Formation and reactivity of the dichloride radical (Cl2(-·)) in surface waters: a modelling approach.

The occurrence of Cl2(-·) 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 [Cl2(-·)] 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 [Cl2(-·)] would be enhanced by chloride (up to a plateau above 0.1 M Cl(-)) and inhibited by DOM. The radical Cl2(-·) 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 (Rhône delta, Southern France).