Residents of riverine and floodplain ecosystems are increasingly exposed to environmental and health hazards associated with metal mining, according to an international research team. The accumulation and release of toxic waste from such activity poses a threat to an estimated 23 million people worldwide.

The study published in Science is based on a new georeferenced global database of 185,000 metal mines, process-based modeling and empirical testing. The analysis addressed contamination from all known active and inactive metal mining sites, including tailings storage facilities, with a focus on potentially harmful contaminants such as lead, zinc, copper and arsenic. These metals are transported downstream from mining operations and deposited along river channels and floodplains for extended periods.

Metal mining contamination in river systems is determined to affect approximately 479,200 km of river channels and encompass 164,000 km² of floodplains on a global scale. About 23.48 million people reside on these affected floodplains, supporting 5.72 million livestock and encompassing more than 65,000 km² of irrigated land.

The downstream dispersal of toxic concentrations of metals poses human health threats through direct exposure via skin contact, accidental ingestion, inhalation of contaminated dust, and through consumption of contaminated water and food grown on polluted soils.

Researcher from the University of Lincoln (U.K.), Aberystwyth University (U.K.), University of Exeter (U.K.), Vrije Universiteit Amsterdam (Netherlands), Monash University Indonesia, University of the Free State (South Africa), Bangor University (U.K.), University of Queensland (Australia) and the Indian Ministry of Earth Sciences contributed to this study.