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Toxic metal mining waste could impact 23 million people

Model shows how 4 toxic metals have likely spread downstream from metal mines and waste storage facilities

by Katharine Bourzac, special to C&EN
September 29, 2023


A bright blue pool of water, surrounded by machinery, with mountains and dirt roads in the background.
Credit: Jose Luis Stephens/Shutterstock
Researchers modeled the spread of metals due to slow-moving processes that could expose millions of people to contaminated dust, sediment, and seepage.

Toxic contaminants from metal mining have infiltrated hundreds of thousands of kilometers of river channels around the world, exposing about 23 million people to potentially unsafe levels of lead, zinc, copper, and arsenic (Science 2023, DOI: 10.1126/science.adg6704).

“We’ve seen a lot of evidence about the way mining can affect river systems,” says University of Exeter mining researcher Karen Hudson-Edwards, one of the leaders of the study. They decided to model the problem on a global scale because, she says, “The message about chronic contamination of rivers is not getting out.”

When the tailings dams that hold mining waste fail, they can unleash huge amounts of contaminated water into the environment, and that gets a lot of attention, says Hudson-Edwards. She says her team’s modelling study highlights the risk caused by slower processes such as the spread of metal-contaminated dust and sediment, seepage from storage facilities, and other processes. The researchers found that 50 times more people are exposed to chronic contamination than are impacted by tailings dam failures.

To fill in this picture, the researchers gathered data about active and inactive metal mines and tailings dams around the world. They combined this with information about rivers and human and livestock populations downstream from these mines. Then they modelled the extent of the world’s rivers and lands that are likely contaminated with metal mining waste, drawing on decades of knowledge about how these materials move through the environment. They estimate that 23.48 million people are at risk of being exposed to potentially unsafe levels of copper, lead, zinc, and arsenic. People can be exposed to these metals in dusty air, drinking water, and food grown on contaminated land.

Richard Marcantonio, an environmental scientist and policy specialist at the University of Notre Dame, says the results are “very, very concerning.” And he adds that the model leaves a lot out. The study did not account for mercury, a common waste product of gold mining, or many of the metals released when mining for battery materials, such as cadmium, chromium, and cobalt. The study also can’t account for small-scale mining, which is often dirtier, and not recorded in databases. Hudson-Edwards says they were limited by available data, and that the team is expanding their model to be more comprehensive.

Climate change is likely exacerbating the spread of toxic metals. The world is getting windier, says Hudson-Edwards, which means it’s more important than ever to control dust at active mines, and to cover tailings storage facilities. Dry conditions caused by more frequent drought speed the formation of metal salts, which dissolve faster when it rains. And increased risk of flooding means more water to move these metals around, contaminating new places, but also potentially diluting toxic metals to safer levels, says Hudson-Edwards.

“Mining is vital now as we’re trying to move away from oil,” says Hudson-Edwards. There’s a big push to develop new mines to meet the growing demand for battery metals. Hudson-Edwards says she hopes highlighting the ongoing risk from historic mining will make governments and mining companies more mindful going forward. “It’s in everyone’s interest to make mining sustainable.”


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