Aerobic biodegradation of chiral phenoxyalkanoic acid derivatives during incubations with activated sludge

The aerobic biodegradation of racemic mixtures of five chiral phenoxyalkano ic acids was studied according to a biodegradation test that was complement ed with enantiomer-specific analysis. Both enantiomers of (RS)-2-phenoxypro panoic acid, (RS)-2-(3-chlorophenoxy)propanoic acid, and (RS)-2-(4-chloroph enoxy)propanoic acid, were completely degraded within 25 days when aerobica lly incubated with activated sludge. During incubations of (RS)-2-phenoxypr opanoic acid, the (R) enantiomer was degraded before the (S) enantiomer, wh ereas during incubations of (RS)-2-(3-chlorophenoxy)propanoic acid the (S) enantiomer was preferentially degraded. The (R) enantiomer of (RS)-2-(2-chl orophenoxy)propanoic acid was removed after 24 days while only 30% of the ( S) enantiomer was degraded within 47 days of incubation. (RS)-2-(2,4,5-Tric hlorophenoxy)propanoic acid was the most persistent of all the racemic mixt ures tested. After 47 days, the concentration of the (S) enantiomer was nea rly unchanged, and the concentration of (R)-2-(2,4,5-trichlorophenoxy) prop anoic acid had decreased only by about 40%. The differences observed in the length of the lag phases and in the degradation rates of individual enanti omers can lead to accumulations of the more recalcitrant enantiomer in aqua tic or terrestrial ecosystems. (C) 1999 Federation of European Microbiologi cal Societies. Published by Elsevier Science B.V. All rights reserved.