Abstract

In this paper we evaluated the effects of various amendments, notably zeolite, red mud (a by-product of aluminium manufacturing) and lime on decreasing the bioavailability and phytotoxicity of Pb, Cd and Zn present in a contaminated acidic soil (pH = 4.2). Pisum sativum and Triticum vulgare were grown in a glasshouse experiment on untreated-polluted (control) and amended soils and their yield and metal uptake determined. The influence of plants on the total concentration and mobility of Pb, Cd, and Zn, and on several soil microbiological and biochemical parameters was also evaluated and compared to unplanted (control and amended) soils on which we have previously reported.
All the amendments enhanced plant yields significantly. Red mud and lime decreased Zn, Pb and Cd availability to plants, whilst zeolite was efficient only at blocking Pb. Red mud in particular decreased heavy metal uptake of pea and wheat by 60–34% (Pb), 79–80% (Cd), and 93–64% (Zn) respectively when compared to the control plants.
After plant growth, Cd and Zn solubility in the amended soils was significantly higher than in respective unplanted soils. Likewise, the number of fast-growing heterotrophic bacteria and fungi was higher after pea and wheat compared to bare soil, and this was irrespective of the treatment applied. These data together with Biolog-derived parameters (AWCD and richness) and enzyme activities (dehydrogenase, urease and β-glucosidase) also suggested that pea rhizodeposits, in the different soils, were either more abundant or more readily-available to soil bacterial communities compared to wheat rhizodeposits.

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