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The ability of hydrous oxides of iron (Fe) and manganese (Mn) in municipal biosolids to adsorb metals in the biosolid and in amended soils, and limit the phytoavailability of many trace elements has been documented. We conducted an experiment to test whether deliberate addition of Fe or Mn to sludge compost would reduce the potential for cadmium (Cd) uptake by lettuce (Lactuca sativa L.) from soils that had been amended with high Cd sewage sludge in the 1970s. Results from this study may be applicable to remediation of contaminated soils, as well as to preparation of designer biosolids, which lower metal phytoavailability and bioavailability. Soils were obtained from fields that received high Cd sludge (",1000 mg Cd kg-' and 1000 mg zinc (Zn) kg-', dry wt); the Cd was discharged by a user of Cd pigments. In field trials with 2% limestone addition to a depth of 30 cm, lettuce and spinach (Spinacia oleracea L.) contained >50 mg Cd kt', dry wt. In addition to Fe and Mn addition to increase metal adsorption, Zn addition was included in the study because our research has demonstrated that added Zn inhibits Cd uptake and translocation by plants. The treatments included factorial additions of Fe, Mn, and Zn to the compost; 10% compost by dry weight was added to the test soil; 2% reagent

Wheat grown on cadmium (Cd)-uncontaminated soils can still potentially translocate unacceptable levels of Cd to grain. The effect of zinc (Zn) and Cd levels on Cd uptake and translocation in ''Grandin'' hard red spring wheat (HRS-wheat) (Triticum aestivum L.) was investigated using a double chelator-buffered nutrient solution [EGTA used to buffer Cd, Zn, copper (Cu), manganese (Mn), and nickel (Ni); and Ferrozine (FZ) used to buffer Fe 2þ ]. In the Zn level series of treatments, Cd 2þ activity was held constant at 10 À10.7 M, and the Zn 2þ activity was varied from 10 À7.6 to 10 À5.2 M. As Zn 2þ activity increased, the translocation of Cd to the shoots decreased. The shoot : root Cd concentration ratio decreased from 0.20 to 0.03 as pZn 2þ went from 7.6 to 5.2, indicating that adequate to high levels of Zn are effective in reducing Cd translocation to the shoots of ''Grandin'' HRS-wheat. In the Cd series, the Zn activity was at 10 À6.6 M, while Cd activity was increased from 10 À10.7 to 10 À9.2 M. High levels of Cd did not significantly affect the uptake and translocation of Zn in the roots and shoots. While at pCd 2þ of 9.2, the root and shoot Cd concentrations significantly increased, there was not a significant increase in the shoot : root Cd ratio. This would indicate that even at high Cd 2þ activities, Zn is effective in regulating Cd uptake and translocation in ''Grandin'' HRS-wheat.

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