Local intensity of artisanal gold mining drives mercury accumulation in neotropical oxbow lake fishes

Driven by surges in global gold prices and additional socio-economic factors, artisanal small-scale gold mining (ASGM) in the Global South is increasing and driving emissions of significant quantities of mercury (Hg) into the air and fresh-water. Hg can be toxic to animal and human populations and exacerbate the degradation of neotropical freshwater eco-systems. We examined drivers of Hg accumulation in fish that inhabit oxbow lakes of Peru's Madre de Dios, a region with high biodiversity value and increasing human populations that depend on ASGM. We hypothesized that fish Hg levels would be driven by local ASGM activities, by environmental Hg exposure, by water quality, and by fish tro-phic level. We sampled fish in 20 oxbow lakes spanning protected areas and areas subject to ASGM during the dry sea-son. Consistent with previous findings, Hg levels were positively associated with ASGM activities, and were higher in larger, carnivorous fish and where water had lower dissolved oxygen levels. In addition, we found a negative relation-ship between fish mercury levels associated with ASGM and the occurrence of the piscivorous giant otter. The link be-tween fine-scale quantification of spatial ASGM activity and Hg accumulation, as indicated by the result that in the lotic environment, localized effects of gold mining activities are stronger drivers (77 % model support) of Hg accumu-lation than environmental exposure (23 %) constitutes a novel contribution to a growing body of literature on Hg con-tamination. Our findings provide additional evidence of high Hg exposure risks to neotropical human and top carnivore populations subject to the impacts of ASGM, which depend on freshwater ecosystems undergoing gradual degradation. The documented spatial variation in Hg accumulation and increased Hg levels in carnivorous fish should serve as a warning to human communities in Madre de Dios to avoid the proximity of high-intensity gold mining areas and minimize local carnivorous fish consumption.

Automated summary

Driven by global gold price surges and additional socio-economic factors, artisanal small-scale gold mining (ASGM) in the Global South is increasing, resulting in significant mercury (Hg) emissions into the air and fresh-water. This study examined the factors influencing mercury accumulation in fish in oxbow lakes in Peru's Madre de Dios region and found that Hg levels were associated with ASGM activities, water quality, and fish trophic level. The results highlight the risks of high Hg exposure to human and top carnivore populations in neotropical ecosystems undergoing degradation due to ASGM.