(Beyond Pesticides, April 1, 2010)
While most previous literature on melanoma has focused on host factors and sun exposure, new research shows a link between several pesticides and this deadly form of skin cancer. Epidemiologists from University of Iowa, the National Institute of Environmental Health Sciences and National Cancer Institute found that agricultural workers who apply certain pesticides to farm fields are twice as likely to contract melanoma, providing support for the hypotheses that agricultural chemicals may be another important source of skin cancer risk.
Source: LA Times
The study, “Pesticide use and cutaneous melanoma in pesticide applicators in the Agricultural Heath Study” was published last month in the journal Environmental Health Perspectives. It examines cancer rates in 56,285 pesticide applicators in Iowa and North Carolina as part of the federal government’s Agricultural Health Study, a large, long-term study of pesticide applicators and their spouses.
Researchers asked the pesticide applicators how often they were exposed to 50 pesticides and compared their cancer rates. Each person’s exposure was then approximated by adding up the total days that the workers had been exposed and using information from survey results on how the chemicals were applied and what protective equipment was being used.
The pesticides that are identified by researchers in the study include four that are registered for use by the U.S. Environmental Protection Agencey (EPA): maneb, mancozeb, methyl parathion, and carbaryl; and two that have been voluntarily canceled by their manufacturers: benomyl and ethyl-parathion.
The researchers found that those who were exposed to these certain pesticides had a higher risk of cutaneous melanoma than workers who handled other pesticides. Though melanoma is infrequent among the workers that were studied – of the 56,285 people studied, 271 developed melanoma – researchers found that it increased in frequency among those with the highest exposure to several of the pesticides. Risks of the disease increased 2.5 times for applicators that were exposed to maneb or mancozeb for more than 63 days in their lifetime. Likewise, applicators who are exposed carbaryl for more than 56 days were 1.7 times more likely, while exposure to either methyl or ethyl parathion for more than 56 days increases their melanoma risks by 2.4 times.
Vice president of epidemiology and surveillance research at the American Cancer Society, and one of the researchers for a 2006 study linking pesticide exposure to Parkinson’s Disease, Michael Thun, M.D., M.S., remarked that this study is “better equipped than most to tease out data” because it includes such a large number of people. However, he is not sure about the link to melanoma because of the difficulties in interpreting findings for specific pesticides, even with such a large amount of data.
Chief of epidemiology at the National Institute of Environmental Health Sciences and a co-investigator on the study, Dale Sandler, Ph.D., believes that the findings could have implications for the rest of the population. Some of the chemicals are also used in non-agricultural settings, such as carbaryl, which is also used extensively by homeowners, primarily for lawn care. One major difference, Dr. Sandler points out, is that the workers use protective equipment, potentially making relatively lower doses risky for residential users.
“The applicators receive continuing education to learn about safe handling of these chemicals, but you or I may go to the store and not read the label,” Dr. Sandler added. Surveys, including one published last month have shown that vague pesticide labels can cause consumers to misapply pesticides.
However, the risks also go beyond the workers or consumers who use the pesticides. Often the chemicals are in the environment near farms and can contaminate groundwater, Dr. Sandler said. Many of the active ingredients are used in combination, which makes it difficult to identify the risky ones. Studies show that many pesticides have dangerous synergistic effects when exposure is combined with other pesticides and pharmaceuticals. Other research has found that even if the concentration of the individual chemicals are within limits considered safe, when more than one pesticide is combined, it can create a toxic mixture that has adverse effects on wildlife and the environment.