Mercury and CO₂ emissions from artisanal gold mining in Brazilian Amazon rainforest

The Tapajós River basin in Brazil is one of the world's regions most affected by artisanal gold mining (ASGM), which is responsible for the release of mercury and high energy consumption. Mercury, mixed with gold-containing materials and then released through heating to extract the gold, can be recovered using a simple distillation device called a retort. Use of these tools has now become standard. In a comprehensive study, we investigated the use of mercury and energy at 47 mining sites in the Tapajós River basin. These included numerous mines that were operated informally or in some cases even illegally and are therefore not accessible to outsiders. Our survey shows that 1.7 kg of mercury are used per kg of gold extracted, of which only about 0.19 kg of mercury is released into the environment when retorts are used. Overall, this means an annual release of at least ≈2.5 tonnes of mercury in the region, even when retorts are used. We also find that ASGM contributes to climate change through energy consumption responsible for the release of about 16,000 kg of CO₂ equivalent per kilogram of gold. This means that even artisanal gold mining, which uses retorts, has a major environmental impact.