Occupational Exposure to Pesticides and Chronic Lymphocytic Leukaemia in the MCC-Spain Study

We aimed to study the association between occupational exposure to pesticides and chronic lymphocytic leukemia (CLL) in Spain. Occupational exposure to pesticides (four insecticides, four herbicides and two fungicides) was evaluated using a job-exposure matrix for the Spanish population (MatEmESp) among 302 CLL cases and 1567 population controls in five regions of Spain, 2010-2013. Cumulative exposure scores (CES) were obtained by summing across the exposed jobs the product of prevalence, intensity and duration of exposure to each active substance. Principal components analysis (PCA) and logistic regression models adjusted for age, sex, region, education and occupational exposure to solvents were used. Around 20% of controls and 29% of cases were exposed to one or more pesticides. Compared to non-exposed, subjects in the highest tertile (3rd tertile) of CES of insecticides, herbicides, fungicides were more likely to have CLL [OR (95% CI), P-trend; 2.10 (1.38; 3.19), 0.002; 1.77 (1.12; 2.80), 0.12; and 1.67 (1.06; 2.64), 0.10, respectively). Following PCA, the first component (PC1, explaining 70% of the variation) equally led by seven active substances (the insecticide pyrethrin, all herbicides, all fungicides) was associated with a 26% higher odds of having CLL for 1-standard deviation increase in PC1 (95% CI: 1.14 to 1.40). These results confirm previous associations between CLL and exposure to pesticides and provide additional evidence by application groups and active substance. However, more research is needed to disentangle independent effects of individual active substances.