Full Description

This study presents kinetics and degradation pathways for the reactions between sodiumhypochlorite (free available chlorine - FAC) or chloramines (combined chlorine - CC) and substratecompounds representative of three commonly prescribed and environmentally prevalent classes ofantibiotics: fluoroquinolones, sulfonamides, and dihydrofolate reductase (DHFR) inhibitors. Pseudo-first-orderkinetics was observed for oxidation of the fluoroquinolone antibiotic enrofloxacin (EF),sulfonamide antibiotic sulfamethoxazole (SMX), and DHFR inhibitor trimethoprim (TMP) by FAC.Second-order rate constants for reactions involving EF, SMX, and TMP were calculated from observedpseudo-first-order constants, on the assumption that concentration of oxidant remained essentiallyconstant throughout the monitoring periods of each kinetic experiment. Solution pH exhibited a markedinfluence on reaction rates for all three antibiotic classes. Consideration of predominant antibiotic speciesand corresponding reaction rates at specific pH values allowed a preliminary determination of reactivesites within the antibiotics. Compounds representing the hypothesized reactive and non-reactive portionsof each antibiotic class were utilized to verify the proposed location(s) of reactivity. LC/MS and H1-NMRwere used where applicable to identify reaction products and to assess product evolution during eachreaction time course. Product characterization of CF reaction mixtures indicates the formation of anumber of products, represented primarily by four major degradates corresponding to m/z 263, 297, 306,and 340 (corresponding to full or partial dealkylation of the piperazine ring and, in two cases,substitution of Cl on the quinolone structure's aromatic ring). The relatively rapid oxidation of SMX isaccompanied by what appears to be a unique radical-chain cleavage of the S-N sulfonamide bond to yield3-amino-5-methylisoxazole and an unknown product. S-N bond cleavage, combined with N-chlorinationof the aniline functional group, also appears to lead to the formation of relatively stable dimers and anumber of lower mass products. Chlorination of TMP yields primarily stable, multiply-halogenatedproducts, with the parent compound undergoing relatively minor structural modification. The results ofthis investigation indicate that representative members of these three antibiotic classes are substantiallydegraded under conditions simulating chlorination of water supplies during disinfection processes,yielding a wide variety of lower and higher mass degradates. Includes 32 references, figures.

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Edition: Vol. - No. Published: 11/02/2003 Number of Pages: 10File Size: 1 file , 340 KB