Photo-oxidative degradation and quantification of herbicide residues for pesticidal pollution

Abstract

A highly selective and sensitive chromatographic technique in combination with electrochemical as well as photo-active detection has been developed to identify and determine trace levels of phenoxy herbicides, such as; 2,4-dichloro-phenoxyacetic acid (2,4-D); 2,4,5-trichloro-phenoxyacetic acid (2,4,5-T); 4-chloro-2-methylphenoxy acetic acid (MCPA); 2-(2,4-dichlorophenoxy) propionic acid (2,4-DP); 4-(2,4-dichlorophenoxy)butyric acid (MCPB) and 4-(3,4-dichlorophenoxy)butyric acid (2,4-DB). Also, the photo-oxidation of hazardous herbicides by strong oxidizing agent hydrogen peroxide in the presence of UV radiations is also investigated. The UV + H 20 2 combination generates hydroxyl radicals having very high oxidation potential which helps in complete mineralization of a herbicide. The photo-oxidation process is found to be strongly pH dependent. The electochemical behaviour of these six herbicides is found to be different which is due to the varying number of chlorine atoms in the aromatic moiety and the different aliphatic side chains. It is observed that UV irradiation increases selectivity as well as sensitivity of the electrochemical reaction. Further, the photo-oxidative degradation by UV + H 20 2 combination is found to cause complete mineralization of herbicide pollutants. The rate of this process is directly proportional to intensity of UV radiations and pH of the medium. Also, a mathematical model on kinetics of degradation of herbicides is developed so as to estimate herbicide residues in soil and vegetation as a function of time for different orders of herbicide decomposition reactions. This may help to understand the fate of environmental pollution caused by herbicide applications.