Variability of urinary pesticide metabolite concentrations during pregnancy in the MARBLES Study

Background: Variability of short-lived urinary pesticide metabolites during pregnancy raises challenges for exposure assessment. Objectives: For urinary metabolite concentrations 3-phenoxybenzoic acid (3-PBA) and 3,5,6-trichloro-2-pyridinol (TCPy), we assessed: (1) temporal variability; (2) variation of two urine specimens within a trimester; (3) reliability for pesticide concentrations from a single urine specimen to classify participants into exposure tertiles; and (4) seasonal or year variations. Methods: Pregnant mothers (N = 166) in the MARBLES (Markers of Autism Risk in Babies-Learning Early Signs) Study provided urine specimens (n = 528). First morning void (FMV), pooled, and 24-h specimens were analyzed for 3-PBA and TCPy. For 9 mothers (n = 88 specimens), each urine specimen was analyzed separately (not pooled) to estimate within- and between-person variance components expressed as intraclass correlation coefficients (ICC). Pesticide concentrations from two specimens within a trimester were also assessed using ICC's. Agreement for exposure classifications was assessed with weighted Cohen's kappa statistics. Longitudinal mixed effect models were used to assess seasonal or year variations. Results: Urinary pesticide metabolites were detected in >= 93% of specimens analyzed. The highest ICC from repeated individual specimens was from specific gravity-corrected FMV specimens for 3-PBA (ICC = 0.13). Despite high within-person variability, the median concentrations did not differ across trimesters. Concentrations from pooled specimens had substantial agreement predicting exposure categories for TCPy (K = 0.67, 95% CI (0.59, 0.76)) and moderate agreement for 3-PBA (K = 0.59, 95% CI (0.49, 0.69)). TCPy concentrations significantly decreased from 2007 to 2014. Conclusions: Pooled specimens may improve exposure classification and reduce laboratory costs for compounds with short biological half-lives in epidemiological studies.