Organophosphate Esters in Air and Seawater of the South China Sea: Spatial Distribution, Transport, and Air-Sea Exchange.

Organophosphate esters (OPEs) have become one group of chemicals with emerging concern in the marine environment. In this work, we investigated OPEs in the air and seawater of the South China Sea in summer 2019. The concentrations of ∑OPEs in the atmosphere ranged from 66 to 550 pg/m, with TCIPP, TNBP, TPhP, and TEP predominating in the air. The total dissolved OPE concentrations (∑OPEs without TEP) measured in high-volume water samples ranged from 300 to 3600 pg/L, with a mean concentration of 1180 ± 910 pg/L. TEP was measured with liquid-liquid extraction (LLE), and it showed the highest concentration (average 2000 ± 1450 pg/L) among the selected OPEs. Total suspended matter associated OPEs accounted for less than 4.7% of the sum of OPE concentrations in seawater. Fugacity fractions and air-sea exchange fluxes showed that TCEP, TCIPP, TIBP, TEHP, TPhP, and EHDPP were favored to volatilize, TEP dominated the deposition, while TPrP and TNBP varied between volatilization and deposition. Atmospheric particle deposition fluxes ranged from 5 to 71 ng/m/day with an average of 17 ± 15 ng/m/day. The input of ∑OPEs to the entire South China Sea via atmospheric particle deposition was estimated to be 22 ± 19 tons/year, while the net air-sea exchange fluxes of OPEs were volatilization from seawater to air with an average of 44 ± 33 tons/year. This work suggests that air-sea exchange and atmospheric particle deposition are significant processes interfering with the transport of OPEs in the marine environment.