Immobilization of lead by a vermicompost and its effect on white bean ( Vigna Sinenis var. Apure  ) uptake

Lead is one of the most dangerous contaminants which has been released to the environment during many years by anthropogenic activities. Adsorption of Pb²⁺ on vermicompost was studied at 11°C, 30 °C and 50 °C by using Langmuir and Freundlich models, that adequately described the adsorption process, with maximum adsorption capacities were 116.3; 113.6 and 123.5 μg/g for each temperature. The differences in FTIR (Fourier Transform Infrared Spectrometer) spectra of vermicompost at pH 3,8 and pH 7.0 in the region from 1800 to 1300 cm^-1 were interpreted on the basis of carboxyl acid ionization that reduce band intensity around 1725 cm^-1 producing signals at 1550 cm^-1 (υ_a) and 1390 cm^-1 (υ_a) of carboxylate groups. Similar changes were detected at pH 3.8 when ionic lead was present suggesting that heavy metal complexation occurs throughout a cationic exchange reaction. Vermicompost was applied to a soil where white bean plants were planted. After irrigation with lead nitrate solutions the uptake of lead was reduced to 81 % in leaves and stem, while the reduction in the roots was around 50 %. The highest accumulation of lead was found in the roots and the translocations seems to be limited by the presence off vermicompost in the soil.