Low-dose exposure to arsenic in drinking water increases risk for skin lesions

Jun 14 2006

Mailman School of Public Health study provides evidence that a population exposed to well water with arsenic concentrations of as little as 50 ug/l is at risk for skin lesions.

Millions of persons around the world are exposed to low doses of arsenic through drinking water. However, up until now estimates of the health effects associated with low-dose exposure had been based on research from high-dose levels. In a study of more than 11,000 people in Bangladesh, research conducted by Columbia University's Mailman School of Public Health clearly provides evidence that a population exposed to well water with arsenic concentrations of as little as 50 ug/l is at risk for skin lesions. The report also concludes that older, male, and thinner participants were more likely to be affected by arsenic exposure.

The Mailman School team of researchers evaluated the relationship between arsenic exposure from drinking water and premalignant skin lesions over the course of three years. Participants were evaluated for arsenic exposure based on well-water arsenic concentration and usage. "Because of the wide range of arsenic exposure in the study population and the relatively large sample size, we were able to estimate and report dose-response relations even at the very low end of the arsenic exposure range. In particular, arsenic exposure seems to increase the risk of skin lesions at the low end of exposure in this population," said Habibul Ahsan, M.D., MMedSc, associate professor and director of the Center for Genetics in Epidemiology in the Department of Epidemiology at the Mailman School of Public Health and principal investigator.

The researchers indicate that a unique opportunity exists in Bangladesh to study chronic arsenic exposure measured at the individual level, because the majority of the population uses a single well as their primary source of drinking water, while, for example, in the United States, people usually drink water from multiple sources. However, up until now even assessments at the individual level were extremely difficult because exposures measurements were from years past or the Bangladeshi population drank water from multiple sources.

Another obvious difference between the rural population of Bangladesh and other studied populations is that this population consumes a large amount of water, as much as 2.5-3 liters per day on average vs. 1 liter in the United States. Moreover, almost 100 percent of the drinking water for this population comes from one or two wells with relatively stable concentrations of arsenic.

The team of researchers note that skin lesions were less of a factor in the study for females in the study, and this may be due to the tendency of women in rural Bangladesh tend to cover their bodies more extensively than men. "It also is possible that hormonal and other biologic differences between men and women also could be responsible for part of the gender differences in the skin lesion risks," observed Joseph Graziano, Ph.D., Mailman School associate dean for research, professor of Pharmacology & Public Health, and professor of Environmental Health Sciences.

The study also found some evidence that participants with a higher body mass index were at lower risk of skin lesions than participants with a lower body mass index. "Lower body mass index reflects poorer nutritional status in rural Bangladesh, which could directly or indirectly influence the effect of arsenic. In particular, poor nutritional status may be associated with lower intake of the antioxidants, folates, and/or dietary proteins necessary for metabolism and detoxification of arsenic in the body, said Dr. Ahsan." The influence by gender, age and body mass should be considered in future research and policy decisions."

Skin cancer is the most common arsenic-related cancer. Nearly 100 million people in the world are chronically exposed to arsenic and, therefore, are at increased risk of skin and other arsenic-induced cancers.

The most common route of human exposure to arsenic is through ingesting drinking water that is naturally enriched with arsenic. With an estimated 57 million people in Bangladesh having been exposed to high levels of arsenic from drinking water, starting in the 1970s, UNICEF and the Bangladeshi government installed a large number of hand-pumped tube-wells to provide pathogen-free drinking water to the population of Bangladesh.

The study builds on some of the activities developed in coordination with the NIEHS-funded Superfund Basic Research Program, led by Dr. Joseph Graziano, whose primary goal is to elucidate the health effects and geochemistry of arsenic. The work of the Superfund involves studies at four sites in the U.S., and also focuses on carcinogenic, reproductive and childhood effects of arsenic exposure in drinking water in Bangladesh.