The World Bank estimates that occupational exposure to pesticides may exceed 1 billion
people and other surveys have indicated that nearly every person in the United States is either directly or indirectly exposed to pesticides. This includes 50 million Americans—as
estimated by the U.S. Department of Agriculture (USDA)—who drink water that is
intermittently contaminated with pesticides or other agricultural chemicals.
IARC has labeled agricultural insecticides as probable human carcinogens, but only identified two pesticides—arsenic and dioxin—as known human carcinogens. There is a vital public
health need to identify the human carcinogens in the group of pesticides/insecticides that are currently on the market.
The AHS found that 16 percent of farmers had experienced a high-exposure pesticide event, however, 95 percent of these events were not reported to public health authorities. It is
estimated that 25,000 agricultural workers worldwide experience unintentional pesticide
poisoning each year. Seasonal farm workers tend to be at the greatest risk for this type of
exposure, as they do not always receive training in the safe use, storage, and disposal of
pesticides.
Studying pesticides and their resulting health effects has proven to be difficult. To ascertain exposures, their relation to the onset of disease, and eliminate false positives requires a large prospective cohort with frequent exposure to pesticides and other chemicals of interest.
Further, comprehensive exposure assessment requires gathering field toxicity measurements,
as well as medical and family history, occupational history, demographic profiles, and
biologic tissue samples.
The AHS is evaluating 82 of the world’s most frequently used pesticides for exposure-
response associations. The study is focusing on occupationally exposed pesticide applicators
in two important agricultural states—North Carolina and Iowa. As of September 2008, 12
pesticides were observed to show an increased risk of some cancer with increasing use of the
pesticide. Significant associations were observed for prostate, lung, bladder, pancreas, and
colon cancer, as well as for leukemia and multiple myeloma. However, these associations
were based on a limited number of cases and replication of these first-time findings are
needed.
Indianapolis, IN
2
October 21, 2008
Pesticide carcinogenicity extends beyond lymphomas, leukemias, multiple myeloma, and
prostate cancer, but the lifestyle of farmers may mask some of these associations. Farmers
smoke less and exercise more than the general population and consequently have lower rates
of lung and colon cancer.
Most pesticides are observed to have an exposure response linked to some human cancers,
but are not genotoxic. Therefore, epigenetic events—heritable associations with gene and
chromatin expression without the accompanying change in the DNA sequence—need to be
explored. Current premarket regulatory testing of pesticides may need to be reevaluated due
to the heavy reliance on genotoxicity testing, and postmarket surveillance of the adverse
effects of pesticides needs to be enhanced.
DR. PEGGY REYNOLDS:
AGRICULTURAL EXPOSURES AND CHILDHOOD CANCER