Photochemical fate of carbamazepine in surface freshwaters: laboratory measures and modeling

It is shown here that carbamazepine (CBZ) would undergo direct photolysis and reaction with (•)OH as the main phototransformation pathways in surface waters. Environmental lifetimes are expected to vary from a few weeks to several months, and predictions are in good agreement with available field data. Acridine (I) and 10,11-dihydro-10,11-trans-dihydroxy-CBZ (V) are the main quantified phototransformation intermediates upon direct photolysis and (•)OH reaction, respectively. The photochemical yield of mutagenic I from CBZ is in the 3-3.5% range, and it is similar for both direct photolysis and (•)OH reaction: it would undergo limited variation with environmental conditions. In contrast, the yield of V would vary in the 4-8.5% range depending on the conditions, because V is formed from CBZ by (•)OH (9.0% yield) more effectively than upon direct photolysis (1.4% yield). Other important photointermediates, mostly formed from CBZ upon (•)OH reaction, are an aromatic-ring-dihydroxylated CBZ (VI) and N,N-bis(2-carboxyphenyl)urea (VII). Compounds VI and VII are formed by photochemistry and are not reported as human metabolites; thus, they could be used as tracers of CBZ phototransformation in surface waters. Interestingly, VI has recently been detected in river water.