Some 137 million people across the globe unknowingly consume water with unsafe levels of arsenic, according to new research. The odorless, tasteless chemical occurs naturally in soil, but also reaches drinking water from agricultural and industrial sources and the vials of paperback-mystery villains. Arsenic can lead to lung, bladder, and skin cancer and is “the most dangerous contaminant of drinking water in terms of long-term health risks,” says researcher Allan Smith. He adds, “I don’t know of one government agency which has given this the priority it deserves.”