Enrichment of Organophosphate Esters in the Sea Surface Microlayer from the Atlantic and Southern Oceans

The sea surface microlayer (SML) is the thin interface between the ocean and the atmosphere, exhibiting an enrichment of hydrophobic and surfactant-like chemicals. Here we report the concentrations of organophosphate esters (OPEs), widely used flame retardants and plasticizers, in the SML and underlying waters from a north–south transect in the Atlantic and Southern Oceans. Generally, concentrations of OPEs in the SML were higher than in the underlying waters. Concentrations in the SML were correlated with the chlorophyll α content for some OPEs, consistent with biogenic surfactants at the SML. The enrichment factors (ratio of concentrations in SML over concentrations in underlying waters) were 5.84 ± 8.97 and 9.10 ± 9.48 for the Atlantic and Southern Oceans, respectively. The average enrichment factors in sea spray aerosols (SSA), estimated using previously reported aerosol-phase concentrations, ranged from 3.69 × 10⁴ to 3.33 × 10⁶. These OPE enrichments in SSA are high and suggest that the formation of SSA, mediated by the enrichment in the SML, could be relevant for many semivolatile organic pollutants. Future research is needed to elucidate the variables driving the enrichment in the SML, its large variability, as well as its role in the fate of organic pollutants.