Researchers have found sharp increases in mercury levels in ecologically sensitive areas, including bird flyways in East Asia and North America, as well as Amazonian regions affected by mining and deforestation.
By Chloe Baul, Courthouse News Service
A Tulane University-led study finds that mercury levels in the world’s rivers have more than doubled since the 1850s, with gold mining, industrial waste, and soil erosion driving a rise that could threaten ecosystems and public health.
A study published on Wednesday in Science Advances offers the first global baseline of mercury pollution in rivers, estimating that pre-industrial levels were around 390 metric tons per year, compared to roughly 1,000 metric tons today. The rise is primarily driven by wastewater, soil erosion, and industrial and mining activities.
“Human activities have disrupted the global mercury cycle in every aspect,” said Yanxu Zhang, the study’s lead author and associate professor at the Tulane School of Science and Engineering, in a press release. “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.”
Mercury is a potent neurotoxin that can accumulate in fish and move up the food chain, posing health risks to both humans and wildlife.
Researchers found sharp increases in river mercury levels near sensitive habitats, including migratory bird flyways in East Asia and North America. To simulate how mercury moves through river systems, the team used the MOSART-Hg model, which aligned with sediment core data. Since 1850, North and South America have driven 41% of the global rise, followed by Southeast Asia (22%) and South Asia (19%).
In South America, mercury pollution is primarily associated with artisanal gold mining and deforestation in the Amazon region.
“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 said.
In East Asia, industrial mercury emissions are the dominant source of river pollution. Rivers in China now contribute more than 70% of the region’s mercury load, and the mercury flux in the Yangtze River has more than doubled compared to pre-industrial levels.
However, not all trends were upward.
The Mediterranean region saw a decline in mercury levels, which researchers attributed to dam construction, including the Aswan High Dam on the Nile, which traps mercury-laden sediment.
Zhang said that as countries work to meet the goals of the Minamata Convention on Mercury — an international agreement aimed at reducing mercury pollution — river mercury levels could provide a fast and visible way to track progress.
“The establishment of a baseline for riverine mercury during the pre-industrial era can serve as a key reference point,” he said.
