1f:T4ac,Sorption interactions of three high-use tetracycline antibiotics (oxytetracycline, chlortetracycline, tetracycline) with montmorillonite and kaolinite clays were investigated undervaried pH and ionic strength conditions. Sorption edges were best described with a model that included cation exchange plus surface complexation of zwitterion forms of these compounds. Zwitterion sorption was accompanied by proton uptake, was more favorable on acidic clay, and was relatively insensitive to ionic strength effects. Calcium salts promoted oxytetracycline sorption at alkaline pHs likely by a surface-bridging mechanism. Substituent effects among the compounds in the tetracycline class had only minor effects on sorption edges and isotherms under the same solution pH and ionic strength conditions. At low ionic strength, greater sorption to montmorillonite than kaolinite was observed at all pHs tested, even after normalizing for cation exchange capacity. These results indicate that soil and sediment sorption models for tetracyclines, and other pharmaceuticals with similar chemistry, must account for solution speciation and the presence of other competitor ions in soil or sediment pore waters.20:T51e,Different dissolved natural organic materials photosensitize the transformation of a series of methyl and methoxy phenols at pH 8 with a very similar high selectivity (reactivity range ≈50). This selectivity falls in the range of that achieved using the aromatic ketones benzophenone (BP), 3′-methoxyacetophenone (3′-MAP), and 2-acetonaphthone (2-AN) as model photosensitizers. For both natural and model sensitizers, the photooxidation at pH 8 is not controlled by singlet oxygen. Deuterium isotope effects (k_H/k_D) of different phenols are 0.7-1.3 for humic and fulvic acids and 1.1-1.7 for BP, suggesting an electron transfer mechanism. In contrast, the isotope effect for 2-AN of ≈4 indicates an H-atom abstraction reaction. The results show that reactive excited triplet states are important photooxidants in natural waters and should be considered for assessing the abiotic degradation of chemicals. The reactive triplet state concentration is estimated to be ≈10^-14 M in the top meter of Lake Greifensee under summer noon sunlight, and this leads to a half-life of ≈7 h for 2,4,6-trimethylphenol. Further still uncharacterized photooxidants derived from the dissolved organic material are also involved in the phototransformation of the phenols.21:T676,

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