If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.



Global Arsenic Crisis

Models for predicting toxic hot spots improve, but more direct monitoring is needed

by Britt E. Erickson
September 23, 2013 | A version of this story appeared in Volume 91, Issue 38

Credit: Dipankar Chakraborti
A child drinks water found to contain 50 ppb arsenic inside a temple in Kolkata, India.
This is a photo of a woman and child get drinking water from a tube well inside a temple in Kolkata, India.
Credit: Dipankar Chakraborti
A child drinks water found to contain 50 ppb arsenic inside a temple in Kolkata, India.

Efforts to provide clean drinking water to millions of the world’s poorest people have become the worst mass poisoning of a population in history. Roughly 140 million people worldwide are now drinking from shallow wells dug to bypass bacteria-infested surface water. But these wells currently contain so much naturally occurring arsenic that consumers develop skin lesions and various forms of cancer.

The true extent of the arsenic problem, however, is unknown because wells in many parts of the world have yet to be tested for contamination. Also, it takes years for symptoms of arsenic poisoning to occur, and the severity of effects can change with age, nutritional status, and overall health. In addition, arsenic concentrations in ground­water vary over time, so wells that appear safe one year may be poisoned the next.

In areas where arsenic contamination has been identified, including parts of India, Bangladesh, and many countries in Southeast Asia, efforts to provide clean water have run into social and technical obstacles. It is often hard for people in these areas to travel to safer wells. And although some deeper wells have been drilled to avoid arsenic-rich sediments, even those wells are now becoming contaminated.

Rather than test every well in the world for arsenic contamination, which would take decades and cost millions of dollars, scientists are trying to use data that have already been collected to develop models to predict regions of the world that are likely to be arsenic hot spots. Efforts could then be focused on monitoring wells in those areas that are most prone to arsenic contamination.

Some scientists contend, however, that constantly fluctuating groundwater conditions mean no model will be predictive enough. The only sure way to find arsenic contamination is to go out and measure for it, says Dipankar Chakraborti, director of the Arsenic Research Unit at Jadavpur University, in Kolkata, India.

One predictive model for China was published last month in Science (DOI: 10.1126/science.1237484). It relies on parameters such as soil texture, wetness, and salinity. It also relies on good monitoring data and a strong understanding of the geochemical processes that lead to the mobilization of arsenic in groundwater.

The researchers used data from a massive effort to test individual wells throughout China for arsenic contamination under­taken by the Chinese Ministry of Health from 2001 to 2005. About 445,000 wells were tested in more than 20,000 villages, representing about 12% of the counties in China. Approximately 5% of the wells contained arsenic levels greater than 50 ppb, and 13% had levels greater than 10 ppb, the limit recommended by the World Health Organization.

By combining geospatial information and population data with the arsenic monitoring data, the researchers predicted that nearly 20 million people in China are living in high-risk areas. “Our model shows that high arsenic risk occurs mainly in northern China,” says Luis Rodríguez-Lado, a soil chemist at the University of Santiago de Compostela, in Spain, and lead author of the study.

High-risk areas are strongly associated with environments where oxygen levels in aquifers are depleted and in arid regions, Rodríguez-Lado says. On the other hand, arsenic concentrations in water from more highly oxygenated aquifers were less than 10 ppb, he notes.

Under anoxic conditions, organic carbon drives chemical reactions in which iron minerals that contain arsenic are dissolved. The arsenic is released into groundwater along with free iron. Arsenic can also be released under oxic conditions, but the pH has to be high enough to promote the release of arsenic from mineral oxides.

The China risk model was made possible through a collaboration between the Swiss Federal Institute of Aquatic Science & Technology (Eawag), where Rodríguez-Lado developed the model, and China Medical University (CMU), in Shenyang. “I think our paper will cause the Chinese government to pay much attention,” says coauthor Guifan Sun, a professor and medical doctor at CMU. As a next step, “we will give advice to the Chinese government to confirm areas predicted to be high risk, especially where population density is high,” he notes.

The researchers acknowledge that their model is not a substitute for screening wells. But they point out that it can save money and time by helping prioritize future monitoring efforts. “It is easy to implement, and it provides a quick overview of the areas potentially at risk,” Rodríguez-Lado says. Although the model was developed specifically for China, it can also be applied to other parts of the world, including arid regions of the U.S. Southwest, Rodríguez-Lado says.

But some scientists are skeptical that such a model could be used on a global scale because the mechanisms controlling the release of arsenic into groundwater can vary from one location to the next, and they are not completely understood.

Credit: Guifan Sun/CMU
Chronic exposure to arsenic can cause lesions of the skin, such as those shown here on feet.
This is a photo showing hyperkeratosis, a thickening of the skin’s outer layer of the feet caused by arsenic poisoning.
Credit: Guifan Sun/CMU
Chronic exposure to arsenic can cause lesions of the skin, such as those shown here on feet.

The model does not take into account factors such as irrigation pumping, which has been shown to play a role in arsenic mobilization, says Chakraborti. It also does not account for arsenic levels in wells changing over time, he says.

Chakraborti, an analytical chemist and former director of Jadavpur University’s School of Environmental Studies (SOES), has spent the past 25 years analyzing arsenic in well water in West Bengal, India, and surrounding areas. Chakraborti has seen arsenic levels in some wells increase from less than 10 ppb to 100 ppb. He has also observed areas in which one well is contaminated with arsenic, but another one only a meter away is not. The underground geology and hydrology are complex and vary from place to place, he says.

Human activities such as overpumping groundwater are also changing the way aquifer systems flow, making it even more difficult to predict arsenic contamination. Earlier this month, Alexander van Geen, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory, and colleagues showed that massive pumping of groundwater from a safe aquifer near Hanoi, Vietnam, is slowly sucking in water from a contaminated one (Nature 2013, DOI: 10.1038/nature12444).

Overpumping changes the groundwater flow and redox state of the aquifer sands, accelerating the intrusion of arsenic from the contaminated aquifer into the uncontaminated one.

The study suggests that deep wells, which have been drilled throughout India, Bangladesh, and Vietnam to reach water that is not in contact with shallow arsenic-rich sediments, are at risk of becoming contaminated with arsenic because of soaring water usage.

Similar processes may be occurring in other megacities where increasing demand for irrigation and municipal water is leaving aquifers dry, the researchers note. “We are altering systems all over the world,” says Michael Berg, a senior scientist and aquatic chemist at Eawag, and coauthor on both the Science and Nature papers.

Chakraborti thinks better data may improve the models, but they won’t substitute for actual testing. His lab has analyzed more than 400,000 well-water and biological samples from arsenic-affected villages in India. The group conducted the analyses for schools, nongovernmental organizations, and hospitals at little to no cost to the client. The lab has operated since 1994 as a self-funded unit, with no government money or outside donations.

What made that possible is Chakraborti’s passion to help people suffering from arsenic poisoning and his contribution of some of his own earnings to a research fund he set up jointly with the university. For nearly two decades, he donated all award money, consulting fees, and payments that he earned from analytical analyses to the research fund. Interest earned on the fund has been used to support studies conducted by SOES. The fund is now valued at about $190,000.

“Never has so much research of practical significance been accomplished with so little funding,” says Jerald L. Schnoor, an environmental engineer at the University of Iowa and editor-in-chief of Environmental Science & Technology. Chakraborti’s work has likely saved many lives already and prevented thousands of cases of arsenic poisoning, Schnoor notes.

The Indian government has spent some $800 million to survey wells and provide alternative water sources such as water from deeper wells in West Bengal alone, but it has spent little money to raise awareness about the problem or to help arsenic-affected families, Chakraborti tells C&EN. In developing countries, community-oriented research is most desirable, he says.

Many of the people in Chakraborti’s research group are also arsenic patients. Currently, they are in much better health than when they first joined the group, Chakraborti says, because they are no longer drinking the contaminated water and are eating more fruits and vegetables. They bicycle into villages to raise awareness of the dangers of arsenic in drinking water and collect water samples. Interest from the research fund pays their monthly salaries.

Even after 25 years of monitoring groundwater in arsenic-endemic districts of India, Chakraborti believes he has seen only a small fraction of the problem. “In 1988, when I started my work on arsenic in hand tube wells in West Bengal, I knew of only 22 arsenic-affected villages from three blocks in three districts of West Bengal. Now, in 2013, we know of 111 arsenic-affected blocks from nine out of 19 districts of West Bengal,” he says.

“The more we are surveying, the more and more arsenic-affected areas we are finding,” Chakraborti says. Without the monitoring, “we would not know the real magnitude of the calamity,” he points out.

Chakraborti’s work has inspired other researchers to pursue arsenic mitigation. Chakraborti “steadfastly brought the magnitude and severity of the arsenic crisis in the Indian subcontinent to the fore,” says Arup K. Sengupta, an engineering professor at Lehigh University who has won several awards for developing technologies to remove arsenic from water. “In the absence of his ground-level work, we could not deliver mitigation technology as we can today.”

Dozens of arsenic removal systems that rely on a reusable, polymer-based arsenic-selective adsorbent developed by Sengupta’s team are currently in use in various countries, including India, Nepal, Cambodia, and Argentina.

Despite efforts by Chakraborti, Sengupta, and many other scientists to survey and remove arsenic in groundwater, millions of people around the world are still drinking contaminated water. In India, safe water is often far away from a person’s home, and in summer and winter people do not want to travel because it is too hot or too cold, Chakraborti says. And some people, he adds, believe their skin problem is related to a sin they committed in the last birth or is a curse of the devil, so they continue to drink contaminated water. These are not problems that models or measurements can solve.


This article has been sent to the following recipient:

Chemistry matters. Join us to get the news you need.