Atmospheric deposition and co-occurrence patterns of organophosphate flame retardants (OPFRs) and perfluorooctanoic acid (PFOA) in urban snow

Atmospheric deposition represents an important pathway for the transfer of emerging contaminants to terrestrial and aquatic environments, yet data on organophosphate flame retardants (OPFRs) remain scarce. In this study, the occurrence, concentration levels, and co-occurrence of eight OPFRs and per- and polyfluoroalkyl substances (PFAS) were investigated in urban snow samples collected during February 2025. A total of fifteen composite samples were obtained from thirteen locations in Bucharest and Ilfov County and two sites in Ramnicu Valcea, Romania, reflecting contrasting urban and regional atmospheric settings. A total of eight OPFRs and 27 PFAS were targeted using LC-MS/MS analysis. Among OPFRs, tris(1-chloro-2-propyl) phosphate (TCPP) was the dominant compound, with concentrations ranging from 43.4 to 691 ng/L (mean 188 ng/L), accounting for the largest contribution to ΣOPFRs (2818 ng/L). Moderate levels were observed for the other OPFR compounds, except bis(2-ethylhexyl) phosphate (BEHP), which showed sporadic occurrence, and both dibutyl phosphate (DBP) and triphenyl phosphate (TPP), which were consistently below the limit of quantitation of the analytical method. The total OPFRs burden exhibited substantial spatial variability, reflecting differences in emission sources and atmospheric transport conditions. Among the 27 PFAS analyzed, only perfluorooctanoic acid (PFOA) was detected above the method quantitation limit, with concentrations between 12.3 and 38.7 ng/L (mean: 26.0 ng/L), indicating a distinct behaviour compared to OPFRs. The co-occurrence of OPFRs and PFOA in snow highlights the role of atmospheric deposition as a relevant pathway for the simultaneous input of diverse anthropogenic contaminants into urban ecosystems.