Accumulation characteristics of cadmium and its upper critical levels in selected vegetable species

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Abstract
In a greenhouse experiment, five vegetable species belonging to four families, i.e. Chenopodiaceae, Leguminosae, Umbelliferae and Cruciferae were grown on a coarse texture soil amended with different rates of Cd (0 to 100 mg kg‐1 soil). Yields versus Cd addition rate relations exhibited significant yield reductions at addition rates exceeding 10 mg Cd kg‐1 soil in almost all the vegetable crops under study. The Cd content of aerial parts of the plants (tc) was correlated with the DTPA‐extractable soil Cd level (sc) in a double‐logarithmic relationship: log (tc) = α + β log (sc). The regression coefficients α and β were estimated for each species. Based on α values, plant families were divided into three categories: (1) low accumulators, Leguminosae (2) moderate accumulators, Umibelliferae and (3) high accumulators, Chenopodiaceae and Cruciferae. For characterization of Cd accumulation, α values proved more descriptive than the values of β. The threshold levels of Cd toxicity in plant tops of spinach, pea, carrot, radish and turnip were 13, 6, 15, 30 and 70 mg kg‐1 dry matter, respectively. Based on the Ct values, leguminosae proved sensitive and cruciferae tolerant to Cd toxicity.