Water quality

9.5.5 Heavy metals

Used in a range of industrial and agricultural sectors, heavy metals exhibit widespread environmental distribution. Heavy metals from industrial activities, and large-scale and artisanal mining, have seriously degraded water in some Asian, Pacific and South American countries (Da Rosa et al. 1997; Spitz and Trudinger 2008; Sikder et al. 2013; Annex 9-1). They can bioaccumulate in plants grown with contaminated irrigation water (Arunakumara, Walpola and Yoon 2013; Lu et al. 2015). Many (mercury, lead, chromium, cadmium) are toxic to humans and aquatic organisms (Kim et al. 2017).

Heavy metals associated with water-intensive mining are problematic in Africa and Latin America (Annex 9-1). Water drainage from active and abandoned mines can cause significant water degradation (e.g. mercury and arsenic used in gold mining can pollute surface and groundwater). Examples of untreated mine-water discharging into streams and rivers include Mount Morgan (Australia) and Tisza River (Hungary), where reservoirs, agricultural irrigation water and aquatic ecosystem biodiversity have all been degraded. Groundwater pollution also has been reported to have occurred in Alberta, Canada because of the tar sands industry (Timoney and Lee 2009).

Groundwater contamination with naturally occurring arsenic occurs in South Asia and other countries in Asia and the Pacific (Rahman, Ng and Naidu 2009; Annex 9-1). Arsenic mobilization can also be facilitated or worsened through such human activities as metal mining and groundwater abstraction and, in some cases, through use of arsenic-based pesticides in agriculture and wood preservation. Although some problems remain, heavy metal contamination has generally diminished in EU countries since 2000. A dramatic example of heavy metal contamination involved Flint, Michigan (United States of America). A decision to switch the city’s drinking water supply in 2014 from Lake Huron to the Flint River, containing more corrosive water, released lead from leaded pipes in the city’s water distribution system, with significant human health impacts (Masten et al. 2016).