Pesticide Residues in Food and Cancer Risk : A Critical Analysis

Possible cancer hazards from pesticide residues in food have been much discussed and hotly debated in the scientific literature, the popular press, the political arena, and the courts. Consumer opinion surveys indicate that much of the U.S. public believes that pesticide residues in food are a serious cancer hazard (Opinion Research Corporation, 1990). In contrast, epidemiologic studies indicate that the major preventable risk factors for cancer are smoking, dietary imbalances, endogenous hormones, and inflammation (e.g., from chronic infections). Other important factors include intense sun exposure, lack of physical activity, and excess alcohol consumption (Ames et al., 1995). The types of cancer deaths that have decreased since 1950 are primarily stomach, cervical, uterine, and colorectal. Overall cancer death rates in the United States (excluding lung cancer) have declined 19% since 1950 (Ries et al., 2000). The types that have increased are primarily lung cancer [87% is due to smoking, as are 31% of all cancer deaths in the United States (American Cancer Society, 2000)], melanoma (probably due to sunburns), and non-Hodgkin’s lymphoma. If lung cancer is included, mortality rates have increased over time, but recently have declined (Ries et al., 2000). Thus, epidemiological studies do not support the idea that synthetic pesticide residues are important for human cancer. Although some epidemiologic studies find an association between cancer and low levels of some industrial pollutants, the studies often have weak or inconsistent results, rely on ecological correlations or indirect exposure assessments, use small sample sizes, and do not control for confounding factors such as composition of the diet, which is a potentially important confounding factor. Outside the workplace, the levels of exposure to synthetic pollutants or pesticide residues are low and rarely seem toxicologically plausible as a causal factor when compared to the wide variety of naturally occurring chemicals to which all people are exposed (Ames et al., 1987, 1990a; Gold et al., 1992). Whereas public perceptions tend to identify chemicals as being only synthetic and only synthetic chemicals as being toxic, every natural chemical is also toxic at some dose, and the vast proportion of chemicals to which humans are exposed are naturally occurring (see Section 38.2). There is, however, a paradox in the public concern about possible cancer hazards from pesticide residues in food and the lack of public understanding of the substantial evidence indicating that high consumption of the foods that contain pesticide residues—fruits and vegetables—has a protective effect against many types of cancer. A review of about 200 epidemiological studies reported a consistent association between low consumption of fruits and vegetables and cancer incidence at many target sites (Block et al., 1992; Hill et al., 1994; Steinmetz and Potter, 1991). The quarter of the population with the lowest dietary intake of fruits and vegetables has roughly twice the cancer rate for many types of cancer (lung, larynx, oral cavity, esophagus, stomach, colon and rectum, bladder, pancreas, cervix, and ovary) compared to the quarter with the highest consumption of those foods. The protective effect of consuming fruits and vegetables is weaker and less consistent for hormonally related cancers, such as breast and prostate. Studies suggest that inadequate intake of many micronutrients in these foods may be radiation mimics and are important in the carcinogenic effect (Ames, 2001). Despite the substantial evidence of the importance of fruits and vegetables in prevention, half the American