Residential Pesticides and Childhood Leukemia: A Systematic Review and Meta-Analysis
Many Canadian municipalities or provinces have banned or restricted cosmetic pesticide use and other jurisdictions are considering similar bans or facing continuous public pressure for such action. Major public and scientific concerns about pesticides include their potential adverse effects on child health and development. Of the 15 most intensely used pesticides in the U.S. during 2001, five are classified as probable and five as possible human carcinogens. Use of specific or mixed pesticides has been linked to lymphocyte and sperm DNA damage detectable by the Comet assay in occupationally exposed men.
Leukemia is the most common childhood cancer; the only proven modifiable risk factor is prenatal or childhood exposure to ionizing radiation. Most cases have gross chromosomal abnormalities including translocations caused by faulty repair of double-strand DNA breaks and probably have a clonal origin in utero. Preleukemic clones may persist during childhood with only a minority progressing to leukemia. Postnatal exposures may be required for such progression.
Previous reviewers found fairly consistent epidemiological evidence for an association between childhood leukemia and parental or childhood pesticide exposure, especially indoor insecticides; however, a number of limitations with existing studies were noted. The goal of this review was to quantitatively synthesize the epidemiological evidence for an association between parental or childhood pesticide exposure and childhood leukemia risk with a view toward defining and assessing issues important to public health practitioners and identifying knowledge gaps. A thorough search identified relevant original research reports in peer-reviewed journals and dissertations. The two lead authors (DW and MT) independently rated the quality of the studies using predefined criteria.
Based on meta-analyses of relevant studies childhood leukemia was positively associated with prenatal maternal occupational pesticide exposure (summary OR = 2.09, 95% CI, 1.51-2.88), but not paternal occupational pesticide exposure (Wigle et al., 2009). Prenatal maternal exposure to residential pesticides was also positively associated with childhood leukemia, particularly insecticides (summary OR = 2.05, 95% CI, 1.80-2.32) (Turner et al., 2010). Several research needs were identified: (i) improved and validated pesticide exposure assessment tools for epidemiological studies; (ii) financial support for continuation of existing well-designed cohort studies; such as, the U.S. Agricultural Health Study and follow-up studies of the children of occupationally exposed parents in such cohorts; (iii) funding for new case-control and cohort studies with sufficient statistical power to assess major childhood leukemia subtypes (ALL, AML), enhanced exposure assessment (validated measures of exposure to specific or closely related pesticides including intensity and timing/duration of exposure), exposure-risk gradient analyses, and measurement of genetic susceptibility markers.