Strength in Numbers: 
Three Separate Studies Link in Utero Organophosphate Pesticide Exposure and Cognitive Development

Children entering classrooms for the first time this fall can be seen carrying backpacks filled with school supplies, yet each new student brings something less obvious but more important—a legacy of their earlier experiences and environment. Three studies published in this issue of Environmental Health Perspectives (Bouchard et al. 2011; Engel et al. 2011; Rauh et al. 2011) deliver compelling new data link­ ing one aspect of a child's history—in utero exposure to organophos­ phates (OP), a commonly used class of pesticides—and early cognitive develop ment. Working memory, perceptual reasoning, and IQ were among the measures of intellectual develop ment associated with pre­ natal OP exposure. Bouchard et al. (2011) found that children in the category corresponding to the highest 20% of maternal urinary levels of OP metabolites during pregnancy showed a 7­point decrease in full scale IQ compared with children of mothers in the lowest 20%, an association of magnitude similar to that observed with an increase in blood lead concentrations from 1 to 10 µg/dL (Canfield et al. 2003). The strength of evidence arising from these studies reflects, in part, their rigorous study design. Each used a longitudinal birth cohort, a design well suited to detect the evolution of exposure effects over time. Accordingly, the latest findings build on previous data from these birth cohorts showing relationships between pre natal OP pesticide exposure levels and develop mental end points in the first 3 years of life (e.g., Engel et al. 2007; Eskenazi et al. 2004; Rauh et al. 2006). Decrements in full­scale IQ, working memory, and perceptual rea­ soning showed the most consistent associations with pre natal exposure biomarkers across studies. Comparability of these results, despite dif­ ferences in populations and exposure metrics, underscores the robust­ ness of this latest group of findings. Two of the birth cohorts represent multi ethnic inner city populations in New York City, while the third cohort comprises low­income families living in California's Salinas Valley, an agricultural area. Rauh et al. (2011) meas ured chlorpyrifos in cord blood, whereas Engel et al. (2011) and Bouchard et al. (2011) relied on measure ment of non specific OP metabolites in maternal urine samples collected during pregnancy. A primary limitation of these three studies relates to exposure assess­ ment. One study measured chlorpyrifos and diazinon in blood (Rauh et al. 2011), but the other studies (Bouchard et al. 2011; Engel et al. 2011) meas ured OP …