Effect of Dissolved Organic Matter on the Transformation of Contaminants Induced by Excited Triplet States and the Hydroxyl Radical

Abstract

Dissolved organic matter (DOM) has recently been shown to reduce the transformation rate of various aqueous organic contaminants submitted to oxidation by excited triplet states, apparently by inhibiting the transformation of oxidation intermediates. The main goals of the present study were to evaluate in more detail the effect of concentration and type of DOM on the triplet-induced transformation rate of four selected organic compounds and to check for an analogous inhibition effect in the case of oxidation induced by hydroxyl radical. A marked inhibition by DOM of triplet-induced oxidation was observed for N,N-dimethylaniline (DMA) and the two antibiotics sulfamethoxazole (SMX) and trimethoprim (TRI), with DOM of terrestrial origin being a more effective inhibitor than DOM of aquatic origin. The results are important to understand the role of DOM both as a photosensitizer and as an inhibitor for the triplet-induced transformation of aquatic contaminants. In contrast, no DOM-induced reduction in second-order rate constant could be observed in competition kinetics experiments for the reaction of hydroxyl radical with a series of 15 organic compounds, covering several classes of aromatic contaminants, indicating that Suwannee River fulvic acid (SRFA) used as reference DOM does not affect this reaction mechanism.

Mechanism, kinetics and toxicity assessment of OH-initiated transformation of triclosan in aquatic environments

“…Research in this area has mainly been focused on identifying and quantifying the polychlorinated dibenzo-p-dioxin (called "dioxin" in the rest of this paper) photoproducts that can be formed and the transformation pathways in the direct photolysis and photosensitized transformation of TCS (Anger et al, 2013;Kliegman et al, 2013;Latch et al, 2003Latch et al, , 2005Mezcua et al, 2004;WongWah-Chung et al, 2007 formed and are constantly present at low concentrations in natural waters (Dong and Rosario-Ortiz, 2012;Vione et al, 2006). Of these, OH is a well-known highly reactive oxidant that plays an important role in the transformation of a wide spectrum of ECs in natural waters (Dong and Rosario-Ortiz, 2012;Wenk et al, 2011) because of the high absolute bimolecular rate constants with ECs (An et al, 2010a(An et al, , 2010bBuxton et al, 1988;Fang et al, 2013;Yang et al, 2010). High OH concentrations can be produced easily under certain extreme conditions, for example in advanced oxidation process (AOP) systems (An et al, 2010a(An et al, , 2010bBokare and Choi, 2011;Fang et al, 2013;Shu et al, 2013;Yang et al, 2010).…”

Rapid solid phase extraction of dissolved organic matter

“…Nutrients (P, N, and trace metals) often occur in organic form and thus dissolved organic matter plays an important role in carbon and nutrient cycles from local to global scales (Mopper et al 1991;Hedges 1992;Jiao et al 2010). Natural DOM acts as a "sunscreen" altering visible light availability for photosynthesis and the penetration of harmful UV radiation (Mopper and Kieber 2002); it also acts as a photosensitizer/photoinhibiter for other chemical species (Miller and Chin 2005;Wenk et al 2011;Zeng and Arnold 2013). DOM's efficacy in these roles depends upon its molecular-level composition, which is variable both spatially and temporally as a result of varied sources (Minor and Stephens 2008), photobleaching (Mopper et al 1991;Dalzell et al 2009;Minor et al 2007;Stephens and Minor 2010), and microbial degradation (Obernosterer and Benner 2004).…”

Direct and indirect photolysis of triclocarban in the presence of dissolved organic matter

“…In contrast those compounds that are susceptible to oxidation by 3 DOM react more readily with organic matter derived from autochthonous sources i.e., from phytoplankton and other microorganisms. Research by Wenk et al (2011Wenk et al ( , 2012 has demonstrated that the presence of anti-oxidants such as phenolic compounds in allochthonous DOM is responsible for this disparity. The presence of these anti-oxidants could result in the reversion of meta-stable photo-intermediates back to the parent compound, which is manifested as "slower" reaction kinetics.…”

“…In our previous studies we demonstrated that allochthonous DOM is effective at generating ROS such as the hydroxyl radical (OH•), while autochthonous organic matter is effective at forming 3 DOM (Guerard et al, 2009;Cawley et al, 2009). Subsequent research by Wenk et al (2011Wenk et al ( , 2012 demonstrated that the presence of unknown anti-oxidant moieties (presumably phenolic compounds) present in allochthonous DOM (and much less prevalent in autochthonous DOM) maybe responsible for this dichotomy in DOM photo-reactivity. These investigators postulated that anti-oxidants prevent the oxidation of aniline contaminants by 3 DOM by reverting the analyte intermediate back to the parent compound.…”