Effect of biochar amendment on the bioavailability of lead (Pb) in contaminated soils of Kabwe, Zambia.

Biochar is an organic residue combusted under low oxygen conditions, resulting in a porous, low-density carbon-rich material. Biochar has the potential to reduce pollutant mobility when used as an organic soil amendment. Until recently, Biochars’ potential has not been extensively evaluated for this purpose. To that purpose, a greenhouse experiment was conducted to assess the effect biochar derived from maize corncobs on bioaccumulation of Lead (Pb) in Chinese cabbage (Brassica pekinensis) and Tithonia (Tithonia diversifolia). The soil biochar mixture was made on biochar/soil weight basis at the rate equivalent to 0 (control), 2, 4 and 8 % biochar of the soil weight which was seven (8) kg. The plants were grown in pots at the above mentioned four application rates and these application rates were replicated four times. The study results showed that there were no significant differences (p > 0.05) in the available Pb in the 0, 1 and 8% treatments for the Tithonia and Chinese Cabbage Pb contaminated soils. When the various plant parts were analyzed for Pb uptake across all treatments, only Tithonia at the application rate 8% had recorded a significant reduction (p<0.05) and a decreased uptake of 23.8% when compared to the control. Additionally, biomass yield comparison across all treatments showed that biochar application rate of at 8% significantly (p<0.05) increased yield at the rate of 20.3%. The results indicated that Pb could not be significantly (p<0.05) leached out of the soil profile. Thereby, implying that biochar application decreased the bioavailable Pb as well as its mobility at a higher application rate of 8%. Thus, this study provides results that show that biochar has the potential to reduce available Pb in contaminated soils.