By Michael Kahn
LONDON, Aug 29 (Reuters) - Naturally-occurring arsenic in drinking water poses a growing global health risk as large numbers of people unknowingly consume unsafe levels of the chemical element, researchers said on Wednesday.
The problem is bigger than scientists had thought and affects nearly 140 million people in more than 70 countries, according to new research presented at the annual Royal Geographical Society meeting in London.
Arsenic can cause lung disease and cancers, even long after people stop drinking contaminated water, said Peter Ravenscroft, a researcher at the University of Cambridge.
"What is new is the extent of arsenic pollution is much bigger than people realised," Ravenscroft said in a telephone interview.
"There is a very important connection between arsenic in water and arsenic in food, especially where people grow irrigated corps."
World Health Organisation guidelines set a safe limit of 10 parts per billion of arsenic in water supplies but tens of millions of people in the world drink unsafe water above that level, researchers said.
At present, Bangladesh is the worst-affected country. There, hundreds of thousands or people are likely to die from arsenic poisoning, the researchers said.
Arsenic has also been found in the water in developed countries and industrial activities such as mining can also lead to contamination.
Rising awareness has led to increased testing that has revealed more widespread arsenic in drinking water but other researchers said even more must be done to address the problem.
"Most countries have some water sources with dangerous levels of arsenic, but only now are we beginning to recognise the magnitude of the problem," Allan Smith, a researcher at the University of California, Berkeley and adviser to the WHO on arsenic, said in a statement.