Temporal variations of PM-bound organophosphate flame retardants in different microenvironments in Beijing, China, and implications for human exposure.

In the present study, the temporal distribution of PM-bound organophosphate flame retardants (OPFRs) was comprehensively investigated in various indoor environments as well as outdoor air in Beijing, China over a one-year period. The mean concentrations of ΣOPFRs were 22.7 ng m and 1.40 ng m in paired indoor and outdoor PM, respectively. The concentrations of tri-n-butyl phosphate (TNBP), tris (2-chloroethyl) phosphate (TCEP) and tris (2-chloroisopropyl) phosphate (TCIPP) in indoor PM were significantly correlated with those in outdoor PM. For different indoor microenvironments, mean concentrations of ΣOPFRs were in the order of office (29.0 ± 11.7 ng m) > home (24.0 ± 9.4 ng m) > dormitory (19.4 ± 4.9 ng m) > activity room (14.4 ± 3.1 ng m). TCIPP was the most abundant compound in the indoor PM, followed by TCEP. Significantly higher concentrations of OPFRs were observed in indoor environments with more furnishing, electronics or other materials (p < 0.05). Moreover, lower levels of OPFRs in indoor air were observed at well-ventilated (with higher air exchange rate) indoor sampling sites. Concentrations of ΣOPFRs in the activity room, dormitory, homes and outdoor sites generally increased in summer and heating seasons (November 2016 to February 2017). Significant correlations (p < 0.05) were observed between temperatures and mass concentrations of OPFRs with higher vapor pressures, i.e. TNBP, TCEP and TCIPP in all indoor and outdoor samples. Seasonal differences in human exposure were observed and the highest daily exposure dose occurred in summer. Toddlers may suffer the highest exposure risk of PM-bound OPFRs via inhalation among all age groups. This is one of the very few studies that have revealed the seasonal variation and human exposure of PM-bound OPFRs in different microenvironments, which shed light on emission sources and fate of OPFRs and potential human exposure pathway.