The researchers found that even though melanoma was infrequent among the studied workers, it increased in frequency among those most highly exposed to several of the pesticides.
Of the 56,285 people studied, 271, or less than half of one percent, developed melanoma. Risks of the disease increased 2.5 times for applicators exposed to more than 63 days of maneb/mancozeb in their lifetime. Applicators who were exposed carbaryl more than 56 days were 1.7 times more likely and exposure to either methyl or ethyl parathion more than 56 days increased their melanoma risks by 2.4 times.
The findings could have meaning for the rest of the population, said Dale Sandler, chief of epidemiology at the National Institute of Environmental Health Sciences and a co-investigator on the study.
Sandler said that some of the chemicals are used by the general population. One major difference is that the workers use protective equipment. This has the potential to make even 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,” Sandler said.
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, Sandler said.
The company that markets Sevin to the U.S. consumer market, GardenTech, declined to comment on the new study. Bayer Crop Sciences, the U.S. manufacturer of Sevin, could not be reached for comment.
Michael Thun, vice president of epidemiology and surveillance research at the American Cancer Society, said the study is “better equipped than most to tease out data” because it included such a large number of people.
But he still has doubts about the link between specific pesticides and skin cancer.
Thun said that even with such a large amount of data, “it is difficult to interpret findings in regard to specific pesticides.” Many of the active ingredients are used in combination, which makes it difficult to identify the risky ones.
The findings also may have been complicated by the workers’ sun exposure, which is the major risk factor for melanoma.
“Since farmers spend a great deal of time in the sun, we cannot rule out the possibility that these pesticides specific results are driven by sun exposure," the authors said in their report.