Childhood leukaemia and parental occupational exposure to pesticides: a systematic review and meta-analysis.

Objective: To conduct a systematic review and meta-analysis of published studies on the association between parental occupational exposure to pesticides and childhood leukaemia.

Methods: Studies were identified from a MEDLINE search through 31 July 2009 and from the reference lists of identified publications. Relative risk (RR) estimates were extracted from 25 studies published between 1985 and 2008. Meta-rate ratio estimates (mRR) were calculated according to fixed and random-effect meta-analysis models. Separate analyses were conducted after stratification for study design, definition of exposure (employment in a farm/agriculture assuming exposure to pesticides versus exposure to pesticides stipulated), exposed parent, window of exposure, type of leukaemia and biocide category.

Results: No statistically significant association between childhood leukaemia and parental occupation as farmers/agricultural workers was observed. When exposure to pesticides was stipulated, positive associations were reported for maternal exposure for all studies combined (mRR: 1.62; 95% CI: 1.22-2.16), in all exposure windows considered and for acute non-lymphocytic leukaemia (ANLL). There was no association with paternal exposure when combining all studies (mRR: 1.14; 95% CI: 0.76-1.69). However, significant increased risks were seen for paternal exposure, in some exposure windows as well as for the biocide category.

Conclusions: The strongest evidence of an increased risk of childhood leukaemia comes from studies with maternal occupational exposure to pesticides. The associations with paternal exposure were weaker and less consistent. These results add to the evidence leading to recommend minimizing parental occupational exposure to pesticides. Our findings also support the need to rely more on studies that clearly stipulate exposure to pesticides rather than those that assume pesticide exposure because of farm/agriculture employment.