New research contradicts previous findings that arsenic contamination — an environmental crisis that affects more than 60 million people in the Bengal Basin — in groundwater may result from arsenic coming from man-made ponds, suggesting instead that it originates in sediments in aquifers.
Groundwater sites across southern and eastern Asia contains arsenic levels that can cause chronic poisoning, leading to skin lesions, respiratory and cardiovascular disease, and a range of cancers.
"Almost all the major rivers draining the Himalayas are affected," Scott Fendorf, a biogeochemist at Stanford University, United States, told Nature.
The crisis is particularly serious in in the Ganges delta of Bangladesh, where aid agencies encouraged the drilling of hand-pumped wells in the 1970s to avoid using surface water contaminated microbial diseases such as cholera. At the time, geologists did not know that groundwater was contaminated with arsenic.
And they still do not know how the arsenic gets into the groundwater. Man-made ponds could be seeping arsenic into the aquifers. But they may also be flushing out arsenic from aquifers and reducing contamination produced by sediments within the aquifers.
The scientific dispute — in press in Geophsyical Research Letters and led by Saugata Datta, a geologist at Kansas State University, United States — shows that government and funding agencies need to support studies at multiple sites, from the Himalayas to the Bay of Bengal, according to Abhijit Mukherjee, a hydrologist at the Indian Institute of Technology in Kharagpur, who is working with West Bengal's government to find ways of predicting where safe wells might be dug.
"If that is done we have a systematic way of comparing data from sites," he told Nature.
The main goal should be to learn how arsenic is getting into the groundwater, so that researchers can make wells safe, ensuring that such conditions are avoided, he added.