posted on 2020-04-28, 12:34authored byMichael
O. Sunday, Kazuhiko Takeda, Hiroshi Sakugawa
Chromophoric-dissolved organic matter
(CDOM) acts as the precursor
to singlet oxygen (1O2) in natural waters, while
water acts as the main scavenger. In this study, we showed that 1O2 in coastal seawater can be successfully predicted
from CDOM parameters. The 1O2 steady-state concentration
[1O2]ss and photoformation rate (R1O2) varied by a factor of 6 across
13 sampling stations in the Seto Inland Sea, Japan, ranging from 1.2
to 8.2 × 10–14 M and 3.32 to 22.7 × 10–9 M s–1, respectively. Investigation
of CDOM optical properties revealed that CDOM abundance measured as
the absorption coefficient at 300 nm (a300) had the strongest correlation (r = 0.96, p < 0.001) with [1O2]ss, while parameters indicative of CDOM quality (e.g., spectral slope)
did not influence [1O2]ss. A linear
relationship between [1O2]ss and a300, normalized to a sunlight intensity of 0.91
kW/m2, was derived as [1O2]ss (10–14 M) = 2.12(a300) + 0.48. This was then used to predict [1O2]ss using a300 values from
a subsequent, independent sampling exercise conducted 2 years after
the first sampling. There was a good agreement (r = 0.93, p < 0.001) between the predicted values
and the experimentally determined values based on a 95% prediction
interval plot. Kinetic estimations using [1O2]ss suggest that 1O2 mediates the
degradation of tetrabromobisphenol A in surface seawater (t1/2 = 0.63 days) while also contributing to
the indirect photolysis of methyl mercury. The findings from this
study suggest that large-scale modeling of 1O2 generation in surface seawater from CDOM parameters is possible
with useful environmental significance for determining the fate of
pollutants.