Pollution, Ecological, and Health Risk Assessments of Heavy Metal Remediated Soils by Compost Fortified with Natural Coagulants

The present study assessed the pollution, ecological, and health risks of heavy metal (HM) remediated soils by compost fortified with the leaves of natural coagulants [Moringa oleifera (Moringa), Azadirachta indica (Neem), and Carica papaya (Pawpaw)]. The polluted soils were treated with the stabilized composts at varying ratios of 1:200, 1:100, 1:66, and 1:50. Castor oil plants were also introduced to compliment the remediation experiment. Heavy metals (Cu, Zn, Ni, Mn, Cd, and Pb) were determined in samples using Atomic Absorption Spectrophotometry. Data collected were analyzed for descriptive and inferential statistics. The HM’s removal efficiency by different compost types in polluted soils was determined. The health risk were also evaluated for hazard quotient (HQ), hazard index, and cancer risk (CR). Manganese (179.6 ± 1.25 mg kg−1 in Neem to 214.7 ± 8.01 mg kg−1 in Pawpaw) was the highest observed HM in composts. The concentrations of HMs (except Zn) determined in composts were generally less than the target values expected in unpolluted soil. Application of the three different compost types to the polluted soils reduced the HMs by 5–37, 17–47, 25–43, 43–57,59–71, and 69–75% for Cd, Cu, Ni, Pb, Mn, and Zn, respectively. Reduction of HMs from the contaminated soils followed the pattern of Zn > Mn > Pb > Cu > Ni > Cd. All the compost types were effective in reducing Mn and Zn from contaminated soils. However, Moringa appeared to indicate the highest removal efficiency followed by Neem and Pawpaw. The HQs of Pb (in the polluted soil exposed to by adults, and the polluted and remediated soils exposed to by children) were > 1.0, indicating an adverse effect. The CRs for Cd, Pb, and Ni in contaminated soil were higher than the permissible limit of 1.0 × 10–4 establishing possible carcinogenic effects.