A critical review of human internal exposure and the health risks of organophosphate ester flame retardants and their metabolites.

The phasing out of brominated flame retardants from markets has prompted an increased focus on organophosphate ester (OPE) flame retardants because of their wide usage and toxicity. The high usage of OPEs inevitably leads to widespread occurrence in the environment and thus human internal exposure. Accordingly, extensive internal exposure to OPEs and their metabolites (mOPEs) has been reported in recent years. Here, we review literature findings relating to sample pretreatment protocols and instrumental analysis procedures for OPE determination; the occurrence and composition profiles of OPEs and mOPEs in human matrices including urine, blood, milk, nails, hair, and placenta; the health risks associated with OPE exposure; and notable challenges in OPE analysis. Measured urinary concentrations of dialkyl and diaryl mOPEs were relatively high in the USA but comparatively low in Europe and Asia. There have been few studies on OPEs and their hydroxylated metabolites (HO-OPEs) in human matrices. The main OPEs originating from daily necessity products are tris(2-chloroisopropyl) phosphate, tris(1,3-dichloro-2-propyl) phosphate, and triphenyl phosphate, although there are regional differences. Human exposure to OPEs occurs mainly through oral ingestion. Because of the relatively short biological half-lives of OPEs, urinary mOPE concentrations reflect short-term human OPE exposure, while OPE levels in hair and nails better reflect long-term exposure because of the low metabolic activities of OPEs in these matrices. There is a need to develop effective and flexible pretreatment methods and sensitive instrumental analysis protocols for OPEs/mOPEs and to increase the availability of commercial HO-OPE standards. [ABSTRACT FROM AUTHOR]