This is the first population-based study to clearly demonstrate significant impairment of lung function, in some cases extensive lung damage, associated with low to moderate arsenic exposure.
"Restrictive lung defects, such as we saw in those exposed to well-water arsenic, are usually progressive and irreversible," said the study's senior author, Habibul Ahsan, MD, MMedSc, Director of the Center for Cancer Epidemiology and Prevention at the University of Chicago Medicine. "They can lead over time to serious lung disease."
The study, conducted in Bangladesh and published early online in the American Journal of Respiratory and Critical Care Medicine, adds to a growing list of arsenic-related health problems that includes skin, bladder and lung cancers, cardiovascular disease, cognitive deficits and premature death. An estimated 77 million people—nearly half of the residents of Bangladesh, the world's eighth most populous country—live in areas where groundwater wells contain harmful amounts of arsenic.
Less is known about exposure to elevated arsenic levels from well water or foods in other parts of the world, including regions in Mexico and the United States. Researchers have recently begun to re-examine foods, such as rice syrup and apple juice, that contain more arsenic than the 10 parts per billion that is allowed in U.S. drinking water.
"It is challenging to conduct rigorous biomedical research in a place like Bangladesh that lacks the infrastructure for such projects," Ahsan said, "but over the last 12 to15 years we have learned how to meet those challenges. We now have a large series of related findings that map out exposures and illustrate the severity of the problem."
"Our findings reinforce the growing interest in looking more carefully at arsenic-exposure issues in the United States," he added.
The study, coordinated by Ahsan and co-author Faruque Parvez, DrPH, of Columbia University, was the next step in the Health Effects of Arsenic Longitudinal Study (HEALS), a long-term Bangladesh-based project, begun in 2000 and expanded in 2006.
A nation of major rivers and low-lying plains, Bangladesh is prone to frequent floods, which, along with sanitation shortcomings, have historically contaminated the nation's drinking water. This led to high rates of infectious disease and child mortality. In the 1960s, more than 250,000 Bangladeshi children died each year from waterborne diseases.
To protect those children, international charity organizations launched a massive humanitarian effort to provide clean drinking water. They installed roughly 10 million hand-pumped wells to bring up water from deep underground.
Nearly 20 years later, by the early 1990s, scientists realized that this well-intentioned plan had gone astray. Though the underground water was free from the bacterial contamination of surface sources, it was tainted with inorganic arsenic, a toxic element. This was "the largest mass poisoning of a population in history," according to the World Health Organization.
The HEALS team follows about 20,000 people in Araihazar, a region of central Bangladesh, about 20 miles east of the capital, Dhaka, with a wide range of arsenic levels in drinking-water wells. Between 2005 and 2010, the researchers evaluated 950 individuals who reported respiratory symptoms such as cough and shortness of breath to HEALS clinic doctors. The researchers tested each patient's lung function and documented his or her arsenic levels.
They divided the patients into three groups according to arsenic exposure, using two related measures: how much arsenic was in their drinking water and how much was in their urine.
Then, local physicians trained by pulmonologist Christopher Olopade, MD, of the University of Chicago, rigorously measured each patient's lung function using a spirometer with a focus on two standard lung-function tests: forced expiratory flow (FEV1, the amount of air a person can expel in one second) and forced vital capacity (FVC, the total volume of air exhaled after fully filling the lungs).
Both measures showed that arsenic's effects were dose-dependent. After they corrected for possible confounders, the researchers found that:
One-third of the participants had been exposed to the lowest arsenic levels, less than 19 parts per billion in water. They had no detectable arsenic-related loss of lung function.
One-third had been exposed to drinking water with a relatively low arsenic dose, 19 to 97 parts per billion. Their lung function, as measured by FEV1 and FVC, decreased slightly but was not significantly different from the group with the lowest arsenic level in water.
One-third were exposed to a moderate dose, more than 97 parts per billion. For this group, both spirometric variables were significantly decreased. Their FEV1 decreased by about three times as much as those exposed to 19 to 97 parts per billion and their FVC fell by about six times as much.
Smoking amplified the damage. About 90 percent of the men tested smoked.
"These results clearly demonstrate significant impairment of lung function associated with lower concentrations than previously reported," Ahsan said. "Those most affected were older, thinner, less educated and more likely to use tobacco. Many of these people have limited excess lung capacity. It made a significant difference in their lives."
"This suggests that a large proportion of the country's population are at increased risk of developing serious respiratory disease, including COPD, bronchitis and interstitial lung disease in the future," the authors conclude.
"This is not just a problem for South Asia," Ahsan said. "About 13 million people in the United States get water from a private well that contains more arsenic than the legal limit. And we are becoming more and more aware that exposure through certain foods might be a bigger issue than drinking water. No comparable, large, prospective study has been done in this country."
The National Institutes of Health funded this study. Additional authors include Maria Argos from the University of Chicago; Mahbub Yunus, Rabiul Hasan, Alauddin Ahmed and Tariqul Islam from the University of Chicago and the Columbia University Arsenic Project Office in Dhaka; Vesna Slavkovich and Joseph H. Graziano from Columbia University; Yu Chen and Stephanie Segers from New York University; and Mahmud Akter from the National Asthma Center, Dhaka.
John Easton | EurekAlert!
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