People in Bangladesh were plagued by waterborne diseases until several groups came to their aid by drilling groundwater wells. Although cholera and other diseases diminished, other problems started within a few years. People complained of patchy skin, stomach pains, gangrene, and the incidence of cancer increased. What was happening? Arsenicosis. Here is an advanced case of arsenic poisoning, China. (Photo courtesy of USGS.)
Bangladesh and a number of other Asian countries have naturally occurring arsenic in their groundwater. A recent field study ("Scientists solve puzzle of arsenic-poisoning crisis in Asia") investigated why. Bacteria turns out to be a culprit. When robbed of oxygen, these bacteria "breathe" using rust, arsenic, and other chemicals. The process of using the arsenic converts the arsenic into a form that dissolves easily in water.
"Every day, more than 140 million people in southern Asia drink groundwater contaminated with arsenic. Thousands of people in Bangladesh, Cambodia, India, Myanmar and Vietnam die of cancer each year from chronic exposure to arsenic, according to the World Health Organization."