Structure-activity relationships of chemicals causing endocrine, reproductive, neurotoxic, and oncogenic effects--a public health problem

Residential proximity to agricultural pesticide use and incidence of breast cancer in California, 1988-1997

California is the largest agricultural state in the United States and home to some of the world's highest breast cancer rates. The objective of our study was to evaluate whether California breast cancer rates were elevated in areas with recent high agricultural pesticide use. We identified population-based invasive breast cancer cases from the California Cancer Registry for 1988-1997. We used California's pesticide use reporting data to select pesticides for analysis based on use volume, carcinogenic potential, and exposure potential. Using 1990 and 2000 U.S. Census data, we derived age- and race-specific population counts for the time period of interest. We used a geographic information system to aggregate cases, population counts, and pesticide use data for all block groups in the state. To evaluate whether breast cancer rates were related to recent agricultural pesticide use, we computed rate ratios and 95% confidence intervals using Poisson regression models, adjusting for age, race/ethnicity, and neighborhood socioeconomic status and urbanization. This ecologic (aggregative) analysis included 176,302 invasive breast cancer cases and 70,968,598 person-years of observation. The rate ratios did not significantly differ from 1 for any of the selected pesticide categories or individual agents. The results from this study provide no evidence that California women living in areas of recent, high agricultural pesticide use experience higher rates of breast cancer.

Residential proximity to agricultural pesticide use and incidence of breast cancer in the California Teachers Study cohort

We examined the association between residential proximity to agricultural pesticide use and breast cancer incidence among members of the California Teachers Study cohort, a large study of professional school employees with extensive information on breast cancer risk factors, followed for cancer incidence since 1995. We identified 1552 invasive breast cancer cases, diagnosed between 1996 and 1999, among 114,835 cohort members. We used California Pesticide Use Reporting data to select pesticides for analysis based on use volume, carcinogenic potential, and exposure potential; a Geographic Information System was used to estimate pesticide applications within a half-mile radius of subjects' residences. We applied Cox proportional hazard models to estimate hazard rate ratios (HR) for selected pesticides, adjusting for age, race, and socioeconomic status. We saw no association between residential proximity to recent agricultural pesticide use and invasive breast cancer incidence. HR estimates for the highest compared to the lowest exposure categories for groups of agents were as follows: probable or likely carcinogens (1.07, 95% confidence interval (CI): 0.86-1.32), possible or suggestive carcinogens (1.06, 95% CI: 0.87-1.29), mammary carcinogens (1.15, 95% CI: 0.90-1.48), and endocrine disruptors (1.03, 95% CI: 0.86-1.25). HR estimates for other groups and individual pesticides did not differ from unity, nor was there a trend for any groupings of or individual pesticides examined. Stratifying by menopausal status or family history of breast cancer did not substantially affect our results. Our analyses suggest that breast cancer incidence is not elevated in areas of recent, high agricultural pesticide use in California.

Ames, pesticides, and cancer revisited

The case for continuing use of existing levels of pesticides in agriculture, espoused by Bruce Ames, is refuted. Ames' contentions that naturally occurring carcinogens are far more widespread than man-made ones, that pesticides prevent cancer by providing fruits and vegetables at lower costs to the poor, and that animal data on high risks with high doses cannot predict low risks from low doses in humans do not address key issues: 1) fruits and vegetables contain mixtures of carcinogens and anti-carcinogens, and selection effects from human exposures to these mixtures go back more than a million years; 2) exposures from bioconcentrations of biopersistent organochlorines in the food chain create particular risks for meat-eaters, who have higher cancer risks than vegetarians; 3) even low doses from ingestion of produce containing pesticide residues can cause tissue injury, which could itself promote cancer; 4) epidemiologic data show rises in cancer incidences in older people in many countries, major differences in cancer risks between countries, and converging trends in risks for populations migrating to certain countries; 5) studies of pesticide-exposed workers consistently show increased rates of cancers and birth defects and cancers in their offspring; 6) epidemiologic studies based on large databases tend to underestimate risks from environmental causes because of exposure misclassification; 7) exposures to many organochlorines may have pervasive effects on endocrine function; 8) crop yields can be increased with less use of pesticides. Studies demonstrating the latter need replication, and should be supported as part of a coherent government agenda to develop alternative farming methods.