Soil-bound 3,4-dichloroaniline: source of contamination in rice grain.

Abstract

Halogenated anilines (3,4-dichloroaniline or 3-chloroaniline) have been detected in all tested market rice samples (STILL and MANSAGER 1969). The parent compounds of these residues were assumed to be the herbicides employed on the respective fields. The herbicide propanil (3,4-dichloropropionanilide) is a selective herbicide for weed control in rice fields (SMITH 1961). In soil and plants, especially rice plants, propanil is rapidly hydrolyzed to propionic acid and 3,4-dichloroanillne (DCA) (BARTHA and PRAMER 1970, STILL and KUEIRIAN 1967). The former is completely degraded while most of the DCA persists in form of soilbound residues (BARTHA 1971, HSU and BART}IA 1974a). The pesticide is usually applied to rice fields when plants are very young; therefore, the aniline appearing in rice grains must have originated from soil and/or plant storage sites. We thought it important to determine the source of this contaminant of market rice and wish to report here the results of some studies on the mobility of persistent anilines using radiolabeled DCA applied to soil and to leaves of developing rice plants. EXPERIMENTAL Soil. The soil employed in these experiments was obtained through the courtesy of R. J. Smith, U.S.D.A., and originated from a rice field in Arkansas. To improve its texture, the soll was mixed with sand at a soil/sand ratio of 1:3 and filled to 2.5 cm from the top of nine 23 cm x 23 cm porcelain pots (side draining). The pots were watered and additional soil added So that all nine pots contained the same volume. Rice Plants. All plants were maintained in the greenhouse for a 28-week period (December 16 to July 9). Untreated rice seed (Oryza sativa var. Starbonnet) was obtained from the Jacob Hartz Seed Co., Stutgart, Arkansas, and was germinated in vermiculite. Watered with a routine greenhouse nutrient solution, seedlings were allowed to develop to the 3-4 leaf stage. Plants at the 4-1ear stage were then selected and transplanted to the soil/