Formation of artifact methylmercury during extraction from a sediment reference material

Area of Science:

• Environmental Chemistry
• Geochemistry
• Mercury Biogeochemistry

Background:

• Monomethylmercury (MMHg) is a potent neurotoxin, and understanding its formation is crucial for environmental risk assessment.
• Sediments are key reservoirs and transformation sites for mercury in aquatic ecosystems.
• Abiotic methylation of inorganic mercury is a significant pathway for MMHg production.

Purpose of the Study:

• To investigate the formation of artifact MMHg during the analysis of sediment reference material IAEA-405 and Long Island Sound sediments.
• To determine the factors controlling abiotic mercury methylation, specifically the roles of reactive mercury (HgR) availability and solution acidity.
• To assess the potential for abiotic mercury methylation in environmental settings.

Main Methods:

• Extraction of MMHg and reactive mercury (HgR) from sediments using aqueous distillation and dilute nitric acid leaching.
• Addition of inorganic mercury to assess methylation potential in sediment extracts.
• Analysis of artifact MMHg formation in relation to leachate acidity and HgR concentration.

Main Results:

• Artifact MMHg was formed from both ambient and added inorganic mercury in IAEA-405 extracts.
• MMHg formation correlated linearly with HgR in acidic leachates (> 1.2 M), but was limited by HgR availability in less acidic solutions (0.5-1.2 M).
• Potassium chloride addition enhanced HgR extraction but did not affect artifact MMHg formation.

Conclusions:

• Abiotic mercury methylation potential is inherent in sediments.
• The availability of reactive mercury (HgR) is the primary factor controlling MMHg production under environmental conditions.
• Abiotic methylation is likely enhanced in environments with increased inorganic mercury reactivity, such as estuarine mixing zones.