This study investigates the oxidation of pharmaceuticals during conventional ozonation and advanced oxidation processes (AOPs) applied in drinking water treatment. In a first step, second-order rate constants for the reactions of selected pharmaceuticals with ozone (k(O3)) and OH radicals (k(OH)) were determined in bench-scale experiments (in brackets apparent k(O3) at pH 7 and T = 20 degrees C): bezafibrate (590 +/- 50 M(-1) s(-1)), carbamazepine (approximately 3 x 10(5) M(-1) s(-1)), diazepam (0.75 +/- 0.15 M(-1) s(-1)), diclofenac (approximately 1 x 10(6) M(-1) s(-1)), 17alpha-ethinylestradiol (approximately 3 x 10(6) M(-1) s(-1)), ibuprofen (9.6 +/- 1.0 M(-1) s(-1)), iopromide (<0.8 M(-1) s(-1)), sulfamethoxazole (approximately 2.5 x 10(6) M(-1) s(-1)), and roxithromycin (approximately 7 x 10(4) M(-1) s(-1)). For five of the pharmaceuticals the apparent k(O3) at pH 7 was >5 x 10(4) M(-1) s(-1), indicating that these compounds are completely transformed during ozonation processes. Values for k(OH) ranged from 3.3 to 9.8 x 10(9) M(-1) s(-1). Compared to other important micropollutants such as MTBE and atrazine, the selected pharmaceuticals reacted about two to three times faster with OH radicals. In the second part of the study, oxidation kinetics of the selected pharmaceuticals were investigated in ozonation experiments performed in different natural waters. It could be shown that the second-order rate constants determined in pure aqueous solution could be applied to predict the behavior of pharmaceuticals dissolved in natural waters. Overall it can be concluded that ozonation and AOPs are promising processes for an efficient removal of pharmaceuticals in drinking waters.

Excited triplet states of chromophoric dissolved organic matter (CDOM*) play a major role among the reactive intermediates produced upon absorption of sunlight by surface waters. After more than two decades of research on the aquatic photochemistry of CDOM*, the need for improving the knowledge about the photophysical and photochemical properties of these elusive reactive species remains considerable. This critical review examines the efforts to date to characterizeCDOM*. Information on CDOM* relies mainly on the use of probe compounds because of the difficulties associated with directly observingCDOM* using transient spectroscopic methods. Singlet molecular oxygen (O), which is a product of the reaction between CDOM* and dissolved oxygen, is probably the simplest indicator that can be used to estimate steady-state concentrations ofCDOM*. There are two major modes of reaction of CDOM* with substrates, namely triplet energy transfer or oxidation (via electron transfer, proton-coupled electron transfer or related mechanisms). Organic molecules, including several environmental contaminants, that are susceptible to degradation by these two different reaction modes are reviewed. It is proposed that through the use of appropriate sets of probe compounds and model photosensitizers an improved estimation of the distribution of triplet energies and one-electron reduction potentials ofCDOM* can be achieved.

The benefits of global pesticide use come at the cost of their widespread occurrence in the environment. An array of abiotic and biotic transformations effectively removes pesticides from the environment, but may give rise to potentially hazardous transformation products. Despite a large body of pesticide degradation data from regulatory testing and decades of pesticide research, it remains difficult to anticipate the extent and pathways of pesticide degradation under specific field conditions. Here, we review the major scientific challenges in doing so and discuss emerging opportunities to identify pesticide degradation processes in the field.

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Aromatic ketones efficiently mediate the photo-oxidative degradation of phenols in aerated aqueous solution, a process likely to be relevant in sunlit natural waters. Absolute bimolecular rate constants for the quenching of three model ketone triplets by nine phenols bearing various substituents, from electron-donating alkyl and alkoxy groups to the electron-withdrawing cyano group, were measured by nanosecond laser flash photolysis. Triplet benzophenone (BP) is quenched at nearly diffusion-controlled rates (2.6−5.6 × 109 M-1 s-1). Triplet state quenching of 3‘-methoxyacetophenone (3‘-MAP) and 2-acetonaphthone (2-AN) by the same set of phenols occurs more selectively, with rate constants spanning a range of 1 and more than 2 orders of magnitude, respectively. Quenching rate constants obey a Rehm−Weller relationship to the free energy of electron transfer from the phenol to the ketone triplet. By comparison of the quenching constants with overall photo-oxidation rates obtained by stationary irradiation in air-saturated aqueous solution, phenols bearing electron-donating substituents were found to be depleted with quantum yields generally exceeding 0.5, whereas parent phenol and, presumably, acceptor-substituded phenols are transformed at only ∼0.1 efficiency. The present quenching data were used to interpret the efficiency of photosensitized oxidation of phenols by dissolved natural organic matter (DNOM), an important sunlight absorber present in surface waters. The effective reduction potential of reactive excited triplet states in DNOM was estimated to be at least 1.36 V vs NHE.