Mercury in soils impacted by alluvial gold mining in the Peruvian Amazon

Area of Science:

• Environmental Science
• Geochemistry
• Ecotoxicology

Background:

• Gold mining is a primary global source of mercury (Hg) pollution, particularly in the Peruvian Amazon, causing significant environmental degradation and health risks.
• Alluvial gold mining in Peru releases an estimated 180 metric tons of Hg annually, impacting local ecosystems and food chains.

Purpose of the Study:

• To assess soil mercury (Hg) levels in abandoned alluvial gold mine spoils and adjacent undisturbed forests in Peru's Madre de Dios region.
• To compare Hg concentrations between Minimally Mechanized Mining (MMM) and Highly Mechanized Mining (HMM) sites and identify factors influencing Hg distribution.

Main Methods:

• Collected 162 soil samples (0-20cm depth) from MMM and HMM mine spoils and undisturbed forest sites.
• Conducted physicochemical analyses and determined Hg concentrations in all soil samples.
• Utilized statistical analysis to identify variables explaining soil Hg variations.

Main Results:

• No soil samples exceeded established environmental quality standards for Hg.
• Hg levels did not significantly differ between MMM and HMM sites.
• Vegetation cover, soil organic matter, pH, and clay content were key factors influencing soil Hg concentrations, explaining up to 80% of the variation.
• Unexpectedly, higher Hg concentrations were observed in bordering old-growth forests and with increasing vegetation regeneration on mine spoils.

Conclusions:

• Soil Hg concentrations in abandoned alluvial gold mine spoils are generally low, supporting land restoration and sustainable land use initiatives.
• Despite low levels in spoils, the continued use of Hg in mining operations poses significant human and environmental risks and must be urgently addressed.