Phototransformation of pesticides in prairie potholes: effect of dissolved organic matter in triplet-induced oxidation

Abstract

Photochemical reactions involving a variety of photosensitizers contribute to the abiotic transformation of pesticides in prairie pothole lakes (PPLs). Despite the fact that triplet excited state dissolved organic matter (DOM) enhances phototransformation of pesticides by acting as a photosensitizer, it may also decrease the overall phototransformation rate through various mechanisms. In this study, the effect of DOM on the phototransformation of four commonly applied pesticides in four different PPL waters was investigated under simulated sunlight using photoexcited benzophenone-4-carboxylate as the oxidant with DOM serving as an anti-oxidant. For atrazine and mesotrione, a decrease in phototransformation rates was observed, while phototransformations of metolachlor and isoproturon were not affected by DOM inhibition. Phototransformation rates and the extent of inhibition/enhancement by DOM varied spatially and temporally across the wetlands studied. Characterization of DOM from the sites and different seasons suggested that the DOM type and variations in the DOM structure are important factors controlling phototransformation rates of pesticides in PPLs.

Triplet state dissolved organic matter in aquatic photochemistry: reaction mechanisms, substrate scope, and photophysical properties

“…Ground-state reduction potentials (E ), triplet energies (E T ), triplet state reduction potentials (E *), and singlet oxygen quantum yields (F D ) for selected DOM model sensitizers and other widely used sensitizers Entry 68 but also more complex structures, such as found in phenylurea herbicides, 28,69-72 sulfa drugs, 45,46,[73][74][75] chloroacetamide herbicides, 28,72 diarylamines (e.g., mefenamic acid 44 ), and arguably within the structure of tryptophan 47,76 and indole 77 (Fig. 4).…”

Photochemical fate of quaternary ammonium compounds in river water

“…6,46 Direct photolysis occurs when a contaminant undergoes transformation, such as breaking of bonds, resulting from directly absorbing light energy. 47 Many QACs lack chromophoric functional groups or exhibit poor absorption of light in the visible spectrum; thus, direct photolysis processes may be limited in natural waters. Indirect photolysis, facilitated by QAC association with dissolved organic matter (DOM), could be an important and understudied attenuation mechanism.…”

“…Indirect photolysis occurs when a photosensitizer such as organic matter in natural waters absorbs light energy, becomes electronically excited, and subsequently reacts with a contaminant or produces transient photochemically produced reactive intermediates (PPRIs) that are energetically capable of transforming target contaminants. 47 PPRIs, including reactive oxygen species (ROS), such as hydroxyl radicals (cOH) and singlet oxygen ( 1 O 2 ), and non-ROS excited triplet states of DOM ( 3 DOM*), react with contaminants in natural systems thus enhancing degradation and increasing phototransformation rates. [47][48][49][50] QACs may sorb to DOM, which is ubiquitous in natural waters, and this interaction affects their distribution, transformation, and bioavailability.…”

“…47 PPRIs, including reactive oxygen species (ROS), such as hydroxyl radicals (cOH) and singlet oxygen ( 1 O 2 ), and non-ROS excited triplet states of DOM ( 3 DOM*), react with contaminants in natural systems thus enhancing degradation and increasing phototransformation rates. [47][48][49][50] QACs may sorb to DOM, which is ubiquitous in natural waters, and this interaction affects their distribution, transformation, and bioavailability. In aquatic systems, DOM may act as a sink for QACs and as a photosensitizer.…”

Electrochemical characterization of natural organic matter by direct voltammetry in an aprotic solvent

“…40,[45][46][47][48][49][50][51] The other major applications of NOM characterization are to its role in biogeochemistry, 46,[52][53][54][55][56] and contaminant fate. [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73] In both of these contexts, NOM participates in reactions as a ligand, [74][75][76][77][78] electron donor/acceptor, 53,56,[79][80][81][82][83][84][85][86][87] electron shuttle (i.e., electron-transfer mediator), [88][89][90]…”