Mercury biomagnification and microbial adaptation in a mining-impacted Amazonian River

Area of Science:

• Environmental Science
• Microbiology
• Ecotoxicology

Background:

• Artisanal and small-scale gold mining (ASGM) releases mercury (Hg) into Amazonian ecosystems.
• The environmental fate of Hg in remote areas like the Caquetá River is poorly understood.
• Hg pollution poses risks to ecological integrity and public health, especially for Indigenous communities.

Purpose of the Study:

• To investigate Hg concentrations and microbial community responses in the Caquetá River.
• To assess the association between Hg levels, the merA gene, and microbial shifts.
• To identify potential Hg bioremediation strategies using native bacteria.

Main Methods:

• Measured Hg concentrations in soil, water, and fish samples along a river transect.
• Analyzed the abundance of the mercury-reductase gene (merA) in microbial communities.
• Assessed bacterial diversity and identified Hg-tolerant taxa.

Main Results:

• Hg concentrations in soil, water, and fish exceeded safety thresholds, indicating widespread contamination.
• Carnivorous fish showed particularly high Hg levels, suggesting food chain transfer.
• Elevated Hg levels were observed even at non-mining sites, pointing to downstream transport.
• Bacterial diversity correlated with Hg concentration, with increased abundance of merA and specific bacterial groups (Alphaproteobacteria, Acidobacteriia, Ktedonobacteria, Actinobacteria) in contaminated areas.
• Native Hg-resistant bacteria, such as Acinetobacter spp., were isolated.

Conclusions:

• The Caquetá River is significantly contaminated with mercury, posing health risks through fish consumption.
• Microbial communities play a role in Hg speciation and mobility, with specific bacteria adapting to Hg-rich environments.
• Hg-resistant bacteria show potential for bioremediation applications in contaminated Amazonian ecosystems.