Up to 60 million people in Pakistan are at risk of the deadly chemical arsenic, according to a new analysis of the sources of water.
The study analyzed data from about 1,200 groundwater quality samples from all over the country.
The resulting risk map shows concentrations well above the World Health Organization (WHO) safety guidelines across the plain of the Indus.
The research has been published in the journal, Science Advances.
Arsenic is a semi-metallic element that is found throughout the world in varying concentrations. Human beings come in contact with it because it leaches into the groundwater from the rocks and sediments.
The WHO says that around 150 million people worldwide rely on groundwater contaminated with arsenic.
Long-term exposure can lead to a variety of chronic health conditions, including diseases of the skin, cancer of the lung and bladder, as well as cardiovascular issues.
The WHO has established a level of 10 micrograms per liter as the permissible concentration in drinking water. In Pakistan, the government says that the 50 micrograms per liter is acceptable.
This new study shows that 50 to 60 million people who live in the valley of the Indus, which runs through a large part of eastern Pakistan, are drinking water which, very probably, exceeds its government a safe level.
The scientists collected soil water samples, taken from the wells of water that goes down into the Earth, in the 1,200 sites throughout the country. The team then used statistical methods for the construction of a “risk map” and to estimate the size of the population exposed to the threat.
Lead author, Dr. Joel Podgorski of the Swiss Federal Institute of Aquatic Science and Technology, told the BBC that the results were “alarming”.
“This is the first time that we have been able to show the extent of the problem in Pakistan. Due to the geology and soil properties and on the basis of all the measures we have taken, basically, and all the plain of the Indus is in high risk of having high levels of arsenic in groundwater.”
The researchers say that a major cause of the problem is that the sediments containing arsenic are relatively young.
So if an aquifer has been developed since the end of the last ice age about 10,000 years ago, is more likely to have high levels of arsenic in the water that the older, deeper aquifers, where most of the chemical has leached away.
Scientists also believe that the irrigation of agriculture is making the situation worse. The study found a strong correlation between high soil PH levels, and concentrations of arsenic.
“There is massive irrigation in the Indus valley, it is a hot and dry climate,” said Dr. Podgorski.
“If you have a lot of water flooding of the surface that is going to percolate to the aquifer, which would be an easy way to carry any arsenic down to the groundwater.”
The number of people likely to be impacted in Pakistan, according to the study, more than 20 million people affected in China. Some researchers, who welcomed the study, have reservations about the magnitude of the impact.
For David Polya, professor of environmental chemistry of the University of Manchester, there is a “considerable amount of uncertainty in the new figures”.
“Even if the population at risk was only half that estimated, this would mean that estimates of the number of people around the world affected by such high arsenic danger to the groundwater would have to be substantially revised upwards,” he said.
“This reflects a trend of the last few decades, where the growing number of people that have been recognized to be exposed to high concentrations of arsenic in the drinking water.
“As detailed studies of this type carried out in other areas, there is no doubt that the number of persons known to be exposed to this poison through drinking water will increase even more.”
Other researchers in the field say that everything that the overall accuracy of the numbers, the study is bringing much more attention to a problem.
“This new study provides information on the causes and extent of arsenic contamination that will be useful for Pakistan, as well as for the wider water sector,” said Dr. Rick Johnston, WHO.
“It points to the need for a strong monitoring of the quality of the water and to avoid the presence of arsenic in the drinking water for the exploitation of arsenic-free resources, or to effectively remove arsenic from drinking water.”
The only way to get a definitive answer to the scale of the exhibition is to do more testing on the ground, says Dr. Podgorski, the lead author.
“Ultimately, what our map shows is that this whole area should really be tested,” he said.
“Some are good, some are not, you need to go through each step to verify that every well.”
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