Validation of a Spectrofluorimetric Method for the Determination of Thiram and Thiophanate Methyl Fungicides in Environmental Samples

The intensive use of thiram and thiophanate methyl fungicides in agriculture leaves residues on crops and contaminates groundwater and surface water bodies through leaching. For the purpose of monitoring pollution arising from their presence, a spectrofluorimetric method has been validated for screening these fungicides in environmental samples viz. water, soil and foodstuffs. The measurement of fluorescence intensity of cerium(III) species at 365 nm resulting from ceric ammonium nitrate oxidation of dimethyl dithiocarbamate and o-phenylene bis-thiourea (products of the reaction of thiram and thiophanate methyl, respectively, with potassium tert.-butoxide) formed the basis of the method. As little as 0.18 and 0.22 μg ml-1 of thiram and thiophanate methyl can be determined. A simple and rapid solidphase extraction and purification procedure, prior to the spectrofluorimetric determination, show high recoveries of these fungicides from spiked water and grain samples in the range 86.0-98.0% and 88.5-97.5% with a maximum RSD of 2.60% indicating a good accuracy and precision of the method. The risk of water bodies’ contamination by the two, groundwater ubiquity score (GUS), has also been evaluated using adsorption study on four soils; the values in the range -0.48 to 0.98 classify them as non-leacher fungicides.