Organophosphate Esters and Their Metabolites in Breast Milk from the United States: Breastfeeding Is an Important Exposure Pathway for Infants

Organophosphate esters (OPEs) are among the synthetic chemicals found in the highest concentrations in the indoor environment due to their use as flame retardants and plasticizers. In fish and wildlife, metabolites of OPEs have been found to build up in tissues. In this study, 28 triester OPEs (tri-OPEs) and their seven corresponding diester (di-OPE) and three hydroxyl metabolites were measured in breast milk collected from 50 U.S. mothers. Tris(1-chloro-2-propyl) phosphate, used in foam for insulation and furniture and the target compound with the largest U.S. production volume, was the most abundant tri-OPE (median level of 1.47 ng/mL). Di-n-butyl phosphate (DNBP), the metabolite of tri-n-butyl phosphate (TNBP), which has broad uses in adhesives, plastics, and hydraulic fluids, was the most abundant OPE metabolite (median level of 7.44 ng/mL) detected in these samples. Overall, the Sigma di-OPE concentrations (median level of 8.32 ng/mL) were twice as high as the Sigma tri-OPE concentrations (median of 3.85 ng/mL). The estimated daily intakes of tri- and di-OPEs through lactation were up to 50 times higher than those through diet and dust ingestion. This is the first study to simultaneously determine OPEs and their metabolites in breast milk, and our findings indicate that breastfeeding is a significant source of OPE exposure for infants.

Automated summary

Organophosphate esters (OPEs) are synthetic chemicals found in high concentrations in the indoor environment, and their metabolites were detected in breast milk from U.S. mothers. The study found that diester OPE concentrations were twice as high as triester OPE concentrations, and breastfeeding is a significant source of OPE exposure for infants. The most abundant OPE in breast milk was tris(1-chloro-2-propyl) phosphate, while the metabolite di-n-butyl phosphate (DNBP) was the most abundant OPE metabolite detected in the samples.