ESTIMATION OF MAXIMUM PERMISSIBLE LEVELS OF CADMIUM IN A LIGHT SOIL BY USING CEREAL PLANTS

A pot experiment was conducted in a greenhouse to establish the thresh old level of Cd in a light soil planted with cereals. During three con secutive years barley, wheat, rye, and com were grown in the soil trea ted with 2.5; 5; 25 mug g-1 of Cd applied in sulphate form. The Cd con centration of 5 mug g-1 (plus native Cd content of the soil) was consi dered as the maximum permissible Cd level in a soil for the soil-plant systems studied. Besides the estimation of total Cd concentrations, s everal forms of Cd in soils (exchangeable, carbonate, Fe-Mn oxides, or ganic, and residual) were determined by mean of sequential extraction to define the phytoavailable form of Cd in the soil. The Cd concentrat ion in studied plants increased with the doses of this metal in soil b ut to different extents for various plant species and various plant pa rts. The highest Cd enrichment ratios (ER) were found for wheat and co rn leaves (2 to 3), whereas, the lowest ERs were detected for com and rye grains (0.05 to 0.2) grown at the treated soils. All samples of th e control plants had ER below 1. A close relationship was found betwee n Cd content of plants and the exchangeable form of Cd in soil, which indicates that this form of the element is readily available for plant s. The proposed maximum permissible level of Cd (5 mug g-1 of added me tal plus native Cd content of soils) in light soils proved to be too h igh for cereal plants. The threshold concentration for light soil shou ld not exceed 3 mug g-1.