Mobility of203Hg-Labelled Mercuric Chloride in Soil Columns

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Abstract
The mobility of 203Hg-labeled mercuric chloride in soil columns of the Dar es Salaam (Entisol) and Arusha (Inceptisol) soils from Tanzania was investigated by external scanning measurements as well as by activity measurements in column segments. Leaching rate was 0.44 cm/h both with single and sequential leaching with water and salt solutions. There was limited mobility, 2 and 4 cm in soil columns of Arusha and Dar es Salaam soils, respectively, when leached with water or diluate solution of CaCl2 (0.01 M). Sequential leaching with 0.5 M CaCl2 and 0.1 M EDTA resulted in detectable Hg mobility to a depth of 8 cm in both soils. The 203Hg activity profiles by external scanning correlated very well with the contents of Hg in the column segments, determined after sequential leaching. The correlation coefficients were 0.709* and 0.826* for Arusha and Dar es Salaam soils, respectively. External scanning measurements reflected satisfactorily the Hg status inside the soil columns, and thus offers the possibility of in situ monitoring. The limited mobility suggests that ground water pollution by mercury under normal conditons of leaching is unlikely.

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