MIAMI - Levels of arsenic in the groundwater of eastern Pakistan are "alarmingly high" and pose a significant health hazard to tens of millions of people who drink the water, researchers said Wednesday.
The study in the journal Science Advances is the first to create a comprehensive map of arsenic in the groundwater across Pakistan , and follows earlier, smaller studies that showed high arsenic levels in some places.
Areas in eastern Punjab - which includes Lahore - and around Hyderabad were especially likely to have groundwater that exposes large numbers of people to arsenic contamination.
Many parts of the densely populated plains along the Indus River and its tributaries showed arsenic concentrations in groundwater were higher than the World Health Organisation guideline of 10 micrograms per litre, said the report.
"Very high concentrations, above 200 micrograms/litre, are found mainly in the south," it warned.
Overall, 50 to 60 million people use groundwater which very likely contains more than 50 micrograms per litre, or five times higher than WHO guidelines.
"This is an alarmingly high number, which demonstrates the urgent need to test all drinking water wells in the Indus Plain," said lead author Joel Podgorski, a geophysicist at the Swiss Federal Institute of Aquatic Science and Technology (Eawag).
Rice, wheat, cotton and sugarcane are heavily farmed in the area.
Podgorski said more water from wells in high-risk areas must be tested, because concentrations of arsenic can vary widely in small areas.
Also, more testing is needed because local aquifer conditions cannot be predicted sufficiently accurately by modelling. If the suspected link to irrigation practices is confirmed, new techniques would need to replace current practices.
Pakistan is aware of the growing problem, with arsenic levels rising in some areas as people increasingly and indiscriminately draw from the country's underground aquifers, said Lubna Bukhari, who heads the government's Council for Research in Water Resources.
"It's a real concern," she said. "Because of lack of rules and regulations, people have exploited the groundwater brutally, and it is driving up arsenic levels."
The authors of the study developed a map highlighting areas of likely contamination based on water quality data from nearly 1,200 groundwater pumps tested from 2013 to 2015, and accounting for geological factors including surface slope and soil contents. They determined some 88 million people were living in high-risk areas.
Given that about 60-70 percent of the population relies on groundwater, they calculated that roughly 50 million — maybe even 60 million — were potentially affected. That's equal to at least a third of the 150 million already estimated by the World Health Organisation to be drinking, cooking and farming with arsenic-laced water worldwide.
South Asian countries concerned with pathogen-infused surface water have been pumping enormous volumes of groundwater, causing the water tables to drop drastically and tapping into new water pockets tainted by the colorless, odorless toxin.
"This study is important because it draws attention to an overlooked — yet solvable — problem of vast magnitude affecting the health of millions of villagers," said geochemist Alexander van Geen of Columbia University's Lamont-Doherty Earth Observatory, who was not involved in the study . He said the patterns it identifies are broadly consistent with data he and other researchers have collected from some 10,000 well tests in the region.
One of those researchers, Abida Farooqui, assistant professor of environmental sciences at Islamabad's Qaid-e-Azam University, said the new study 's sample size may be too small to draw clear conclusions.
"The study revealed very important and an emerging problem of arsenic in the country," Farooqui said. But "only 1,193 samples have been used to predict the situation in the whole Indus Valley, which is unrealistic."
In any case, no map can tell villagers whether a specific well is contaminated. Arsenic concentration varies widely from pump to pump, and the only way to know for certain is to test each one.
Shallow wells are less likely to be tainted. Deeper ones, such as those run by the government's Drinking Water Filtration sites, may be more at risk .
This makes the problem especially acute for thousands of city-dwellers who have no access to clean water and rely on what the government supplies. At one Islamabad neighbourhood filtration site on Wednesday, resident Ali Hasan said the struggle was real.
"It's the government's job to provide us with clean drinking water, but everywhere we have to travel to find clean water," Hasan said while filling a large plastic jug to take home to his neighbourhood.
A survey submitted to Pakistan 's parliament last year suggested nearly 80 percent of water sources in 2,807 villages across 24 districts were contaminated with bacteria or other pollutants, to levels that were unsafe to drink.
Now, "the presence of arsenic in drinking water is becoming a widespread health problem," said Luis Rodríguez-Lado, a chemist with the University of Santiago de Compostela in Spain who was not involved in the study . Yet "there is a general lack of information" about which areas in Asia are most at risk .