PROPANIL - TOXICOLOGICAL CHARACTERISTICS, METABOLISM, AND BIODEGRADATION POTENTIAL IN SOIL

Propanil [3',4'-dichloropropionanilide (DCPA)] is a biologically active pollutant. Propanil is extensively used around the world for control of weeds in rice (Oryza sativa L.) production. Although propanil by itself is of low toxicity, the highly toxic impurities 3,3',4,4'-tetrachloroazobenzene (TCAB) and 3,3',4,4'-tetrachloroazoxybenzene (TCAOB) from the manufacture of 3,4-dichloroaniline (DCA) often contaminate the 3,4-DCA-derived herbicide propanil. These compounds are approximately isosteric to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and acting at the Ah receptor, are toxic by mechanisms similar to those of TCDD. Both TCAB and TCAOB are cytotoxic, embryolethal, and teratogenic, and hence are classified as possible human genotoxins. In soil, biodegradation of propanil liberates DCA, which is converted by microbial peroxidases to TCAB and other azo products. The TCAB and TCAOB may accumulate in rice-growing soils, and leach into groundwater. The toxicity and fate of these compounds in the environment and the ability of microorganisms to detoxify them are discussed.