Pesticides
IARC has classified different pesticides as definite, probable or possible carcinogens to humans. Studies in experimental animals, in vitro test systems and humans occupationally exposed to pesticides have shown DNA damage (oxidative DNA damage, DNA strand breaks) or chromosomal damage (micronuclei), indicating the potential genotoxicity of these chemicals even though regulatory genetic toxicity tests are generally negative. The biological plausibility of the intrauterine exposure to pesticides lies in their effect on oxidative stress, which may cause DNA single- and double-strand breaks in fetal hematopoietic stem and progenitor cells at specific cleavage sites. These lesions, if mis-repaired may lead to chromosomal translocations involved in the regulation of early hematopoiesis. More recent studies on epigenetics have also shown that pesticide exposure during the critical period of pregnancy may detrimentally alter the epigenome and gene expression profile of stem cells, positioning these cells for malignant transformation. Our results are in line with recent systematic reviews and meta-analyses which have shown that pesticide, especially insecticide exposure during pregnancy increases the risk of childhood leukemia, particularly among infants. Yet, we should acknowledge that pesticides have mainly been studied as groups, sometimes divided into insecticides, herbicides and fungicides, but still lumping chemically distinct active ingredients and formulations, which likely range from harmful to harmless. More research is needed to identify those products within pesticides that are associated with an increased risk of different cancer types.