Although the bioaccumulation of organophosphate flame retardants (OPFRs) in aquatic organisms has been investigated, little information is available about their bioaccumulation in mammals following chronic inhalation exposure. To address this knowledge gap, C57BL/6 mice were exposed to 7 PM 2.5 -associated OPFRs via the trachea to study their bioaccumulation, tissue distribution, and urinary metabolites. Low (corresponding to the real PM 2.5 concentrations occurring during winter in Guangzhou), medium, and high dosages were examined. After 72 days' exposure, ∑OPFR concentrations in tissues from mice in the medium dosage group decreased in the order of intestine > heart > stomach > testis > kidney > spleen > brain > liver > lung > muscle. Of the OPFRs detected in all three exposure groups, chlorinated alkyl OPFRs were most heavily accumulated in mice. We found a significant positive correlation between the bioaccumulation ratio and octanol−air partition coefficient (K OA ) in mice tissues for low log K OW OPFR congeners (log K OW ≤ 4, p < 0.05). Three urinary metabolites (di-p-cresyl phosphate: DCrP, diphenyl phosphate: DPhP, dibutyl phosphate: DnBP) were detected from the high dosage group. These results provide important insights into the bioaccumulation potential of OPFRs in mammals and emphasize the health risk of chlorinated alkyl OPFRs.

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The COVID-19 pandemic has raised awareness about various environmental issues, including PM 2.5 pollution. Here, PM 2.5 pollution during the COVID-19 lockdown was traced and analyzed to clarify the sources and factors influencing PM 2.5 in Guangzhou, with an emphasis on heavy pollution. The lockdown led to large reductions in industrial and traffic emissions, which significantly reduced PM 2.5 concentrations in Guangzhou. Interestingly, the trend of PM 2.5 concentrations was not consistent with traffic and industrial emissions, as minimum concentrations were observed in the fourth period (3/01-3/31, 22.45 μg•m −3 ) of the lockdown. However, the concentrations of other gaseous pollutants, e.g., SO 2 , NO 2 and CO, were correlated with industrial and traffic emissions, and the lowest values were noticed in the second period (1/24-2/03) of the lockdown. Meteorological correlation analysis revealed that the decreased PM 2.5 concentrations during COVID-19 can be mainly attributed to decreased industrial and traffic emissions rather than meteorological conditions. When meteorological factors were included in the PM 2.5 composition and backward trajectory analyses, we found that long-distance transportation and secondary pollution offset the reduction of primary emissions in the second and third stages of the pandemic. Notably, industrial PM 2.5 emissions from western, southern and southeastern Guangzhou play an important role in the formation of heavy pollution events. Our results not only verify the importance of controlling traffic and industrial emissions, but also provide targets for further improvements in PM 2.5 pollution.