Human exposure pathways to organophosphate triesters — A biomonitoring study of mother–child pairs

• Urinary concentrations of BDCIPP and DPHP were higher for children than for mothers.
• Concentrations of metabolites in urine correlated with organophosphates in dust and air.
• Exposure of children to organophosphates can be related to indoor environment.
• Diet seems to play a minor role for exposure to organophosphate flame retardants.
• Morning urine reflects well the 24 hour average excretion of BDCIPP and DPHP.

The worldwide ban of several formulations of brominated flame retardants has caused an increase in the production of organophosphorus flame retardants (PFRs) to meet the existing fire regulations for a wide range of household products. This biomonitoring study surveys the occurrence of the metabolites from PFRs and related plasticizers (dialkyl and diaryl phosphates; DAPs) in urine from a Norwegian mother–child cohort (48 mothers and 54 children). Concentrations of DAPs were higher in the children than in their mothers (Wilcoxon signed-rank test p = 0.001). Median urinary concentrations of diphenyl phosphate (DPHP) were 1.1 and 0.51 ng/mL in children and mothers, respectively, followed by bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) with medians of 0.23 and 0.12 ng/mL, respectively. Detection frequencies for bis(2-butoxyethyl) phosphate (BBOEP) in urine from children and mothers were 32 and 1%, respectively (median < 0.18 ng/mL), and for di-n-butyl phosphate (DNBP) 15 and 8%, respectively (median < 0.12 ng/mL). The concentrations of DPHP and BDCIPP in urine from children were significantly correlated with those found for their parent compounds in air and dust from the households (Spearman's rank correlations 0.30 < Rs < 0.36; p < 0.05). For mothers, only the urinary concentration of BDCIPP was correlated to its precursor in dust from the households (Rs = 0.40; p < 0.01), which might indicate higher impact of the household environment on children than mothers. A diurnal variability study of the mothers' urinary concentrations of DPHP and BDCIPP showed lower concentrations at time periods when women were likely to be outside the household. In contrast, no relevant associations between organophosphate metabolites in urine and food consumption data obtained through a 24 hour recall were seen. This suggests that the residential environment is a more important exposure pathway to PFRs than the diet.