How Climate Change Is Reawakening Mercury Pollution

In 2024, floodwaters tore through communities in southern Brazil, displacing more than 600,000 residents. These communities had survived storms before, but this storm destroyed homes and forced families onto rooftops. The death toll reached 183. There was widespread environmental devastation.

When the water finally receded, it left behind the usual wreckage: mud, debris, ruined crops. Less visible were the toxic metals like mercury the floodwaters had churned up, washing them from contaminated soils into rivers and carrying them into the Guaíba System, which supplies drinking water to more than two million people.

As climate change continues to intensify, aggravating extreme weather events such as floods and storms, the environmental and public health challenges posed by toxic metals and other pollutants are expected to become increasingly severe, with far-reaching consequences for ecosystems, food webs, and human communities, particularly those that are socioeconomically vulnerable. Mercury pollution represents a significant and growing concern, underscoring the urgent need to reduce greenhouse gas emissions that drive climate change. At the same time, it highlights the importance of strengthening regional and international cooperative frameworks to prevent, monitor, and mitigate mercury contamination.

Mercury is not new to the environment. It’s a naturally occurring element that cycles through Earth’s systems—land, atmosphere, and water—and has done so for millennia. The problem is that industrialization has radically accelerated that cycle. Coal plants, smelters, and, above all, artisanal and small-scale gold mining release far more mercury into the environment than the environment can absorb.

Once released, mercury can travel far from its original source. Drop mercury into a river in the Amazon or Congo, and some of it may move downstream with the flow, while some binds to sediment, organic matter, and tiny particles, settling in riverbeds, wetlands, and/or estuaries, where it may remain for long periods or be stirred back into the water during floods and storms.

Rivers are now the largest source of mercury in coastal oceans, delivering more than 1,000 tons annually, more than three times the amount the atmosphere deposits on the global coastal ocean surface. The Amazon River, the world’s largest river by discharge, accounts for over 20 percent of this riverine mercury delivery to the coastal ocean. Once in the ocean, mercury doesn’t just sit idle; it interacts with the water, atmosphere, seafloor, and marine life, posing potential risks to people.

Under certain conditions, microbes can convert mercury into methylmercury, the toxic form that enters aquatic food webs. The World Health Organization has long identified methylmercury as a neurological and developmental hazard, particularly for pregnant women and young children. It is estimated that up to 60,000 children born each year in the United States may face subtle neurological risks from maternal methylmercury exposure during pregnancy. Methylmercury accumulates in organisms at the base of aquatic food webs and becomes increasingly concentrated as it moves through fish, birds, and humans who depend on seafood for food. Even small increases in methylmercury production can lead to higher concentrations in fish commonly consumed by people. This poses a threat to food security, particularly for the more than 40 percent of the world’s population that relies on wild-caught and farmed seafood as a major source of animal protein.

Communities in developing countries are at the greatest risk of increased exposure to mercury from gold mining. Across the Amazon basin and parts of Africa, drought, economic desperation, and unreliable rainfall have pushed more people toward informal gold mining, where mercury is used to cheaply separate gold from sediment. Though its use is restricted or regulated in many countries, in remote mining areas, enforcement is limited and mercury can still be traded, used, and released into the environment with limited oversight.

The Minamata Convention on Mercury, adopted in 2013, was intended to address global mercury pollution. Named after the Japanese city devastated by industrial mercury poisoning in the 1950s and 1960s, the treaty aimed to reduce emissions globally and phase out the worst uses. Significant progress has been made, but a global network of public health advocates argues that the convention has failed to keep pace with the surge in artisanal gold mining.

And now, climate change is accelerating the damage, altering how mercury moves through rivers, waterways, and oceans; and affecting the conditions under which methylmercury is produced. Research shows that warming temperatures and more intense storms can disrupt sediments and wetlands that have long served as mercury’s resting places, effectively reactivating contamination buried for decades. When it floods, water is not the only thing moving; mercury and other toxic metals can be washed from soils, riverbanks, and mining areas into rivers and adjacent seas. As more mercury enters aquatic systems, changes in oxygen levels, warming waters, and shifts in marine food webs can affect where methylmercury is produced, how it is transported, and how much accumulates in seafood.

Efforts to reduce mercury pollution face regulatory, political, and economic challenges, raising concerns that progress could slow or even be reversed. Global coal demand remains near record levels in several regions, shaped by electricity demand, fuel prices, energy security concerns, and geopolitical pressures. Because coal combustion is an important source of atmospheric mercury, continued reliance on coal could make mercury reductions harder to achieve, especially where pollution controls are weak or enforcement is limited.

Reducing mercury exposure will require stronger enforcement of restrictions on mercury use in artisanal and small-scale gold mining; a transition from coal-fired power generation to cleaner, renewable energy sources; and the installation of emission-control technologies, such as activated carbon injection, in power plant exhaust systems. Proper collection, treatment, and disposal of mercury-containing waste are also essential. These measures can reduce the amount of mercury entering the environment and the food chain, thereby protecting millions of people worldwide from mercury-related health risks. Meeting this challenge requires cross-border and cross-sector cooperation to reduce mercury emissions, strengthen monitoring, and protect vulnerable communities. Limiting mercury’s renewed threat also depends on confronting climate change, which is intensifying floods, erosion, storms, and warming conditions, allowing rivers to remobilize mercury, transport it from land to the ocean, and increase exposure through aquatic food webs.

Roland Ovbiebo is a PhD candidate in oceanography at the UC San Diego Scripps Institution of Oceanography and a 2025-2026 IGCC Dissertation Fellow.

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