Photochemical Degradation of Diuron and Monuron

Abstract

(ONSIDERABLE attention has been given during recent years to the . fate of herbicides sprayed onto soil surfaces. The effect of light upon herbicides also has been studied extensively. Payne and Fults by means of a biological test found that the potency of 2,4-D was increased by exposure to ultraviolet light (7). Hansen and Buchholtz found that when a solution containing 2,4-D and riboflavin was exposed to light the activity of 2,4-D was reduced (5). They tentatively identified the breakdown product as 2,4-dichlorophenol. Later Bell positively identified it (1). Hill et al. found that 83 percent of the 3-(p--chlorophenyl)-l,1dimethylurea (monuron) was lost when exposed to sunlight for 48 days (6). Birk found that photodecomposition was a factor in the disappearance of monuron (2). Woodford concluded that photodecomposition is of practical importance only in areas where little rain occurs and the herbicides remain on the soil surface for prolonged periods (9). It was shown by Dorschner and Buchholtz and others that spectrophotometric analysis of herbicides is a rapid quantitative technique (3). 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron) is used in Wyoming for the control of annual weeds in alfalfa (8). The applications are made in the spring, and often precipitation does not occur for several weeks. Because of the absence of moisture including dew, there are optimum conditions for photochemical reactions. The objectives of the experiment were to determine (1) the effect of a controlled light source upon monuron and diuron and (2) the biological activity of any changed material.