The impacts of illegal gold mining in Brazil are enormous and can be traced in a long chain that affects nature, biodiversity, and human health.
The government and science are still understanding the extent of this damage, with the contribution of studies such as the one recently published in the journal Science of the Total Environment. The research, carried out in native and inactive gold mining areas of the country, calculated losses of 50% in carbon reserves; on the other hand, the concentration of mercury in the soil and water reached 70%.
## Research in different biomes
The analysis was conducted by a group of researchers from the University of São Paulo (USP) and the Federal University of São Paulo (Unifesp) in mines of the Amazon, the Cerrado, the Pantanal, and the Atlantic Forest. “Our goal was to assess the impact of mining on the geochemistry of Hg (mercury) and SOM (soil organic matter) in four Brazilian biomes,” write the study’s authors.
Artisanal gold mining is associated with deforestation of native vegetation, which impoverishes the soil and makes it more vulnerable to the release of carbon into the atmosphere, exacerbating the climate crisis. Miners introduce mercury to separate gold from the environment: the combination of these two metals forms a substance called amalgam, which is then burned (to extract pure gold) and the mercury residue is discharged into water and soil.
## Main problems of illegal gold mining
“Illegal gold mining generates two main problems: the emission of carbon dioxide, which contributes to the increase in greenhouse gases, and the greater availability of mercury in the soil, an extremely toxic pollutant that can enter the food chain,” highlights agronomist and lead author of the research, Matheus Bortolanza.
Among the biomes covered by the study, the Amazon and the Pantanal presented the highest impact factors, with high concentrations of mercury and carbon reserve losses. The researchers indicate that this is related to the climatic conditions of these regions.
## Acceleration of decomposition
In warmer and wetter climates, the decomposition of soil organic matter is accelerated, influencing the faster emission of greenhouse gases, such as carbon dioxide (CO2). With more exposed soils, these mining-affected areas tend to release more concentrated mercury, increasing the risk of water contamination, animals, and local populations.
“As mercury is more available in the soil, the possibility of any living organism accessing it is very high. So, the health risk and possibility of contamination are much higher,” explains Bortolanza.
To conduct the analysis, scientists mapped mining areas in four Brazilian municipalities, located in different biomes: Tucumã (PA), Poconé (MT), Colider (MT), and Descoberto (MG). Samples were collected in areas of 64 square meters and with a depth of up to 20 centimeters.
## Evaluation of carbon and mercury dynamics
The dynamics of carbon and mercury were evaluated in the dry and wet seasons of mining and grazing areas through a combination of spectroscopic, chemical, and thermogravimetric extraction.
On average, the analyzed soils showed a minimum loss of 3.5 tons of carbon in the biomes. “Considering the original forest and greater depths, the numbers could be gigantic,” says Matheus Bortolanza.
## Gold mining in Brazil
Gold mining is an activity with a long history in the country, dating back to the construction (and destruction) of territories throughout Brazil. The Minas Gerais region was one of the first frontiers of the activity, in the 17th century.
More recently, the North and Midwest regions concentrate a large part of mining operations, which are often carried out irregularly, disregarding the demarcation of Indigenous Lands and Conservation Units.
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