Singlet Oxygen Photogeneration in Coastal Seawater: Prospect of Large-Scale Modeling in Seawater Surface and Its Environmental Significance.

Chromophoric-dissolved organic matter (CDOM) acts as the precursor to singlet oxygen (O) in natural waters, while water acts as the main scavenger. In this study, we showed that O in coastal seawater can be successfully predicted from CDOM parameters. The O steady-state concentration [O] and photoformation rate (O) varied by a factor of 6 across 13 sampling stations in the Seto Inland Sea, Japan, ranging from 1.2 to 8.2 × 10 M and 3.32 to 22.7 × 10 M s, respectively. Investigation of CDOM optical properties revealed that CDOM abundance measured as the absorption coefficient at 300 nm () had the strongest correlation ( = 0.96, < 0.001) with [O], while parameters indicative of CDOM quality (e.g., spectral slope) did not influence [O]. A linear relationship between [O] and , normalized to a sunlight intensity of 0.91 kW/m, was derived as [O] (10 M) = 2.12() + 0.48. This was then used to predict [O] using values from a subsequent, independent sampling exercise conducted 2 years after the first sampling. There was a good agreement ( = 0.93, < 0.001) between the predicted values and the experimentally determined values based on a 95% prediction interval plot. Kinetic estimations using [O] suggest that O mediates the degradation of tetrabromobisphenol A in surface seawater ( = 0.63 days) while also contributing to the indirect photolysis of methyl mercury. The findings from this study suggest that large-scale modeling of O generation in surface seawater from CDOM parameters is possible with useful environmental significance for determining the fate of pollutants.