In 2014, the World Health Organization estimated that approximately 200 million people across the globe are being exposed to dangerous levels of arsenic through their drinking water. Most of those affected, the report stated, live in southern Asian countries such as Bangladesh, Cambodia, India, Nepal and Vietnam. But as Kathy Gannon and Katy Daigle report for the Associated Press, a new study has revealed that arsenic-contaminated groundwater is also a rampant problem in another southern Asian country, Pakistan, where as many as 60 million people may be at risk.

As part of the study, which was published in the journal Science Advances, researchers tested water drawn from about 1,200 groundwater pumps located throughout the country. According to Giorgia Guglielmi of Science, nearly two-thirds of the samples exceeded 10 micrograms arsenic per liter of water, which is the safety limit recommended by the WHO. Guidelines in Pakistan allow a higher threshold of 50 micrograms per liter. But in large swaths of the Indus River Valley, the concentrations surpassed both limits, exceeding 200 micrograms per liter.

The team then used statistical modeling to determine environmental factors that would affect arsenic concentrations in different regions, Zamira Rahim explains in CNN.

Using this data, researchers created a “hazard map” charting the risk of arsenic contamination across Pakistan. The results were staggering: between 50 and 60 million people may be consuming arsenic-laced water, the team calculated. Most live within the Indus Valley.

Arsenic does not have a smell or taste, making it difficult for laypeople to detect. Long-term exposure can have dire health consequences—among them skin lesions, cancer, developmental defects, cardiovascular disease and diabetes.

This potentially toxic element occurs naturally in the Earth’s crust, and typically, it stays locked in the rocks and sediment. But as Gannon and Daigle note in the AP, people in Pakistan have been “increasingly and indiscriminately” drawing water from underground aquifers.

“[I]n the last few decades, 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,” they write.

There are other factors contributing to the problem in Pakistan. According to Guglielmi, the highest concentrations of arsenic occur in areas where soil PH is relatively high and clay is relatively young; through the decades, arsenic leaches from geological sediments that have been exposed to water. Joel Podgorski, the study's lead author, tells CNN’s Rahim that human and animal waste in local water sources can also make the problem worse because “it causes a different type of arsenic release."

According to David Polya, a professor of environmental chemistry at the University of Manchester, who was not involved in the study, the study is cause for alarm even if the scope of the problem is smaller than the researchers estimate. "Even if the population at risk was only half that estimated, it would mean that the estimates of the number of people around the world impacted by such high arsenic hazard groundwaters would need to be substantially upwardly revised,” Polya tells the BBC's Matt McGrath.

What should be done about the country’s arsenic-contaminated groundwater? The authors of the study say that “[f]irst and foremost,” drinking water across the Indus Valley should be tested. And it is important, they note, to test individual wells, due to the “inherent high degree of small-scale spatial variability of geogenic arsenic contamination.”

Testing wells can help officials determine safe depths for drilling into groundwater. And as Guglielmi points out in Science, the government can invest in treatments that remove arsenic from water sources.

“Ultimately,” the authors of the study caution, “any treatment options must be socially acceptable and tailored to the local groundwater composition.”