Glyphosate in house dust and risk of childhood acute lymphoblastic leukemia in California

Background/Aim: In prior analyses in the California Childhood Leukemia Study (CCLS), house dust concentrations of the herbicide dacthal were associated with acute lymphoblastic leukemia (ALL). Here, we estimated ALL risk with concentrations of glyphosate in homes. Methods: The CCLS is a population-based case-control study of childhood leukemia (<15 years) in 35 counties in the Central Valley/San Francisco Bay area. Among those <8-years (no move since diagnosis/reference date), we collected dust (2001-2007) from the room where the child spent the most time while awake and measured >40 pesticides. Three-to-eight years later, we collected a second sample from non-movers. We used Ultra-Performance Liquid Chromatography Tandem Mass Spectrometry to measure glyphosate (µg/g dust) for 181 ALL cases and 225 controls and for 45 cases/controls with a second dust sample. Odds ratios (ORs) and 95% confidence intervals (CI) were calculated for quartiles of the concentration (first sample) using unconditional logistic regression. We computed the intraclass correlation coefficient (ICC), the within-to-between home variance ratio, and bias in a true OR=2.0 based on one dust sample. Results: Glyphosate was frequently detected (cases: 98%; controls: 99%). Higher concentrations in homes were associated with occupational pesticide exposure among family members, nearby agricultural use, treatment for lawn weeds and bees/wasps, and season. Increasing concentrations in the homes were not associated with ALL risk (adjusted ORQ4vs.Q1=0.8 CI 0.4-1.4). We observed similar null associations for boys and girls, Hispanics and non-Hispanic whites, and among those who resided in their home since birth (76 cases/117 controls) or age two (130 cases/176 controls). The ICC was 0.32 and the variance ratio was 2.13, which would result in a biased OR=1.25 based on one sample. Conclusions: Glyphosate concentrations in homes were not associated with risk of childhood ALL. Due to large within-home temporal variability in concentrations, a modest association cannot be ruled out.