Soil adsorption study of Dimethoate to evaluate its leaching potential by spectrophotometry

With a view to study the leaching potential and consequently surface and ground water contamination, the adsorption of dimethoate on five soils of different characteristics has been carried out by using a batch equilibrium technique. A spectrophotometric methodology based on the reaction of thioglycolic acid, formed from microwave assisted alkaline hydrolysis of dimethoate, with carbon disulfide and nickel(II) acetate to form methyl isobutyl ketone extractable yellow colored nickel(II)-thioxanthate complex showing λmax at 378 nm has been developed for the purpose. The molar absorptivity (ε) and Sandell’s sensitivity were found to be 1.2×10 3 L/mol cm and 0.19 μg/cm 2 respectively. The leaching potential has been evaluated by Groundwater Ubiquity Score (GUS) and the values obtained in the range 1.85-2.45 classify dimethoate as a transition pesticide and thereby it poses a potential risk to the aquatic environment.