Determination of Methylisothiocyanate in its Commercial Formulation and Different Soils by a Simple Spectrophotometric Method

Methylisothiocyanate is used as soil fumigant for nematodes, fungi etc. It is volatile, contaminate the nontarget areas by diffusion and its exposure can cause various adverse effects to other organisms including human beings. In the present work a simple spectrophotometric method for the determination of methylisothiocyanate in soil is described. It is treated in acetonitrile medium with an excess of n-butylamine to convert it into a substituted thiourea and the surplus amine can be smoothly quantitatively transformed into bright yellow copper(I) n-butyldithiocarbamate through reaction with carbon disulphide and copper(I) perchlorate. The yellow colour formed is stable for at least 120 min and is measured at 360nm. The adsorption isotherms have been evaluated by Freundlich’s adsorption equation and have been found to be S-type. Various adsorption parameters such as (Kd), (Koc), (ΔGo) and (GUS) have also been calculated. The very low values of Koc suggest that methylisothiocyanate is very weekly adsorbed and is highly mobile in soil. The leaching potential of methylisothiocyanate has been evaluated in terms of ground water ubiquity score (GUS) and has been found in the range 1.84-2.02, classifying it as a transient pesticide.