Determination of Mobile Thallium in Soil by Flow Injection Differential Pulse Anodic Stripping Voltammetry

A procedure for the determination of mobile thallium in soil has been developed. Free thallium(I) was extracted with deionized water, while the sorbed and exchangeable metal was extracted with 1 M ammonium nitrate. Thallium in extracts was determined by differential‐pulse anodic stripping voltammetry in a flow‐injection system with medium circulation. 0.05 M EDTA was the base electrolyte. The procedure was applied for the determination of mobile thallium in a sample of ground from a waste dump which was a potential source of thallium pollution. The total concentration of thallium in the sample was 17.9 μg g−1. 3.97±0.25% of total thallium was found to be water soluble and 12.4±1.1% was sorbed and exchangeable. An attempt to determine the thallium bound to the carbonate fraction failed because of the high accumulation of interfering lead in this fraction. A single extraction cycle recommended by the literature was not sufficient to extract the whole thallium content of the fraction. Minor rivers of the area of the waste dump have a thallium concentration higher by two orders of magnitude than in reference rivers.