Climate Change Is Acidifying and Contaminating Drinking Water
For years, scientists have known that climate change is acidifying the oceans. Absorbing human-produced carbon dioxide emissions changes saltwater's mineral balance and harms sea life. But recently, researchers have found that acidification also occurs in freshwater, the main source for our drinking water.
The process is different, however. For example, in lakes and reservoirs, excess carbon dioxide feeds vegetation, and rising temperatures extend the growing season. When plants die, carbon breaks down and gets washed into nearby waters. In Germany, researchers saw a significant increase in carbon dioxide and acidity in several reservoirs, according to an article published in Scientific American.
But other mechanisms are also at work. In Colorado, recent research indicates that climate change could acidify source waters and degrade drinking water supplies in dry mountain regions throughout the West.
Greater Acidity, Lower Water Quality
Researchers from the University of Colorado discovered that droughts in high alpine areas along the Snake River are increasing water acidity and leaching more minerals into watersheds. That's occurring in areas where abandoned mine workings drain—producing acid mine drainage (AMD)—as well as where no mines exist.
The water quality issues associated with mines are exacerbated by natural acid rock drainage (ARD) in high elevation headwaters. In both instances, drainage includes heavy metals such as lead, cadmium, and zinc. But today, greater quantities of rare earth elements are making their way into tributaries due to altered stream processes and natural weathering. Health impacts are unknown, and the U.S. Environmental Protection Agency (EPA) does not have standards for rare earth elements in drinking water testing or requirements for monitoring these elements.
That's of concern, given that 58% of streams that feed public drinking water systems are in headwaters, according to the EPA. Increased mineral content may require additional water testing and treatment but could also present an opportunity to recover the rare earth elements for use.
Heavy Metal and Rare Earth Soup
Federal estimates show more than 100,000 abandoned mines on public lands in the U.S.—many of them in the west—according to the Center for Western Priorities. Areas rich in minerals are frequently associated with rocks containing pyrite. When exposed to air and water, these rocks produce sulfuric acid. The water's pH—a measure of acidity—often determines the amount of dissolved heavy metals it contains.
Climate change means longer summers and less snowy winters. Stream flows that last longer but carry less water cause more leaching due to low pH. These flows also concentrate metals that more snowmelt might dilute. The combination results in rare earth elements at concentration orders of magnitude higher than surface waters usually contain.
Rare Earth Harvest
Rare earth elements like yttrium, terbium, erbium, cerium and lanthanum aren't included in toxicity or monitoring standards. These elements are typically used to produce many high-tech products including smartphones, hard drives, electric and hybrid vehicles, flatscreen monitors, and televisions. At present, the supply of rare earth elements comes mainly from China.
Traditional water treatment doesn't remove rare earth elements. In fact, some cities in Europe now label them as emerging contaminants to drinking water supplies, according to the European Environment Agency. Contamination is a concern in the case of the Snake River because it flows into the Dillon Reservoir, the major source of stored water for the city of Denver.
In the Environmental Science & Technology paper summarizing the research, authors Garrett P. Rue and Diane M. McKnight suggest recovering the rare earth elements from waters. Harvesting could result in a source of valuable materials and also help mitigate the impacts of increased acidity and mine drainage on drinking water sources. That solution will require investment in technology and infrastructure to produce the positive impacts desired.