Arsenic has a long and glorious history in the annals of crime fiction, but for the people of Bangladesh, poisoning by arsenic is all too real. With 35 million people drinking arsenic-tainted water, the country is in the midst of what the World Health Organization is calling the “largest mass poisoning of a population in history.” Ironically, the problem has its source in an ostensible solution: For two decades, the government and various international aid groups worked to wean the nation’s poor off of pond water, often the breeding ground for lethal diseases, urging them instead to install wells. But it turns out that many of the underground aquifers from which the wells draw water are contaminated with arsenic, which is causing “the highest environmental cancer risk ever found,” according to Allan Smith, an arsenic expert at the University of California at Berkeley.