The EPA does allow a certain level of manganese in drinking water. To consumers, the permitted 0.05 milligrams per liter might seem non-existent. And interestingly, this amount is mostly for "aesthetic" reasons, Sain noted. This contaminant level was set, reportedly "based on bitter metallic taste, black-brown particles in water, and undesirable black or brown color of fixtures and laundry." But, in actuality, there is not a bitter metallic taste for manganese at that level, Sain and Dietrich revealed in a peer-reviewed journal paper, "Assessing taste and visual perception of Mn (II) and Mn (IV)." Undergraduate researcher Ashley Griffin of Franklin, Tennessee also contributed to the article that appeared in the January 2014 issue of the Journal of the American Water Works Association.
Mineral content in drinking water "is acknowledged to be the major chemical factor affecting taste and likeability of drinking water when no off-flavors are present," Sain and Dietrich wrote. But the problems occur when a mineral such as manganese is not detected by the human senses. They estimated that 50 percent of the population taste threshold for manganese II, the simplest ionic manganese oxide, to be more than 1000 times the current EPA allowable level. As it is "visually undetectable in drinking water, even at concentrations much greater than those typically found in groundwaterit could lead to ingestion of water with high manganese II concentrations."
With their findings, Sain and her adviser wondered about doubled contamination water and air. They posed the question of what happens when one inhales a drinking water that is co
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