partition coefficients in fish.

Main Methods:

• River sediment was spiked with mercuric chloride at varying concentrations (1, 5, 10 ppm).
• Incubation experiments were conducted with and without fish to assess MeHg production and partitioning.
• Mercury concentrations in sediment, water, and fish were analyzed over time.

Main Results:

• Maximum methylmercury production occurred within the first week, reaching equilibrium in 3-4 weeks.
• Fish presence significantly increased equilibrium MeHg concentrations in sediment (15-32 ng/g) and water (1.5-5.5 ng/l) compared to controls (3-4.5 ng/g and 0.53 ng/l).
• Mercury concentration in fish increased exponentially, with uptake rates of 10-18 ng/g/day, and high partition coefficients (Kf-w) for MeHg (10,000-22,000).

Conclusions:

• Mercury methylation and partitioning are rapid processes in contaminated sediments.
• Fish significantly influence mercury methylation and MeHg accumulation in aquatic systems, though direct in vivo methylation by fish is not supported.
• These findings highlight the complex interactions in mercury cycling and bioaccumulation within aquatic environments.