Accumulation of metals in vegetation from an alkaline artificial soil

This research was conducted to determine whether elevated concentrations of metals in biosolids would result in increased accumulation of these metals in plants growing on an alkaline, artificial soil created by addition of municipal sewage biosolids to inorganic waste materials during reclamation of a filled lime settling basin. Accumulation of metals in vegetation growing on this alkaline, artificial soil was compared with accumulation in vegetation growing on a natural, reference soil that had not been amended by biosolids. Although the concentrations of Cd, Cr, Hg, Ni, Ag, and Zn were greater in the artificial soil than in the reference soil, only Cd was found at greater concentrations in vegetation growing on the artificial soil. These greater concentrations were only observed in wheat grass (Agropyron sp.), and not in orchard grass (Dactylis glomerata L.). Also, the accumulation ratio, which is the ratio of the metal concentration in plant tissue to that in the soil, for wheat grass was much lower than other published values. There were no differences in the concentrations of Ba and Pb in the two soils, but the concentrations of these two metals in orchard grass growing on the reference soil were greater than that in either grass on the artificial soil. The differences in plant uptake of metals appear to result from differences in soil pH between the artificial and reference soils. Many metals are generally more soluble and bioavailable at the lower pH of the reference soil (pH = 5.4-6.6) than at the higher pH of the artificial soil (pH = 7.8-8.2). As a result, transfer of metals to vegetation growing on the alkaline, artificial soil is less than that in vegetation growing on the reference soil despite the greater concentrations of metals in the artificial soil.