Global patterns of human exposure to flame retardants indoors

To fill the knowledge gaps regarding the global patterns of human exposure to flame retardants (FRs) (i.e., brominated flame retardants (BFRs) and organophosphorus flame retardants (OPFRs)), data on the levels and distributions of FRs in external and internal exposure mediums, including indoor dust, indoor air, skin wipe, serum and urine, were summarized and analysed. Comparatively, FR levels were relatively higher in developed regions in all mediums, and significant positive correlations between FR contamination and economic development level were observed in indoor dust and air. Over time, the concentration of BFRs showed a slightly decreasing trend in all mediums worldwide, whereas OPFRs represented an upward tendency in some regions (e.g., the USA and China). The occurrence levels of FRs and their metabolites in all external and internal media were generally correlated, implying a mutual indicative role among them. Dermal absorption generally contributed >60% of the total exposure of most FR monomers, and dust ingestion was dominant for several low volatile compounds, while inhalation was found to be negligible. The high-risk FR monomers (BDE-47, BDE-99 and TCIPP) identified by external exposure assessment showed similarity to the major FRs or metabolites observed in internal exposure mediums, suggesting the feasibility of using these methods to characterize human exposure and the contribution of indoor exposure to the human burden of FRs. This review highlights the significant importance of exposure assessment based on multiple mediums for future studies.