MICROBIAL AND VERMICOMPOST ASSISTED PHYTOREMEDIATION OF HEAVY METAL CONTAMINATED SOIL IN SHIKIRA, NIGER STATE, NIGERIA

Abstract

In Nigeria and other parts of the world, heavy metal pollution is becoming increasingly common due to anthropogenic activities in agriculture, industries, mining, coal-burning power plants and metallurgical operations. This study was designed to remediate the polluted soils of Madaka District of Shikira Communities comprising Angwan Kawo (AK) and Angwan Magiro (AM) of Rafi Local Government Area, Niger State, Nigeria. Physical & chemical properties of the soil and the vermicompost were assessed using standard methods. Microbial loads of the soil under remediation were monitored from the month of April to October, 2020. Chicken dropping vermicompost (CDV) and goat manure vermicompost (GMV) were produced by standard methods to assist the phytoremediation process together with plant growth promoting bacteria (PGPB, Bacillus safensis). Heavy metals in plants parts were determined using atomic absorption spectrophotometry (AAS). Percentage metal removal was determined using canonical discriminant functions. Soil structural changes, pre and post remediation, were determined through x-ray fluorescence spectroscopy (XRF). Soil remediation was further confirmed by scanning electron microscopy (SEM), which revealed structural and morphological changes of the soil. The soil from the two locations (AK and AM of Madaka district) had significant effect on organic matter OM (p<0.05), total nitrogen TN and Potassium K (at p<0.01), while the two plants significantly affected the pH, organic matter (p<0.05) and total nitrogen (p<0.01). Meanwhile, the time (duration of the experiment) had significant effect on all the parameters at p<0.01 except for exchangeable acidity. Location and plant interactions had significant effect on Mg only (p<0.05); location and time interactions were significant on pH, organic matter and Na contents (p<0.01), also on Ca (p<0.05) while plant and time interactions were only significant on organic matter (p<0.05). The bacterial counts ranged from 0.33±0.6 -11.0± 0.57 (x105 cfu/g) while the fungal counts ranged from 0.00±0.00 - 34.33±26.34 (x102 cfu/g). The bacterial isolates identified in the polluted soil were Bacillus megaterium, Lactobacillus bulgaricus, Lactobacillus acidophilus, Staphylococcus aureus, Bacillus subtilis, Bacillus licheniformis, Pseudomonas aeruginosa and Micrococcus luteus. For AK soil of Melissa officinalis L parts mopped up the heavy metals: Cd, As, Pb on the range: 0.007 - 0.33 mg/kg, 0.09 - 4.39 mg/ kg and 0.07 - 10.35 mg/kg respectively. The concentration of Cd in the residual soil varied from 0.026 to 0.58 mg/kg, As (0.32 - 5.48 mg/kg), Pb (5.88 - 12.37 mg/kg) while in Sida acuta parts Cd, As, Pb varied from 0.002 to 0.43 mg/kg, 0.27 - 3.79 mg/ kg and 1.68 - 10.7 mg/kg respectively. The concentration of Cd in the residual soil varied from 0.023 to 0.24 mg/kg, As (0.07 - 5.34 mg/kg) and Pb (6.74 - 11.8 mg/kg) after remediation of AK soil. Angwan Magiro (AM) had the two plants mopping up heavy metals at different rates. The concentrations of Cd, As, Pb in M. officinalis L parts varied from 0.03 to 0.41 mg/kg, 0.65 - 4.65 mg/ kg and 1.93 - 11.49 mg/kg respectively. The concentration of Cd in the residual soil varied from 0.016 to 0.29 mg/kg, As (1.03 - 10.39 mg/kg) and Pb (7.83 - 20.24 mg/kg) while in S. acuta parts Cd, As, Pb varied from 0.06 to 0.66 mg/kg, 0.68 - 4.64 mg/ kg and 1.53 - 11.53 mg/kg respectively after seven time. The concentration of Cd in the residual soil varied from 0.016 to 0.34 mg/kg, As (4.43 - 9.36 mg/kg) and Pb (10.63 - 25.92 mg/kg). Melissa offinalis L and Sida acuta were found most suitable for phytoextraction of sites contaminated with Cd, As and Pb because both plants had their bioconcentration factor (BCF), translocation factor (TF) and biological accumulation coefficient (BAC) to be ˃1. The two plants also served as phytostabilizers because they had BCF ˃1 and TF ˂1. However, the two plants had no characteristics of hyperaccumulator, judging from the fact that both had enrichment factor (EF) ˃ 1 and none of the plant species was found to have accumulated the heavy metals higher than 1000 mg/kg. The results demonstrated the elongation and disappearance of peaks in the polluted and the remediated soils, suggesting that remediation had taken place and the soil had been restored by the process. Melissa offinalis L and Sida acuta when assisted with CDV, GMV and PGPB proved highly effective in remediating the heavy metal polluted soil.