Forty years ago, Bangladesh was facing a health crisis. Contamination of water sources throughout the country were causing an incredibly high rate of child mortality, with more than a quarter-million children dying each year from waterborne infectious diseases. As a solution, international charity organizations launched a massive humanitarian effort to bring cleaner water to the Bangladeshis, installing roughly 10 million hand-pumped wells that brought up water from deep underground.
It wasn’t until more than 20 years later that scientists discovered how that well-intentioned plan had backfired. Though the underground water was free from the bacterial contamination of surface sources, it was tainted instead with arsenic, the toxic chemical that can cause skin abrasions, cancer, and other diseases. A survey by the World Health Organization found that as many as 77 million people – half the population of Bangladesh – were drinking water with levels of arsenic higher than the recommended safe limit of 10 µg/L. Unflinchingly, the WHO characterized the situation as “the largest mass poisoning of a population in history.”
There’s no dispute that arsenic is bad for you, as indicated by its notorious and frequent role as a poison in mystery plots. But at lower, chronic doses, it has been hard to characterize just how dangerous arsenic can be to a person. Epidemiological studies of its toxicity have been able to retrospectively correlate increased rates of disease with the average amount of arsenic exposure in a particular area or group, but such studies lack specificity and can be distorted by various factors. In bleak fashion, the tragedy in Bangladesh offered a perfect setting for determining more precisely how decades of arsenic exposure can increase the risk of disease and death.
Such a study was launched in 2000 by Habibul Ahsan, director of the Center for Cancer Epidemiology and Prevention at the University of Chicago Medical Center. With a project called the Health Effects of Arsenic Longitudinal Study, or HEALS, Ahsan’s group laid out an ambitious plan to measure the arsenic levels in thousands of wells and people, who could then be followed to assess the health effects of their exposure. Beginning in late 2000, hundreds of staff members fanned out across Bangladesh, traveling by car, foot, or (during the rainy season) boat to remote villages where blood and urine samples were gathered and well water was sampled. After 18 months, nearly 12,000 subjects in a Bangladeshi region called Araihazar were recruited, nearly all of whom provided follow-up urine samples roughly every 2 years thereafter.
All that legwork gave the HEALS researchers a baseline from which to track the mortality of individuals with different levels of arsenic exposure. Over 9 years of monitoring (so far), more than 400 of their subjects died for various reasons. By indexing those deaths with whether the person’s urine samples showed high, moderate, or low level arsenic exposure and controlling for other factors such as age, sex, smoking and body mass, the researchers could make firmer conclusions about arsenic’s toll.
The results, published this weekend in The Lancet, were staggering. For the quarter of the subject pool drinking water with the highest levels of arsenic (an average of 27 times the safe level), the risk of dying from a chronic disease was nearly 70 percent higher compared to those below the safe level. Those drinking a more moderate dose of arsenic in their water – from just above the safe limit of 10 µg/L to 15 times the limit – also showed an increased risk of mortality of roughly 20-30 percent. The latter result is relevant to people around the world, including parts of the United States where arsenic levels in groundwater remain dangerously high.
An expansion of the HEALS project to 20,000 subjects, underway since 2007, will help answer questions about the effect of these moderate doses above the safe limit.
“With a larger population, we can make much more definitive conclusions on whether this low dose exposure between 10 and 150 micrograms that some US populations have been exposed to are indeed deleterious, increasing cancer or even deaths,” Ahsan said.
Even more distressing was the change in risk – or lack thereof – in individuals who were moved from a high-arsenic to low-arsenic water source over the course of the study. The mortality risk for those moved to a cleaner water source during the study was still elevated by 56 percent at the first follow-up, and 67 percent at the second. The lack of improvement suggests that the effect of high-level arsenic exposure over two decades is not easily undone.
“This says that further exposure to arsenic for those individuals already exposed needs to be reduced immediately, if possible,” Ahsan said. “Unfortunately, in a developing country such as Bangladesh, the real solution of replacing the source of drinking water from contaminated to safe water sources for 50 million people is quite a task.”
But Ahsan said that his group and others are not giving up on the people of Bangladesh. On one side, the HEALS researchers hope their data will convince the government and charity organizations to move more quickly in testing wells and finding clean water sources for those in contaminated areas, to help those who have only had limited or no exposure to arsenic to this point. Meanwhile, another ongoing research project by Ahsan and colleagues is studying the effectiveness of simple antioxidants – vitamin E and selenium – in blunting the toxic effect of arsenic exposure. The hope is that this time, good intentions will serve their purpose and improve the quality of life for Bangladeshis without unexpected consequences.