Artificial lake expansion amplifies mercury pollution from gold mining

Abstract

Artisanal and small-scale gold mining (ASGM) is the largest global source of anthropogenic mercury emissions. However, little is known about how effectively mercury released from ASGM is converted into the bioavailable form of methylmercury in ASGM-altered landscapes. Through examination of ASGM-impacted river basins in Peru, we show that lake area in heavily mined watersheds has increased by 670% between 1985 and 2018 and that lakes in this area convert mercury into methylmercury at net rates five to seven times greater than rivers. These results suggest that synergistic increases in lake area and mercury loading associated with ASGM are substantially increasing exposure risk for people and wildlife. Similarly, marked increases in lake area in other ASGM hot spots suggest that “hydroscape” (hydrological landscape) alteration is an important and previously unrecognized component of mercury risk from ASGM.

Amazon forests capture high levels of atmospheric mercury pollution from artisanal gold mining

“…Our data show that this Hg is available to, and moving through, terrestrial food webs. Moreover, very large quantities of Hg are stored in biomass and soils with the potential for release with land use change 4 and forest fires 45 , 46 . The southeastern Peruvian Amazon is one of the most biodiverse ecosystems on the planet for vertebrate and insect taxa 47 .…”

“…This form of gold mining occurs in over 70 countries, is frequently either informal or illegal, and accounts for approximately 20% of the world’s gold production 1 . While ASGM is an important livelihood for local communities, it results in widespread deforestation 2 , 3 , extensive conversion of forests to ponds 4 , high sediment loading in nearby rivers 5 , 6 , and is the largest global source of atmospheric mercury (Hg) emissions and freshwater Hg releases 7 . Many intensive ASGM sites are within global biodiversity hotspots and lead to decreased diversity 8 , loss of sensitive species 9 , and high exposure of Hg in both people 10 – 12 and top predators 13 , 14 .…”

Rapid changes to global river suspended sediment flux by humans

“…Many of these rivers lack suspended sediment observations during the period of interest, and some have no published suspended sediment data at all. Recent advances in computational resources ( 4 ) and digital archives of hydrologic data allow for improved analysis of satellite image archives to monitor global water quality ( 5 , 6 ). We capitalized on these advances to evaluate decadal changes to river suspended sediment concentration (SSC) and flux, using a suite of algorithms trained on more than 130,000 ground truth measurements from 340 diverse sites in North America, South America, and Taiwan ( 5 ).…”

Evaluating atmospheric mercury (Hg) uptake by vegetation in a chemistry-transport model

“…82 Increased exposure to Hg health risks may not be limited to marine ecosystems, since deforestation can increase Hg methylation rates in freshwater aquatic ecosystems. 83 Efforts to mitigate climate change and avoid deforestation will be crucial to avoid additional mobilization of Hg in the environment, meaning that the goals of the Minamata Convention intersect with other international treaties such as the Paris Climate Accords. 78 S2 †).…”