A study conducted by UK scientists reveals that at least 23 million people worldwide are living in areas prone to flooding, which are contaminated with potentially harmful levels of toxic waste resulting from metal-mining activities.

As the BBC reports, the researchers mapped both active and abandoned metal mines, totaling 22,609 active and 159,735 abandoned sites, to determine the extent of pollution caused by these mining operations.

Chemicals originating from mining activities can seep into the soil and water, posing risks to both the environment and human health.

The researchers emphasize the need for careful planning when establishing new mining operations, especially as the demand for metals essential for battery technology and electrification, such as lithium and copper, continues to rise.

Professor Mark Macklin from the University of Lincoln, who led the research, expressed concern over the ongoing impact of pollution from abandoned mines, stating, "What's alarming for me is the legacy - [pollution from abandoned mines] is still affecting millions of people".

The study, published in the journal Science, expands on the team's previous research regarding the movement and accumulation of pollution from mining activities in the environment.

To compile their data, the scientists gathered information on mining activity worldwide from various sources, including governments, mining companies, and organizations like the US Geological Survey. This data included the location of each mine, the type of metal extracted, and whether the mine was active or abandoned.

The majority of metals from metal mining become bound in sediment in the ground, which can be eroded from mine waste tips or contaminated soil and end up in river channels or flood-plains. The researchers utilized previously published field and laboratory analyses to estimate the movement of metal-contaminated sediment in river systems.

With this data, the scientists developed a computer model to calculate the extent of river channels and flood-plains globally that are contaminated by mining waste, both from current and historical mining activities.

The study revealed that approximately 23 million people worldwide live in areas considered 'contaminated.' However, it is challenging to determine the extent to which these individuals may be exposed to contamination. Nonetheless, agriculture and irrigation in these regions pose potential risks, as crops grown in contaminated soil or irrigated by polluted water can accumulate high levels of metals.

Animals grazing on flood-plains may also ingest contaminated plant material and sediment, especially following flooding events when fresh metal-rich sediment is deposited.

The researchers warn that with climate change and more frequent floods, the legacy of pollution from mining is likely to expand and persist.

Professor Jamie Woodward from the University of Manchester, who was not involved in the study, emphasized the need to address "silent pollution" stored in flood-plains. Monitoring efforts should focus on understanding how contaminants are transported and stored in the environment to assess hazards and implement mitigation measures.

The study underscores that metal mining has a long history as "humankind's earliest and most persistent form of environmental contamination," dating back to as early as 7,000 years ago when waste from mining began to contaminate river systems.