This type of artisanal mining is an important source of income for local people, supporting people in regions where jobs are limited. Similar mining methods were employed during the California gold rush in the mid-1800s. Yet artisanal gold mining is generally illegal, with little regulation. Efforts for formalizing this activity are ongoing but thus far have been limited.
Gold mining causes deforestation, which converts forests to polluted ponds and mobilizes large amounts of sediment from river bottoms. The burning of the gold-mercury amalgam also emits enormous quantities of mercury into the atmosphere. Artisanal gold mining currently contributes more than 35 percent of all global mercury emissions created by people, more so than any industrial activity. Once mercury enters the environment, it can cause neurological damage in both people and wildlife. In fact, numerous studies have found that people—especially indigenous communities—consuming fish caught near gold mining have elevated levels of mercury. Scientists are currently studying the health effects of high mercury exposure in people.
Once mercury is emitted into the atmosphere, it can enter a forest via three different pathways. First, mercury can dissolve in rainwater and then fall to the forest floor during rain events. Second, mercury can stick to the surface of small particles in the atmosphere. These particles can be intercepted by leaves, creating a coating of mercury on the leaves that can be washed to the forest floor during rain events in a process known as throughfall. And third, mercury can be taken up by leaves when their stomata are open for photosynthetic exchange of oxygen and carbon dioxide. This mercury can then enter the forest floor when the leaves drop.
Not only are these intact and protected forests receiving high mercury inputs, but they also hold large quantities of this mercury within their soils. Within the soils, microbes metabolize the elemental mercury into a methylated form of mercury that can enter the food web and is toxic to humans and animals. We found that songbirds in forests near gold mining sites have two to 12 times higher mercury concentrations in their bodies than songbirds living further away. These birds receive mercury from the fruit and insects that they eat, which in turn receive the mercury from the soil. These elevated levels of mercury in birds could decrease reproductive success, impair development, alter behavior and increase mortality.
Because of the danger mercury poses, the international community adopted the Minamata Convention on Mercury in 2017; it now has 132 countries as signatories. Article 7 specifically focuses on mercury releases from artisanal and small-scale gold mining, and many efforts are currently being undertaken by groups including the United Nations Environment Program (UNEP), United Nations Industrial Development Organization (UNIDO) and nongovernmental organizations to assist communities in meeting these targets.
In addition, we must increase our efforts to reduce mercury release from artisanal gold mining, especially near intact old-growth forests. Mercury-capture systems for artisanal gold mining and mercury-free systems are promising. But with any effort to reduce mercury release comes the need to provide investments and policies to ensure that people who rely on artisanal gold mining to support their livelihoods can do so without deleterious impacts to human and environmental health.
Importantly, we must look to local communities and local organizations who are familiar with the socioeconomic context to help drive needed changes to provide a better future for forests and the people that depend on them.
