CATEGORY*: Endocrine disruptors, Chlordane: IARC possible carcinogen
FOUND IN: Agricultural and household pest control
THE GIST: Pesticides are frequently used in combinations, which means that most human studies of pesticide use have studied the health effects of mixtures. Studies of Latina agricultural workers, and of agricultural families have found increased breast cancer risk among these groups. These risks may be highest among women exposed at a young age. Studies also found stronger associations to early-onset breast cancer.
State of the Evidence on Other Pesticides
For some pesticides, the strongest evidence for concern has emerged from human studies of agricultural workers and their families. Real-life use of pesticides often means using more than one pesticide at a time. This makes it challenging to tease out whether observed effects on health are a result of the mixture of chemicals or if one of the pesticides is the culprit. Regardless, these findings underscore the need to use pesticides with great caution, since they can impact the health of workers and communities.
A case-control study of 128 Latina agricultural workers newly diagnosed with breast cancer in California identified three pesticides—chlordane, malathion and 2,4-D—associated with an increased risk of the disease. Scientists found that the risks associated with use of these chemicals were higher in young women and in those with early-onset breast cancer than in unexposed women (Mills, 2005).
In a study of rat mammary tissue development, malathion treatment led to increased proliferation of mammary cells as well as increased development of ductal mammary cancers. Concurrent treatment of rats with both malathion and the natural estrogen estradiol led to increased incidence of both ductal and lobular types of mammary cancers (Calaf, 2011).
Researchers from the National Cancer Institute studied the association between pesticide use and breast cancer risk in farmers’ wives in the Agricultural Health Study. This large prospective cohort study enrolled more than 30,000 women in Iowa and North Carolina. Researchers found evidence of increased incidence of breast cancer in women exposed to 2,4,5-trichlorophenoxypropionic acid (2,4,5-TP) and possibly in women exposed to dieldrin and the fungicide ethanethiol (captan), although the small number of cases among those who had personally used pesticides precluded firm conclusions. Incidence was also modestly elevated in women whose homes were closest to areas of pesticide application (Engel, 2005).
A recent study of farmers and their families shows that young children of farmers using 2,4,5-TP on their farms had high levels of the pesticide in their urine samples soon after the chemical had been applied to the fields (Alexander, 2007). This is of concern, given the evidence of increased susceptibility of children and young adolescents to the carcinogenic effects of chemicals.
*For chemicals that have been shown to be carcinogens, we provide classifications from two authoritative bodies: the International Agency for Research on Cancer (IARC, an international body) and the National Toxicology Program (NTP, a division of the U.S. Department of Health and Human Services). We have categorized endocrine-disrupting compounds where the body of peer-reviewed research indicates a strong foundation for doing so.