Thiol-Based Selective Extraction Assay to Comparatively Assess Bioavailable Mercury in Sediments

Area of Science:

• Environmental Science
• Geochemistry
• Microbiology

Background:

• Methylmercury bioaccumulation in aquatic food webs is driven by mercury methylation by anaerobic microbes.
• In sulfidic environments, only a small fraction of mercury (Hg(II)) is bioavailable for methylation, making quantification challenging.
• Bioavailable mercury may include Hg(II) associated with solid phases like nanostructured mercuric sulfides.

Purpose of the Study:

• To develop and validate a thiol-based selective extraction assay for quantifying the bioavailable mercury fraction in sediments.
• To assess the correlation between GSH-leachable mercury and methylmercury concentrations in natural sediment samples.
• To evaluate the assay's performance in microcosm experiments with varying mercury bioavailability.

Main Methods:

• Developed a thiol-based assay using glutathione (GSH) to selectively leach mercury from sediment samples.
• Quantified GSH-leachable mercury in nine marine sediment samples.
• Applied the assay to anaerobic sediment slurry microcosm experiments with sediments amended with different mercury forms.

Main Results:

• A strong positive correlation (r²=0.91, p<0.0001) was observed between GSH-leachable mercury and methylmercury concentrations in marine sediments.
• In microcosm experiments, GSH-leachable mercury concentrations increased with methylmercury production, mirroring known bioavailability trends.
• The thiol-based method demonstrated improved assessment of mercury bioavailability compared to previous methods.

Conclusions:

• The thiol-based selective leaching assay provides a reliable measure of bioavailable mercury in sediments.
• This assay offers a valuable tool for assessing mercury methylation potential and comparing risks across different aquatic environments.
• The method advances our understanding of mercury speciation and bioavailability in sediment ecosystems.