Mercury levels in the world’s rivers have surged dramatically since the Industrial Revolution, with new research revealing a more than twofold increase in the amount of this toxic metal flowing through waterways globally. A study led by Tulane University, published on June 11, 2025, in Science Advances, establishes the first comprehensive global baseline for riverine mercury pollution, offering crucial insight into how human activities have reshaped the mercury cycle and raised risks to ecosystems and public health.
Before 1850, global rivers carried approximately 390 metric tons of mercury annually into the oceans. Today, that figure has jumped to about 1,000 metric tons per year, representing an increase of roughly 585 metric tons over two centuries. This dramatic rise is primarily driven by wastewater discharge, soil erosion, industrial waste, and mining operations, according to Yanxu Zhang, an associate professor at Tulane’s School of Science and Engineering and the study’s lead author.
“Human activities have disrupted the global mercury cycle in every aspect,” Zhang explained. “While previous studies have focused on mercury concentrations in the atmosphere, soils, and seawater, they have largely overlooked rivers, a major pathway for mercury that has effectively become a pipeline for wastewater from both municipal and industrial sources.” This disruption is particularly concerning because mercury is a potent neurotoxin that accumulates in fish and can move up the food chain, posing serious health risks to humans and wildlife alike.
The research team developed a sophisticated computer model called MOSART-Hg to simulate how mercury moves through river systems worldwide. Their findings closely matched mercury concentrations found in dated sediment core samples from coastal areas, validating their approach. The model reconstructed natural mercury emissions from pre-industrial sources such as volcanic activity and wildfires, establishing a baseline against which modern pollution can be measured.
Regional analysis revealed that North and South America have contributed the largest share—41%—of the global increase in riverine mercury since 1850. Southeast Asia and South Asia followed with 22% and 19%, respectively. In South America’s Amazon region, mercury levels now exceed 200 metric tons per year, with approximately three-quarters of this originating from human activities, primarily artisanal and small-scale gold mining (ASGM) and deforestation. “The Amazon River’s mercury budget now exceeds 200 metric tons per year, with three-quarters of this originating from human activities and primarily ASGM,” Zhang noted.
East Asia’s mercury pollution is mainly driven by industrial releases. Rivers in China alone contribute over 70% of the region’s mercury load, with the Yangtze River’s mercury flux having more than doubled since pre-industrial times. However, not all regions have seen increases; the Mediterranean area experienced a decline in mercury levels, attributed to dam constructions such as the Aswan High Dam on the Nile River, which trap mercury-laden sediment.
These findings carry significant implications for public health, especially for communities dependent on fish consumption. Mercury exposure can cause a range of neurological symptoms, including loss of peripheral vision, tingling sensations in extremities, and impairments in speech, hearing, and walking. The Environmental Protection Agency (EPA) warns that mercury exposure to infants in the womb can severely impact brain and nervous system development.
Despite the clear dangers, recent policy shifts in the United States threaten to exacerbate mercury pollution. Earlier this year, EPA Administrator Lee Zeldin launched a sweeping deregulation campaign targeting emissions standards, including revisions to the Mercury and Air Toxics Standards (MATS) that limit mercury and arsenic pollution from coal and oil power plants. The EPA described these rules as “overreaching” in a March press release.
At a press conference on June 11, 2025, Zeldin assured that if the proposed changes to MATS are finalized, “no power plant will be allowed to emit more than they do today — or as much as they did one or two years ago.” However, environmental advocates warn this stance still allows for increased mercury emissions. James Pew, director of federal clean air practice at Earthjustice, told ABC News, “These decisions allow more mercury into the air and water, even though mercury is known to harm children’s brain development, and arsenic is linked to cancer and birth defects.”
Further complicating the regulatory landscape, the U.S. Supreme Court struck down a Clean Water Act requirement in March that forced polluters to comply with water quality standards as a condition of their permits. Additionally, in May 2025, the House of Representatives narrowly voted 216 to 212 to let about 1,800 facilities—including chemical plants, refineries, and pesticide manufacturers—reclassify themselves as minor polluters. This move exempts them from controlling, monitoring, or reporting toxic emissions under the Congressional Review Act. The Senate had approved the resolution weeks earlier.
Patrick Drupp, Climate Policy Director at the Sierra Club, criticized these rollbacks, stating, “All of Donald Trump’s actions since taking office are taking us backwards on mercury pollution and threatening our health.” Dan Esty, a Yale University professor of environmental law and policy, highlighted mercury as one of the clearest examples of public health knowledge translated into environmental standards over the past 50 years, underscoring the risks posed by the current regulatory retreat.
Paul Anastas, director of the Center for Green Chemistry and Green Engineering at Yale and a former EPA assistant administrator, emphasized the gravity of mercury exposure. “It’s always foolish to ignore mercury,” he said. “...If you’re not afraid of mercury, you’re not paying attention.” Ryan Maher, an environmental health attorney for the Center for Biological Diversity, warned that the rollbacks could lead to more child deaths and increased cases of cancer, lung disease, and heart attacks.
Mercury contamination is already a pressing issue in parts of the United States. For example, Minnesota’s Pollution Control Agency advises residents to limit fish consumption from local rivers and lakes to once per week due to elevated mercury levels. Zhang noted that the eastern U.S., home to many industrial sites potentially releasing mercury, could face heightened impacts if regulatory protections weaken.
Beyond human health, the study also highlights ecological concerns. Rivers near critical wildlife habitats, including major bird migration flyways in East Asia and North America, have experienced sharp mercury increases, threatening biodiversity. The researchers suggest that riverine mercury concentrations could serve as a rapid-response metric to evaluate the effectiveness of pollution governance as countries strive to meet the goals of the Minamata Convention on Mercury, an international treaty aimed at reducing mercury emissions worldwide.
In sum, this groundbreaking research shines a stark light on how industrialization and human activities have transformed mercury pollution in rivers, with far-reaching consequences for ecosystems and communities. It also underscores the urgent need for robust environmental regulations to protect public health and preserve natural habitats from the silent but potent threat of mercury contamination.
