Thousands of massive dams built to store toxic mining waste are scattered across the world, raising growing concerns among scientists and environmental experts about the potentially catastrophic consequences if these structures fail. Known as tailings dams, these facilities hold billions of tonnes of mining byproducts—often containing dangerous chemicals and heavy metals—that can devastate ecosystems and communities if released.
A recent disaster in Zambia illustrates the scale of the risk. In February 2025, a tailings dam at the Sino-Metals Leach copper mine collapsed, unleashing more than 50 million cubic litres of acidic waste and heavy metals into the Chambishi stream, a tributary of the Kafue River. The toxic flood killed large numbers of fish and wildlife, contaminated farmland and disrupted drinking water supplies for the city of Kitwe, which has a population of about half a million people. Authorities described the incident as a major environmental emergency, with pollution detected many miles downstream.
Tailings dams are built to store the leftover slurry produced during the extraction of metals and minerals. This waste typically consists of mud, rock fragments and contaminated water containing substances such as arsenic, mercury and other heavy metals. These structures are often enormous—some among the largest engineered constructions on Earth—and are designed to contain waste indefinitely. However, experts warn that maintaining them safely over decades or centuries poses a huge challenge.
The consequences of a dam failure can be catastrophic. When a tailings dam bursts, a torrent of toxic sludge can rush downstream, destroying homes, contaminating rivers and causing loss of life. One of the most notorious incidents occurred in 2019 in Brumadinho, Brazil, where a dam collapse killed 272 people after a wave of mining waste engulfed nearby facilities and communities. Four years earlier, another dam failure in Mariana released vast quantities of pollution that spread along more than 400 miles of river systems and severely damaged aquatic ecosystems.
Scientists also warn that the environmental effects of such disasters can last for decades. Heavy metals in mining waste do not break down easily and can accumulate in soils, rivers and food chains. This contamination can inhibit plant growth, alter soil microbes and threaten wildlife populations long after the initial spill. In some cases, entire ecosystems are permanently altered.
Globally, the number of tailings dams is enormous, with estimates suggesting tens of thousands of such facilities exist worldwide. Yet the full scale of the problem remains poorly documented because the mining industry often lacks transparency about the location and condition of these sites. Researchers have identified dozens of dams located in areas of high biodiversity, raising fears that failures in such regions could cause irreversible ecological damage.
Climate change is further increasing the risk. More intense rainfall, flooding and extreme weather events are placing additional stress on ageing dams that were not designed to withstand such conditions. Experts warn that without stronger oversight, better engineering practices and long-term monitoring, the probability of future disasters could rise.
While mining companies have introduced safety standards and industry guidelines in recent years, critics argue that compliance remains inconsistent and enforcement is weak. Environmental scientists say the world is effectively leaving behind vast reservoirs of toxic waste that will require maintenance for generations.
As global demand for minerals—especially those used in renewable energy technologies—continues to grow, the challenge of safely managing mining waste is expected to intensify. Experts warn that unless governments and companies take stronger action, these tailings dams could remain one of the mining industry’s most dangerous and persistent environmental threats.
