Integrated evaluation of mercury speciation and composition of biofilms from the Tapajós River

Abstract

As a result of anthropogenic activities, Hg presents specific challenges not only in terms of human exposure but also in terms of environmental management. This is due to the bioaccumulation, biomagnification, and toxicity of Hg. The dispersion of Hg is independent of the place of emission, making it a global problem. Biofilms play an important role in Hg's bioaccumulation, bioamplification, and toxicity, contributing to its incorporation into freshwater food webs. However, the kinetics of Hg accumulation by biofilms is poorly described and understood. In this sense, the study aims to evaluate Hg contamination and its environmental impact in the Amazon region due to mining through the determination of THg and its species (IHg and MeHg) in the water and the biofilm obtained from the Tapajós River. In particular, biofilm characterization will clarify the impact of MeHg on biota (algae, bacteria, and fungi). Mercury methylation is mediated by microorganisms, yet little is known about potential microbial mechanisms for mercury detoxification. We will use biofilms to identify microbial indicators of Hg pollution and will analyze the distribution of genes involved in Hg reduction (merA) and demethylation (merB). Genes involved in the methylation process (hgcAB) will be also determined. These essays have direct and important implications for understanding the transformation of Hg and its bioavailability in the river ecosystem, monitoring local Hg, and expanding global knowledge about the diversity of associations of microorganisms in aquatic environments that contribute to the formation of MeHg and their biomagnification.