Formation and reactivity of the dichloride radical (Cl2–•) in surfacewaters: A modelling approach

The occurrence of Cl-2(-) in natural waters would depend on the budget between triplet-sensitised photogeneration (which might have second-order rate constant of 10(7)-10(9) M-1 s(-1)) and scavenging by dissolved organic matter (DOM, with possible rate constant of 10-10(3) L (mg C)(-1) s(-1)). The steady-state [Cl-2(-)] in brackish to saline waters might be in the range of 10(-14)-10(-12) M in mid-latitude summertime, coherently with data of phenol photochlorination in seawater. Steady-state [Cl-2(-)] would be enhanced by chloride (up to a plateau above 0.1 M Cl-) and inhibited by DOM. The radical Cl-2(-) would also be a major oxidant of nitrite to the nitrating agent.NO2 in brackish- and salt-water. This issue may explain the sustained formation of nitrophenols in phenol-spiked seawater and in natural brackish waters impacted by phenolic pollutants (Rhone delta, Southern France).