Scientists warn of mercury threat in ocean due to human activity

A new study has revealed that human activities and climate change are accelerating the release of mercury from the world's largest marine mercury reservoir – continental shelf sediments.

The study, recently published in the journal Nature Sustainability, was led by researchers from Peking University in collaboration with experts from the United States, the United Kingdom and the Netherlands.

Mercury is a highly toxic global pollutant that can accumulate in food webs and pose serious risks to human health. Ocean sediments have long been considered a permanent storage site for mercury. However, the continental shelf, which holds the largest amount of mercury in the ocean, is now facing a rapidly increasing risk of mercury release.

By developing high-resolution datasets and coupled process-based models, the team precisely quantified the mercury storage capacity of global continental shelves and uncovered frequent disturbances caused by bottom trawling and climate-related processes.

The study shows that continental shelves store nearly 1,300 tonnes of mercury each year, six times more than previous estimates by the United Nations Environment Programme.

"Continental shelves act like the 'kidneys' of the ocean, effectively filtering toxic mercury from the water and reducing threats to coastal fisheries and human health," said Wang Xuejun, a co-corresponding author of the study. "However, trawling and dredging activities are now acting like 'scalpels' that damage this vital function."

The research further quantified the direct impact of human activities. Bottom trawling and dredging disturb over 5,000 tonnes of mercury in sediments annually, four times the amount buried each year.

At the same time, climate change is worsening the situation. Rising temperatures enhance the release of mercury from sediments. Model simulations indicate that with global warming of 1.5 to 5 degrees Celsius, the natural release of mercury from sediments into the water could increase by 6 to 21 percent by the end of the century.

Warmer oceans may also accelerate the breakdown of organic matter in sediments, further promoting mercury release. This process could combine with more frequent extreme weather events, leading to even greater mercury release, according to the study.

"When trawlers plow the seabed, they may accelerate the release of historical mercury buried for decades or even centuries," said Liu Maodian, another co-corresponding author. "Once this 'legacy mercury' is reactivated, it could re-enter food webs and pose renewed risks."

"Protecting the continental shelf mercury sink is closely linked to the United Nations Sustainable Development Goals, serving as a shield for human health and a guardian of marine ecosystems," Liu added. "Only by integrating mercury management, fisheries policies and carbon neutrality goals can we safeguard this last line of defense."