The occurrence of View the MathML sourceCl2- in natural waters would depend on the budget between triplet-sensitised photogeneration (which might have second-order rate constant of 107-109 M−1 s−1) and scavenging by dissolved organic matter (DOM, with possible rate constant of 10-103 L (mg C)−1 s−1). The steady-state [View the MathML sourceCl2-] 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 [View the MathML sourceCl2-] would be enhanced by chloride (up to a plateau above 0.1 M Cl−) and inhibited by DOM. The radical View the MathML sourceCl2- would also be a major oxidant of nitrite to the nitrating agent radical dotNO2 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).