Impact of El Niño on Environmental Mercury in Madre de Dios, Peru

Abstract

Studies show that concentrations of methylmercury in fish increase in association with flooding. Additionally, the southeastern Amazonian region of Peru, Madre de Dios (MDD), is seeing increased development of artisanal and small-scale gold mining (ASGM) and use of mercury to extract the gold. Mercury used in ASGM is released into the environment and methylated by anaerobic bacteria into a neurotoxin, methylmercury (MeHg), that can bioaccumulate in aquatic food chains. Our hypothesis is that due to increased flooding in MDD from El Niño, there will be greater amounts of bacterial activity in sediment that will lead to increased bio-methylation of mercury and biomagnification of MeHg in fish downstream of ASGM activity. Fish mercury concentrations were significantly higher among fish collected during the months of El Nino compared to non-El Nino months. During the non-El Niño year, 47 of 200 (24%) fish samples, and 39 of 123 (32%) carnivorous fish samples surpassed the World Health Organization mercury guideline of 0.5 mg/kg. During the El Niño year, 60 of 64 (94%) of fish samples, and 32 out of 36 (89%) of carnivorous fish samples surpassed the WHO standard. Precipitation, temperature, and soil moisture all had a significant impact on fish tissue mercury concentrations. Generally, precipitation, minimum temperature, and soil moisture increased mercury between 16 and 48 weeks before the date of collection. There was no significant difference between the non-El Niño and the El Niño years for suspended particulate mercury. Precipitation, temperature, and soil moisture all had a significant impact on particulate mercury concentrations. Precipitation and soil moisture increased mercury while maximum temperature decreased mercury between 3 and 15 weeks before the date of collection. This is one of the first studies to investigate the impact of El Niño on environmental mercury concentrations and find an increase in fish tissue mercury concentrations. This could represent a public health threat to communities where ASGM is prevalent, and extreme weather, such as El Niño, occurs. Additionally, this study defined specific meteorological factors that impact environmental mercury concentrations. Both these climate components and El Niño could become more extreme due to climate change.