Microbial Methylation of Mercury in Wetlands and Its Environmental Risks

Abstract

Global mercury contamination presents a substantial threat to ecosystems and human health, primarily due to the conversion of inorganic mercury from anthropogenic sources into methylmercury by microorganisms in the environment. Wetlands are especially prone to this transformation due to their anaerobic conditions, abundant organic matter, and the prevalence of metal-reducing bacteria. This chapter explores the mechanisms of inorganic mercury methylation and the subsequent diffusion and accumulation of methylmercury in organisms and ecosystems, using a case study of mercury contamination in the Santa Lucia River wetlands in Uruguay. In this case, high concentrations of mercury were detected in the sediments over a 15,000 square meter area, exceeding regulated limits. The contamination was linked to the discharge of untreated wastewater containing inorganic mercury from a chlor-alkali plant. Although a wastewater treatment system was later installed, significant mercury contamination and hotspots persisted in the wetlands. These areas contained methylmercury in both the sediments and the biota, including reeds, shellfish, earthworms, and fish. Microbial analysis revealed the presence of Geobacter sulfurreducens and Geobacter metallireducens, bacteria known to methylate inorganic mercury. The existence of these microbial communities in areas of high mercury contamination poses serious risks at four levels to public health and ecosystems due to ongoing in situ methylation.

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Identifiers

DOI

10.5772/intechopen.1008767

Journal

Heavy Metals in the Environment - Contamination, Risk, and Remediation

Year

2025