Passing along pesticides: lymphoma rises in children of applicators.

A growing body of scientific evidence suggests there may be an association between parents' exposure to pesticides and cancer in their children. In this issue, Kori Flower of the University of North Carolina--Chapel Hill School of Public Health and colleagues report the results of their recent study investigating the possibility of increased cancer risk among the children of pesticide applicators [EHP 112:631-635]. The associations they uncovered, although modest, underscore the need for careful evaluation of this issue.

The authors used detailed parental pesticide application data derived from questionnaires gathered by the Agricultural Health Study, a large prospective study of pesticide applicators and their spouses in Iowa and North Carolina conducted by the NIEHS, the National Cancer Institute, and the U.S. Environmental Protection Agency. Flower and colleagues limited their study to Iowa workers and their families. The 52,395 Iowa pesticide applicators who enrolled in the Agricultural Health Study between 1993 and 1997 accounted for a total of 17,357 children born during or after 1975. By linking information about those children with data from the Iowa Cancer Registry, the researchers were able to identify 50 cases of cancer among children of Iowa pesticide applicators.

The team compared the cancer incidence rate in the cohort to that expected in the general population to generate a standardized incidence ratio, and found an increased cancer incidence rate among children of the Iowa workers. The risk of all childhood cancers combined was 36% greater in children of applicators compared to all Iowa children; the risk of all lymphomas more than doubled, and that of Hodgkin lymphoma was 2.5 times greater. Further, the team found an increased risk of cancer among children of pesticide applicators who did not wear chemical-resistant gloves during application, as opposed to the children of those who did. As the authors point out, this could indicate direct pesticide exposure in the applicators (who would then carry the chemicals home) or less meticulous chemical practices on the farm, both of which could increase the opportunity for exposure among the children.

What the authors didn't find may be just as interesting as what they did. For example, no association was found between frequency of parental pesticide application and increased childhood cancer risk, nor was there evidence of a dose--response relationship between parental exposure and children's risk. Although those findings may have been due to the small number of cases involved and the resulting limited statistical power, the investigators stress that "the possibility that increased cancer risk within the cohort is unrelated to pesticide exposure must be considered."

Of the 50 specific pesticides studied, exposure to 1 was significantly associated with increased cancer risk: Flower and colleagues detected a 2.5-fold greater cancer risk in association with exposure to aldrin prior to conception. However, aldrin has not been clearly linked to human cancer. No significant associations were detected between exposure to classes of pesticides (organophosphates, organochlorines, carbamates, chlorphenoxy compounds, pyrethroids) and increased risk.

Despite the limitations of the study, Flower and colleagues point out that "the identification of excess lymphoma risk suggests that farm exposures including pesticides may play a role in the etiology of childhood lymphoma." That conclusion underscores the need for larger studies to clarify potential cancer risks from pesticides.