Leaching of Rice Herbicide, Cyhalofop-Butyl in Vertisols Following an Application in Lysimeters under Tropical Rainfall Conditions

Abstract

Leaching can significantly contribute to pesticide contamination of surface and ground water. Therefore, leaching of a rice herbicide, cyhalofop-butyl, i.e., (butyl(R)-2-[4-cyano-2-fluorophenoxy)phenoxy])propanoate was examined in sandy loam soil in field lysimeters at two levels of applications. A quantitative evaluation of soil samples taken at 0-225 cm depths indicated that rainfall events in initial days caused leaching of cyhalofop-butyl and an amount of 0.48 and 0.104 μg L^-1 cyhalofop-butyl were detected in the leachates in corresponding to two application levels. After receiving 253.2 mm of rainfall average concentration of cyhalofop-butyl at 0-100 cm soil depths at two levels of application was found 78.7 to 19.16 % which was decreased to 5.58, 5.37 % after receiving 91.9 and 15.2 mm rainfall at 5 and 10th day, respectively. Rapid degradation of cyhalofop-butyl occurred in the soil at various depths though the chemical hydrolysis process and three degradation products of cyhalofop-butyl were detected from soil and leachates. The study showed that measured concentration of cyhalofop-butyl did not exceed EPA guidelines values of no observed effect level (NOEL) on aquatic system in the water.