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Research was undertaken to develop practicable laboratory methods for assessing the solubility and plant-availability of potentially hazardous trace metals accumulating in arid-zone soils receiving sewage effluents or sludges. Sequential extraction of field soil samples with potassium nitrate, water, sodium hydroxide, sodium EDTA, and nitric acid was shown to provide reliable estimates of trace metal solubility and uptake (leaf concentration by barley, irrespective of soil texture, rate of sludge application, or time during a three-year study period. The total concentrations of the trace metals Ni, Cu, Zn, Cd, and Pb accumulated in two sludge-amended field soils during the project period were comparable with the amounts of these metals sorbed by untreated soils at soil solution concentrations below 100 parts per billion. At these low metal concentrations, the sorption isotherms often exhibited a sigmoid shape that precludes interpretation of terms of conventional distribution function techniques. Organic forms of the trace metals, particularly copper, were found to increase in importance with the sludge application rate. These organic-metal compounds could be characterized conveniently by electron spin resonance spectrometry.


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