National Academies study confirms cancer risk from arsenic in drinking water
New studies strengthen the evidence of a link between bladder and lung cancer and exposure to arsenic in drinking water, says a new report from the National Academies' National Research Council.
WASHINGTON, D.C., September 11, 2001 — New studies strengthen the evidence of a link between bladder and lung cancer and exposure to arsenic in drinking water, says a new report from the National Academies' National Research Council.
"Even very low concentrations of arsenic in drinking water appear to be associated with a higher incidence of cancer," said Robert Goyer, chair of the committee that wrote the report and professor emeritus of pathology, University of Western Ontario, now living in Chapel Hill, N.C. "We estimated the risk of developing cancer at various arsenic concentrations, and now it is up to the federal government to determine an acceptable level to allow in drinking-water supplies."
The report's findings are consistent with those of a 1999 Research Council report that found high risks of cancer at EPA's maximum allowable level for arsenic in drinking water, which at the time was 50 micrograms per liter, or parts per billion. The agency lowered its standard to 10 parts per billion in January, but in March put the new rule on hold and asked the Research Council to review research findings from the last two years on the health effects of arsenic. In particular, it asked for an evaluation of the cancer risk posed by daily consumption of water with arsenic levels of 3, 5, 10, and 20 parts per billion.
The committee found that men and women who daily consume water containing 3 parts per billion of arsenic have about a 1 in 1,000 increased risk of developing bladder or lung cancer during their lifetime. At 5 parts per billion, the risk is about 1.5 in 1,000; at 10 parts per billion, it is greater than 3 in 1,000; and at 20 parts per billion, it is close to 7 in 1,000.
The committee's risk estimates are greater than those on which EPA based its pending rule in January because the committee used some different estimation methods and assumptions. For example, it compared cancer rates between people exposed to arsenic in southwestern Taiwan and a large, mostly unexposed Taiwanese population, whereas EPA only compared cancer rates within the study population itself. EPA also assumed that the Taiwanese consumed more food and cooking water that contain arsenic than the committee considered reasonable.
The committee addressed only the hazards from consuming water contaminated with arsenic, which can seep from natural sources or be discharged by agricultural and industrial processes. It was not asked to evaluate current levels of arsenic in U.S. drinking water supplies or to make policy recommendations, nor was it asked to carry out any of the cost-benefit analyses the government will need in order to set a maximum allowable level for arsenic in drinking water.
At the time of the 1999 report, studies from southwestern Taiwan — where people were exposed to large amounts of arsenic in drinking water — were judged to provide the best data for estimating cancer risks. Since then, additional studies in Taiwan, Bangladesh, Chile, China, and Finland have shown an association between exposure to arsenic in drinking water and cancer. A study in Utah found no link between arsenic exposure and bladder and lung cancer, but the committee observed limitations in the study that preclude its use for making quantitative risk estimates.
The committee chose to estimate risks to the U.S. population using data in studies from southwestern Taiwan and northern Chile. It also pointed out that additional data from a well-designed study in northeastern Taiwan, as well as from older studies in Argentina and Chile, provide supporting evidence. EPA also used the southwestern Taiwanese studies in its own analyses.
It has been argued that poor nutrition might make the Taiwanese population more susceptible to the effects of arsenic than the U.S. population, but the committee found no evidence of nutritional factors accounting for the high rate of cancer observed there. The strong association between arsenic exposure and cancer also has been demonstrated in countries such as Chile and Argentina, where poor nutrition is not an issue.
The report bases its risk estimates on the background incidence of cancer in the United States, not Taiwan. Using the background rate of the country of interest - the United States in this case - is standard practice in epidemiological studies when cancer rates are being compared among different populations. However, some committee members believe there is insufficient justification to select the background rate of cancer in one country instead of the other in this instance, and that it is important to present the risk based on the Taiwanese background rate as well.
Because the background incidence of lung and bladder cancer is lower in Taiwan than in the United States, the projected risks to Americans are lower if based on the Taiwanese background rate. For example, at arsenic concentrations of 3 parts per billion in drinking water using the Taiwanese background rate, the lifetime chance of cancer for men and women in the United States is 4 in 10,000; at 5 parts per billion, it is about 6.5 in 10,000; at 10 parts per billion, it is greater than 1 in 1,000; and at 20 parts per billion, it is more than 2 in 1,000. These risk estimates also are higher than what was assumed by EPA in January.
Increases in cancer caused by arsenic-contaminated water would be difficult to detect statistically in U.S. population groups, the committee noted, because the excess risk of cancer from arsenic is only a small percentage of the lifetime risk of cancer from all causes. For example, an excess risk of 45 in 10,000 for bladder cancer in males would only represent 13 percent of the total risk for male bladder cancer in the United States from all causes.
The data showing a relationship between chronic exposure to arsenic in drinking water and cancer are abundant. However, more research is needed to study the extent to which exposure also causes diseases other than cancer, the committee said. Some studies overseas have linked arsenic exposure to diabetes, respiratory and cardiovascular ailments, and birth defects. Future studies also should be large enough to detect risks to potentially sensitive groups, such as children and smokers. In addition, the biological mechanisms by which arsenic causes cancer need to be better understood.
The committee's work was funded by the U.S. Environmental Protection Agency. The National Research Council is a private, nonprofit institution that provides science policy advice under a congressional charter granted to the National Academy of Sciences.
NOTE: The report Arsenic in Drinking Water: 2001 Update is available on the Internet at http://www.nap.edu. Copies are available for purchase from the National Academy Press later this fall; tel. (202) 334-3313 or 1-800-624-6242. Reporters may obtain a pre-publication copy from the Office of News and Public Information (contacts listed above).