Phytoextraction of Manganese from Contaminated Carbonate-Rich Soil Amended With Inorganic Amendments
Excessive concentration of manganese (Mn) in contaminated soils poses a serious threat to the environment. Phytoextraction is a biological method for removal of metallic trace elements from contaminated soils. However, dissolution of metal-carbonate minerals and other metal-bearing soil fractions is crucial for a successful phytoremediation. The phytoavailability of Mn in contaminated soils can increase under acidic conditions. The objective of this study was to evaluate the effect of acidification of a metal-polluted soil containing carbonates on the distribution of Mn in four soil fractions as well as on Mn accumulation in biomass of four plant species. Several portions (600 g of soil were treated with 100 ml of H2SO4 solution (0.01N and 0.1N) and 2.95 g of elemental sulfur (S). After harvesting, the Mn in soils was fractionated into "exchangeable", "carbonate" and "oxides" forms. Organically bound Mn was extracted by using pyrophosphate method. The majority of Mn in the soil samples was present in the oxides and residual fractions. The amount of exchangeable Mn was very low (< 0.8 % of total Mn). Exchangeable and carbonate fractions represented less than 3.5% of total Mn. Oxalate-extractable Mn ranged from 26 to 37% and pyrophosphate-extractable Mn ranged from 13 to 23% of total Mn. Tissue Mn concentrations ranged from 75 to 238 mg/kg in shoots, well within the sufficiency range (20-300 mg/kg) for most agricultural crops. Mn uptakes by plants grown in soils treated with S-amendments were higher than those grown on soils without amendments. Application of elemental S resulted in increased uptake of Mn by plant shoots. S-amendments added before planting may accelerate the phytoextraction of Mn from contaminated carbonate-rich soil.
Index Termsó Heavy metal, Phytoremediation, Trace element, Pollution, Decontamination.