Researchers say tens of millions of people in Bangladesh have been exposed to toxic levels of arsenic from drinking contaminated groundwater.
The World Health Organisation has called the exposure the largest mass poisoning in history.
The researchers, from the University of Chicago medical centre, say more than 20% of deaths in a 10-year study of 12,000 people were caused by arsenic exposure from contaminated drinking water.
They estimate as many as 77 million people - half the population of Bangladesh - have been exposed to toxic levels of arsenic, a naturally-occurring element, since the installation of hand-pumped wells to tap groundwater in the 1970s.
