Quantitative Measurement of Phthalate Exposure Biomarker Levels in Diaper-Extracted Urine of Japanese Toddlers and Cumulative Risk Assessment: An Adjunct Study of JECS Birth Cohort

Associations of 1.5- and 3-year phthalate exposure levels with early adiposity rebound and overweight/obesity in Japanese children: An adjunct study of the Japan Environment and Children's Study

The relationship between early childhood phthalate exposure and early adiposity rebound (EAR) is unclear. This study aimed to investigate the association between 1.5- and 3-year phthalate exposure and EAR and overweight/obesity in 7.5-year-old Japanese children. A total of 452 mother-child pairs were enrolled from the Aichi Regional Cohort of the Japan Environment and Children's Study. The children were followed up at birth and at 1.5, 2, 3, 4, 5, 6, and 7.5 years of age for physical examination. Human biomonitoring of 16 urinary metabolites of eight phthalates was performed at 1.5 and 3 years of age. Latent class mixed models, binary logistic regression, and quantile g-computation were performed to identify body mass index (BMI) trajectories and investigate the relationships of single or mixed phthalate exposure with EAR and overweight/obesity. A one-unit increase in log10-transformed 3-year-old Σdi(2-ethylhexyl) phthalate (ΣDEHP) exposure levels was significantly associated with 6-year-old BMI in girls. The 1.5-year mono-iso-butyl phthalate and 3-year Σdi-isodecyl phthalate exposure levels were significantly associated with the repeated measures of longitudinal BMIs in girls. Single phthalate exposure showed null associations with EAR or overweight/obesity in the 7.5-year-old children. Σdi-isononyl phthalate, ΣDEHP, and mono-n-butyl phthalate exhibited the highest proportion of partial positive weights of being in the EAR trajectory after confounder adjustment. Phthalate mixture exposure in 1.5- and 3-year-old children was not significantly associated with EAR. Early childhood phthalate exposure was not related to EAR or overweight/obesity in 7.5-year-old Japanese children. However, few phthalates were positively associated with longitudinal BMIs in girls.

Assessment of baby disposable diapers application for urine collection and determination of phthalate metabolites

The baby disposable diapers were investigated as a sampling material for urine collection and validated for the evaluation of the exposure of children to xenobiotics. Phthalate metabolites detected in urine samples were chosen as proof-of-concept analytes. For the determination of phthalate metabolites in children's urine samples, high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) was used. Two sampling approaches were compared, namely sterile containers and baby disposable diapers. Thirty urine samples from infants and toddlers were analyzed by both methods in parallel and the results were compared. It was found that for diaper sampling, lower concentrations of the metabolites were observed, however, the general distribution for particular metabolites remains the same for both methods. For most of the metabolites high determination coefficients were obtained, namely 0.9929 for MEHHP, 0.9836 for MMP, 0.9796 for MECPP, and 0.9784 for 2-cx-MMHP. For MEOHP the determination correlation coefficient was 0.9154, while for MBP was - 0.7771 and MEHP was - 0.5228. In general, for diaper sampling an underestimation for 2-cx-MMHP and MEOHP was observed, while for MMP diaper-based approach provides overestimation. However, the proposed procedure confirms the possibility of using baby disposable diapers as a material for the collection of urine samples for biomonitoring purposes and fast screening of phthalates exposure.