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 concerning the chemical and biological remediation of pesticide-laden wastes. Ozonation (A), UV photolysis at 254 nm (B), and sensitized sunlight photodegradation (C) methods were examined. The A products were isolated and their structures elucidated by mass spectroscopy, various ¹³C and ¹H NMR techniques, and other chemical methods. Three main A products 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-dibromo-6-methyl-6-hydroxyuracil (IV, ca. 5%), which was also synthesized via hydroxybromination of bromacil; a fourth product (VII) was obtained in minute amount but was not identified. The aqueous solutions of IV are unstable and its decomposition led to re-formation of I. The main products found in B [(3-sec-butyl-6-methyluracil (V) and a dimer compound, VI) and C (II and VI) were similar to those described previously. The biodegradation assays of I, A, B, and C solutions were investigated using activated sludge, a pure culture of Klebsiella terragena (DRS-I), or soil; they indicated that the B and C solutions were more biodegradable than A solutions, while the parent material (I) was nonbiodegradable. A phytotoxicity bioassay, using Nicotiana tabacum seedlings, showed complete detoxification of the B and C solutions but only partial detoxification of the A and IV solutions. An attempt has been made to evaluate the most suitable method of degradation of solutions of I.