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.