COMPARISON OF FORMATION AND BIODEGRADATION OF BROMACIL OXIDATION-PRODUCTS IN AQUEOUS-SOLUTIONS

A comparative study of several oxidation methods of aqueous bromacil ( I) solutions was conducted as part of a series of investigations conce rning the chemical and biological remediation of pesticide-laden waste s. Ozonation (A), UV photolysis at 254 nn (B), and sensitized sunlight photodegradation (C) methods were examined. The A products were isola ted and their structures elucidated by mass spectroscopy, various C-13 and H-1 NMR techniques, and other chemical methods. Three main A prod ucts were identified: 3-sec-butyl-5-acetyl-5-hydroxyhydantoin (II, ca. 5%), 3-sec-butylparabanic acid (III, ca. 20%), and 3-sec-butyl-5,5-di bromo-6-methyl-6-hydroxyuracil (IV, ca. 5%), which was also synthesize d via hydroxybromination of bromacil; a fourth product (VII) was obtai ned in minute amount but was not identified. The aqueous solutions of IV are unstable and its decomposition led to re-formation of I. The ma in products found in B [(3-sec-butyl-6-methyluracil (V) and a dimer co mpound, VI] and C (II and VI) were similar to those described previous ly. The biodegradation assays of I, A, B, and C solutions were investi gated using activated sludge, a pure culture of Klebsiella terragena ( DRS-I), or soil; they indicated that the B and C solutions were more b iodegradable than A solutions, while the parent material (I) was nonbi odegradable. A phytotoxicity bioassay, using Nicotiana tabacum seedlin gs, showed complete detoxification of the B and C solutions but only p artial detoxification of the A and IV solutions. An attempt has been m ade to evaluate the most suitable method of degradation of solutions o f I.