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Enrichment of organophosphate esters in the surface microlayer of a subtropical urban lake: Phase partitioning dynamics and air-water exchange implications
Summary
Scientists found that flame-retardant and plasticizer chemicals (called OPEs) build up at surprisingly high levels in the thin surface layer of an urban lake—sometimes hundreds of times more concentrated than in the water below. This matters because these chemicals are common in household products and have been linked to health concerns, and this "skin" of concentrated chemicals on water surfaces affects how much of them evaporate into the air we breathe versus staying in water, meaning current pollution models may be underestimating human exposure risks.
Organophosphate esters (OPEs), a class of extensively utilized halogenated flame retardants and plasticizers, have emerged as ubiquitous environmental contaminants and have been detected in multiple matrices, posing potential ecological risks. In this study, we firstly investigated the particle-dissolved phase partition and enrichment of nine OPE compounds in the surface microlayer (SML) of a subtropical urban lake, and further estimate their influence to the air-water exchange process. The concentrations of ∑9OPEs in the dissolved and particle phases of the lake SML were 187-2.36 × 103 ng/L (average: 1100 ± 697 ng/L) and 64.0-294 ng/L (average: 133 ± 62.9 ng/L), respectively. Consistent with the subsurface water (SSW) of the lake, tris (1-chloro-2-propyl) phosphate (TCPP) and tris (2-chloroethyl) phosphate (TCEP) were the predominant OPEs in the SML. The particle fractions (fp) of OPEs in the SML were significantly positively related with their logKow values (p < 0.05), suggesting that OPEs with greater hydrophobicity were more likely to distribute in the particle phase. Significant enrichment of OPEs was observed in both the dissolved and particle phases of the SML, with enrichment factors (EFs) ranging from 0.78 to 409 and from 0.11 to 24.0, respectively. More hydrophobic OPEs also prefer to be enriched in the particle phase of the SML. The comparison of fugacity fractions and exchange fluxes of OPEs between air-SML and air-SSW in the lake demonstrated that the enrichment of OPEs in the SML would alter their air-water exchange processes, highlighting the need to incorporate microlayer-induced concentration gradients into the environmental fate modeling of OPEs.