Photo-production of excited triplet-state of dissolved organic matters in inland freshwater and coastal seawater

The excited triplet-state of dissolved organic matter ((DOM)-D-3*) is a major reactive intermediate in sunlit waters. Its quantum yield is important in understanding the fate of organic micropollutants. The degradation efficiency of its chemical probe, 2,4,6-trimeythlphenol (f(TMP)), is generally used as a proxy of the quantum yield. However, f(TMP) has been described and modelled only for freshwater systems. Therefore, this study quantified f(TMP) in inland freshwater and coastal seawater sampled in Japan by conducting steady-state photochemical experiments. Optical properties of water were then used to model f(TMP). Results indicated that the inland freshwater DOM originated mainly from terrestrial sources, while the coastal seawater DOM were microbial-dominated. On average, inland freshwater exhibited lower f(TMP) (61.2 M-1) than coastal seawater (79.7 M-1) and the coastal seawater exhibited significant variations in the proportion of high-energy (DOM)-D-3* (> 250 kJ/mol). In addition, E-2:E-3 (ratio of absorbance at 254 to 365 nm) was positively correlated with f(TMP) of inland freshwater, coastal seawater, and the overall dataset. Catchment conditions such as forest coverage also influenced the production of (DOM)-D-3* and high-energy (DOM)-D-3* in inland freshwater. Furthermore, the developed models estimated f(TMP) based on the optical properties of both freshwater and seawater, providing valuable insights about (DOM)-D-3* photochemistry in the aquatic environment.