Poison control
Epidemiologist Habibul Ahsan finds arsenic-contaminated drinking water responsible for one-fifth of the deaths in parts of rural Bangladesh.
By Lydialyle Gibson
Photography by The Uncultured Project
Many Bangladeshis have no choice but to use arsenic-tainted water.
The idea seemed simple, even obvious: to provide rural Bangladeshis with clean, bacteria-free drinking water, government and aid organizations in the 1970s dug ten million hand-pumped wells. Unsanitary surface waters had led to outbreaks of waterborne diseases like hepatitis and typhoid fever; every year more than 250,000 children died. And so, led by UNICEF, an international coalition installed tube wells throughout Bangladesh and neighboring West Bengal, India. Villagers began drawing cool water straight from the ground.
Then 20 years later, when a swarm of patients showed up in West Bengal clinics with skin lesions related to arsenic exposure, scientists discovered that those wells were contaminated. (Geologists later identified natural sediments washing down from the Himalayas as the source.) “Unfortunately, it wasn’t tested at the time whether the groundwater had toxic elements,” says Chicago epidemiologist Habibul Ahsan. “And as a consequence, tens of millions of people have been drinking water that has a high level of arsenic.”
Ahsan directs Chicago’s Center for Cancer Epidemiology and Prevention and teaches medicine, health studies, human genetics, and in the Committee on Cancer Biology. In June he published a ten-year study in Lancet detailing arsenic exposure’s effect on individual mortality. The findings were devastating. Moderate arsenic intake raises the risk of dying from chronic disease by 20 to 30 percent. High levels of arsenic—the average among Ahsan’s Bangladeshi study participants was 27 times the recommended safe limit—raise the risk by nearly 70 percent.
No one really knows, Ahsan says, how long it takes for arsenic to begin compromising a patient’s health, but long-term exposure leads first to blackening of the hands and feet, nodular growths, and later open sores and gangrene. In time, cardiovascular and reproductive problems and cancers of the bladder, skin, lungs, and liver can also appear. In children it’s been linked to neurological disorders.
Ahsan estimates the number of people in Bangladesh who’ve been exposed to arsenic since the 1970s at 50 million. According to the World Health Organization, the figure could be as high as 77 million. A few years after the situation came to light in the 1990s, the WHO issued a report calling it the “largest mass poisoning of a population in history.” Says Ahsan: “This is an emergency.”
A Bangladesh native, Ahsan remembers the wells. “I used to see them when I was young,” he says. “Fortunately, I never drank from them.” Instead, he grew up in Bangladesh’s cities, drinking sanitary water. “But 90 percent of the population lives in rural areas. And that’s where the problem is happening.”
Ahsan launched his study in late 2000, along with colleagues at NYU and Columbia University, where he taught before coming to Chicago in 2006. Called HEALS (Health Effects of Arsenic Longitudinal Study), the project tested arsenic levels in thousands of wells across Bangladesh and followed 12,000 subjects in the country’s Araihazar region. Every two years, HEALS researchers measured arsenic concentration in subjects’ urine. They also began counting the dead. By February 2009, 407 of their subjects had died, more than 20 percent of them from chronic diseases attributable to arsenic.
Even more troubling, the disease risk persists after exposure ends. Some subjects began using cleaner water sources during the study—researchers told villagers where to find wells that tested lower for arsenic—but those changes “didn’t make any difference to their excess risk of mortality,” Ahsan says. The finding is alarming, he adds, but not surprising. “People in research studies from Argentina, Chile, Taiwan”—which experienced groundwater arsenic exposure in the 1950s and ’60s—“they’re still publishing now, documenting excess mortality from cancer and cardiovascular disease after exposure that ended 30 or 40 years ago.”
In Bangladesh the arsenic exposure continues. Most people have nowhere else to go to find water, and, according to Ahsan, some remote villagers did not even know until 2000 that their wells were contaminated. “Many of them learned for the first time from us. They had no idea until we went there and notified them of what we were trying to do.” Now most people know how much arsenic is in their water, but there remains a “large fraction” of Bangladeshis, he says, who have yet to test their wells. “So they’re still unknown. It could be millions of people.”
Meanwhile, Ahsan has widened the scope of his research. In 2007 the HEALS project expanded. The original study investigated only total mortality. To analyze specific diseases and their individual mortality rates, Ahsan increased the number of subjects from 12,000 to almost 30,000.
He is also testing whether dietary supplements or drugs might counteract arsenic’s poisonous effects. One study, now in its fourth year, provides Vitamin E and selenium to 7,000 patients who already have arsenic-related skin symptoms. “In the biological system,” Ahsan says, Vitamin E and selenium “work together as an antioxidant.” Arsenic leads to cancer by causing oxidative stress that damages DNA and tissues. “We want to see if we can prevent cancer.”
Folate, or folic acid, which helps clear arsenic from the body, may also ameliorate the health effects. In a smaller study, Ahsan is exploring whether folate can offer at least a short-term benefit, “for individuals who are still getting arsenic from the water, because it would help excrete the arsenic that’s already accumulated in the body.”
Another large research question remains, Ahsan says: “What is the safe level of arsenic?” The WHO recommends no more than ten micrograms per liter of water, but that threshold may be too high or too low. The answer matters not only for Bangladesh, but also for other countries where lesser amounts of arsenic are found in groundwater—including in private wells across the United States.
In Bangladesh, knowing what the arsenic threshold needs to be could help ease the burden of changing the country’s water system. “If the requirement is zero arsenic,” he says, “that’s a bigger task for the government than if we can set it a little higher.” He is organizing a much larger study, of perhaps 250,000 subjects, to understand the effects of low doses. Says Ahsan: “We are still trying to learn from this tragedy.”Return to top