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Due to the complex nature of studying human diseases, much of the research linking pesticides and cancer has been done in the laboratory with animals. According to these studies, many pesticides are confirmed carcinogens. In addition to lab studies, epidemiologic research studying the effects of pesticides on agricultural workers has uncovered a strong link between increased risk for cancer and pesticide exposure. Scientists continue to examine herbicides, fungicides and insecticides to better understand the connection between these pesticides and increased risks for developing cancer. A link between home use of pesticides and cancer is another area of continuing research.
The organochlorine class of insecticides that contains dichlorodiphenyltrichloroethane (DDT), heptachlorine and lindane, has been suspected as potentially carcinogenic for decades. Although many of these pesticides have been banned in the numerous countries, others are still in use. These chemicals have a tendency to accumulate in the living tissues of plants and animals and are persistent in the environment. Food samples show that the banned chemicals are even present in the current food supply. Some researchers believe environmental exposure to pesticides through food, water and air plays a role in the development of cancer.
Contaminated breast tissue in women with breast cancer is sited as evidence of a link between pesticides and cancer. Higher than expected levels of pesticide chemicals have been found in the diseased tissue. Some cancer organizations have stated there is insufficient evidence to establish a clear link between breast cancer and chemicals such as pesticides, while other researchers claim a firm connection between increased pesticide exposure and breast and other cancers. There is some evidence that the hormone-mimicking properties of certain pesticides might explain the link between these chemicals and the increased risk for hormone sensitive cancers such as breast, uterine and ovarian cancer.
Large epidemiologic studies of agricultural workers have shown that increased exposure to some pesticides appears to increase the risk of melanoma. Sun exposure also plays a part in the development of this cancer, making clear evidence of a link between pesticides and cancer difficult. Other cancers linked to agricultural pesticide use include malignant lymphoma, non-Hodgkin’s lymphoma and leukemia. Researchers continue to examine the link between pesticides and cancer of the lung and ovaries.
In addition to studies of agricultural workers, home use and environmental exposure to pesticides have also been linked to an increased risk of some cancers. Some pesticide products used in the garden and home have been associated with a greater incidence of cancer. Epidemiology has uncovered suspected connections between childhood cancers and exposure to pesticides. Organophosphate insecticides and herbicides are of particular concern. Due to the complex nature of studying human disease, there is conflicting evidence for many of the links between pesticides and cancer, including in studies of chemicals commonly used by consumers around the home.