Garimpo: Mercury Pollutants and Health Threats

Illegal gold mining, or garimpo, is a major environmental and public health issue, particularly in the Amazon. The use of mercury to extract gold contaminates ecosystems, endangering wildlife and human populations. This pollution persists long after mining operations cease, impacting communities reliant on local water sources and food chains.

Understanding how mercury spreads through the environment and accumulates in living organisms is crucial to assessing its risks.

Mercury Usage In Garimpo

Gold extraction in garimpo relies on mercury, which forms an amalgam with gold, allowing miners to separate the metal from sediment. This method, while inexpensive, results in significant mercury release. Artisanal and small-scale miners mix liquid mercury with gold-bearing soil or sediment, forming a soft alloy. To extract the gold, they heat the amalgam, vaporizing the mercury and releasing it into the air and water.

Mercury vapor poses an immediate hazard to miners and nearby communities. Inhalation can cause neurological damage, respiratory distress, and kidney dysfunction. Studies show miners exposed to mercury exhibit tremors, cognitive impairment, and motor dysfunction, with prolonged exposure leading to irreversible damage. The World Health Organization (WHO) identifies mercury as a toxic substance with no safe level of exposure.

Beyond airborne contamination, mercury discarded into waterways binds to organic matter and sediments, spreading downstream. This affects aquatic ecosystems and communities that rely on these water sources for drinking, fishing, and agriculture. Mercury persists in sediments for decades, continuously leaching into water systems even after mining ceases.

Chemical Residues In Mining Areas

The environmental impact of garimpo extends beyond mercury contamination. Mining sites accumulate heavy metals such as lead, arsenic, and cadmium, which infiltrate soil and water systems. Acid mine drainage, caused by sulfide minerals reacting with air and water, accelerates the spread of these toxic elements.

These residues interact with organic and inorganic materials, influencing their mobility. In acidic conditions, metals dissolve more readily, contaminating groundwater and surface water. Even in neutral conditions, periodic shifts in pH—triggered by rainfall, deforestation, or microbial activity—can remobilize trapped contaminants, reintroducing them into the water.

Agricultural communities near mining areas face risks as contaminated soil affects crop yields and food safety. Plants grown in metal-laden soils absorb toxic elements, leading to dietary exposure. In regions with high arsenic concentrations, rice cultivation becomes hazardous, as the plant readily absorbs arsenic. Chronic consumption of contaminated food has been linked to cancer, cardiovascular disease, and developmental disorders.

Methylation Of Heavy Metals

Once mercury settles in aquatic environments, it undergoes biochemical transformations that increase its toxicity. Methylation, primarily driven by anaerobic microorganisms, converts inorganic mercury into methylmercury—a highly toxic compound. These microbes, thriving in low-oxygen conditions in riverbeds and wetlands, attach a methyl group to mercury, enhancing its ability to infiltrate biological systems.

Methylmercury readily crosses biological membranes, allowing it to accumulate in organisms at every trophic level. Aquatic systems, particularly those with stagnant or slow-moving waters, provide ideal conditions for this process. The compound binds with proteins, especially sulfhydryl groups in enzymes and cells, leading to prolonged retention in biological tissues. Predators at the top of the food chain experience the highest concentrations due to biomagnification.

Bioaccumulation In Aquatic Systems

Methylmercury does not remain evenly distributed in water but binds to organic particles and plankton, entering the food web. Algae and zooplankton absorb it, accumulating the toxin in their tissues. Unlike many contaminants that can be excreted, methylmercury binds to proteins, leading to long-term retention.

Predatory fish, such as piranhas, catfish, and peacock bass in the Amazon, consume contaminated organisms, increasing mercury levels in their bodies. Since methylmercury has a biological half-life of weeks to months, it accumulates faster than it can be eliminated. Larger and longer-lived species contain the highest concentrations, making them particularly hazardous for human consumption. Studies show top predators often exceed safe mercury consumption limits established by the WHO, posing risks to fishing communities.

Mercury Pathways In Humans

Human exposure to mercury occurs primarily through diet and inhalation. In garimpo-affected regions, mercury-contaminated fish serve as the primary route of exposure. Once ingested, methylmercury binds to proteins and enters the bloodstream. Unlike inorganic mercury, it crosses biological barriers, including the blood-brain barrier and placenta, making it particularly hazardous for fetal and child development.

Prolonged exposure has been linked to cognitive deficits, motor impairments, and sensory disturbances. Studies in Amazonian communities show frequent fish consumption correlates with neurological symptoms, including memory loss, coordination issues, and speech difficulties. The Minamata disaster in Japan demonstrated the severe consequences of chronic exposure, with affected individuals suffering from tremors, vision impairment, and, in extreme cases, paralysis. Pregnant women are especially vulnerable, as mercury disrupts neurodevelopment, increasing the risk of intellectual disabilities and motor dysfunction in children.

Inhalation of mercury vapor primarily affects miners and those near processing sites. When mercury is burned to extract gold, toxic fumes are released and rapidly absorbed in the lungs, causing respiratory distress, headaches, and nausea. Long-term inhalation is linked to kidney damage and central nervous system disorders. Given mercury’s persistence in the environment and its ability to bioaccumulate, communities near mining areas continue to face health risks even after mining ceases. The long half-life of methylmercury in the human body—ranging from 50 to 70 days—complicates detoxification, as continuous exposure leads to progressively higher internal concentrations, worsening health effects over time.