Arsenic-contaminated groundwater near the Indus River in Pakistan poses a significant health hazard to as many as 60 million people who rely on it for drinking water and irrigation, according to a new study in the August 23 issue of Science Advances.
Women collect water samples from a dug well in the Gujrat district of Punjab province. | Tasawar Khanam/ COMSATS
"The fact that this natural contamination of arsenic occurs in the densely-populated Indus Valley means that an astonishingly large number of people are potentially affected," said first author Joel Podgorski, a geophysicist at the Swiss Federal Institute of Aquatic Science and Technology .
World Health Organization guidelines say up to 10 micrograms of arsenic per liter of water is safe. The scientists found very high arsenic concentrations in plains along the Indus River with concentrations above 200 micrograms per liter mainly in the south, including near Hyderabad. Concentrations around 500 micrograms per liter were measured near the cities of Lahore and Mazaffargarh, as well as multiple areas scattered around Sindh Province in the southeast portion of the country.
Though arsenic contamination is deemed a health risk of global proportions by the World Health Organization, the magnitude of that risk is poorly known in many parts of the world.
"I am alarmed at how widespread high arsenic concentrations are in Pakistan," said Podgorski. "The full extent of the problem was not known until now."
Regular consumption of water that contains large amounts of inorganic arsenic, a colorless and odorless element leached from rocks and sediments, leads to a range of harmful health effects.
Since the arsenic concentrations found in Indus Valley groundwater are quite high, long-term consumption may result not only in skin discoloration but also in heart disease or skin, lung, bladder or kidney cancers, Podgorski said.
Podgorski and his colleagues created the first comprehensive "hazard map" of the poisonous element in Pakistan. They studied groundwater samples from nearly 1,200 sites throughout the country, collected mainly from hand and motor pumps.
The scientists then assessed environmental factors that may be related to arsenic movement and the size of the human population exposed to arsenic. They pinpointed potential risk areas and identified regions where groundwater is likely safe, said coauthor Michael Berg, head of the Department of Water Resources and Drinking Water at the Swiss aquatic institute.
"The maps that we have produced highlight the large-scale nature of the problem in Pakistan and indicate where to focus water testing efforts," Podgorski said.
They also found evidence that suggests irrigation could be making the problem worse, allowing arsenic to leach into groundwater.
Arsenic concentrations measured in groundwater across Pakistan. | Podgorski et al., Sci. Adv. 2017;3: e1700935
"In the hot, arid climate of the Indus Plain, widespread irrigation leads to a large amount of evaporation, which in turn increases the pH of the soil," Podgorski noted. "This higher pH is then associated with increased solubility of arsenic in water."
If the suspected link between irrigation and contamination is confirmed, irrigation techniques that result in less evaporation could prevent more arsenic from leaching into groundwater. Drip irrigation, for instance, that supplies water and nutrients directly to the plant roots offers one such alternative.
The scientists said the alarmingly high number of people at risk for consuming toxic levels of arsenic in Pakistan — over one-fourth of the population — warrants an urgent response.
The first step is to test the water in existing wells, Podgorski said, adding that safe and unsafe wells can be in close proximity.
"Once it is known which wells are contaminated, these can either be avoided as a source of drinking water or filters can be utilized to remove the arsenic," he said.
The Swiss institute team is also working on arsenic contamination prediction models for India and South America, which include regions where high levels of arsenic naturally occur in groundwater, according to WHO.