Organophosphate pesticide metabolite concentrations in a pregnancy cohort: daily variability, and predictors of exposure

Organophosphates (OP) are commonly used agricultural pesticides. In 2009-2010, 80 pregnant women were recruited from Ottawa, Canada for the Plastics and Personal-care Product use in Pregnancy (P4) Study. A subset (n = 25) collected multiple spot urines (up to 10 each; total n = 431) over two 24-h periods in early pregnancy - one weekday and weekend day - while logging their food consumption beginning 24 h prior to the first urine void and continuing through the following 24-h urine collection period. Urine samples (n = 431 samples) were analyzed for six dialkyl OP metabolites, dimethyldithiophosphate (DMDTP), dimethylthiophosphate (DMTP), dimethylphosphate (DMP), diethyldithiophosphate (DEDTP), diethylthiophosphate (DETP), and diethylphosphate (DEP). This is the first study to look at within day variability of OP pesticide metabolites. Intra-class correlation coefficients (ICC's) were highest for DMP on weekend days (0.82) and lowest for DEDTP (0.35). Using a single spot urine to predict high urinary concentrations compared to the geometric mean of the participant's remaining samples for that day showed median sensitivities ranging from 67 to 87 % (weekday) and 73-81 % (weekend). This study was underpowered to see clear group differences; however molar sum dialkyl phosphate (DAP) metabolite concentrations over the 24 h weekday collection period increased or remained stable in urine samples collected >6-12 h post-consumption of most food groups. We encourage future research with a larger sample size and more diverse participants, with a focus on OPs that are increasing or remaining stable over time including DEP and metabolites of pyrethroids, and neonicotinoids.