Winter wheat ( Triticum spp. var. Anza) and soils were sampled at the third and the fourth year following the termination of sludge applications to a cropland site to examine the effect of deposited Cd and Zn on crop yield and metal concentrations in plants and the soil. Higher yields of wheat grain, due apparently to the residual N, P, micronutrients, and organic matter from the sludge treatment, were obtained from the sludge‐treated soils than from the controls. Although the treated soils received substantial quantities of Cu, Ni, and Pb, elevated plant‐tissue concentrations of these elements were not found in the wheat grain and straw. The plants, however, extracted greater amounts of Cd and Zn from the sludged than from non‐sludged fields. The metal contents of sludge‐affected wheat straw (0.07–0.16 µ g/g Cd; 19–26 µ g/g Zn) and grain (0.04–0.09 µ g/g Cd; 22–45 µ g/g Zn) were within the range typical for wheat grown on uncontaminated soils. Four years after the termination of sludge disposal, the heavy metals accumulated almost entirely in the 0‐ to 15‐cm soil layer where sludges were incorporated. The elevation of Cd and Zn did not result in any detectable increase in the concentration of water‐extractable Cd and Zn in the sludge treated soils. Attempts to recover heavy metals in the soil failed to account completely for all of the added metals. An average of 67% of the added metals was recovered from the surface 30 cm of the soil profile.
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Chang et al. (1982) studied this question.