Bioavailability and contamination levels of Zn, Pb, and Cd in sandy-loam soils, Botswana

摘要

Poultry litter and its biochar has been used recently as alternative effective soil organic amendments due to their significant effect of improving soil properties. However, detailed information on this organic amendment's contribution to the bioavailability of heavy metals in the soil is still lacking. Hence, this study was designed to evaluate the effects of incorporated poultry litter and its biochar on bioavailable Zn, Pb, and Cd concentrations in the soil using various assessment contamination methods. The soil samples treated with poultry litter and its biochar at different application rates of 0, 15, 30, 60, 120 g/kg were collected from a greenhouse pot experiment. The study results indicate a decreasing order in concentrations as follows; Zn (2.04 mg/kg) Pb (0.22 mg/kg) Cd (0.02 mg/kg). Geoaccumulation Index (I-geo) for Zn was moderate (0 I-geo 1) to heavy contamination (I-geo = 1.00), while Pb I-geo values were within the moderate contamination (0 I-geo 1) in all treated soils. Furthermore, Zn and Pb yielded contamination factor (CF) values within the ranges of low contamination (CF 1) to moderate contamination (1 CF 3), nonetheless Zn exhibited the highest CF compared to Pb and Cd. Higher values of Pollution Load Index (PLI 1) were observed, indicating the pollution level. Those PLI values point out the need to evaluate bioavailable heavy metals levels rather than total metal concentration for risk assessment of soil contamination by organic amendments.