Effect of Ethylenediaminetetraacetic Acid and Ammonium Oxalate on the Prevalence of Microorganisms and Removal of Aluminum in Soil by Bitter Leaf Plant (Vernonia amygdalina Delile)

Abstract

This research was carried out to investigate effect of ethylenediaminetetraacetic acid and ammonium oxalate on the prevalence of microorganisms and removal of aluminum in soil by bitter leaf plant (Vernonia amygdalina). The test plant was sown in aluminium-polluted soil (conc. = 150mg Al kg^-1 soil). One gram of each chelating agent was dissolved in 1.5 litres of water and applied at different time intervals; application on a day prior to sowing of test plant in metal-polluted soil, application on the day of planting, application at one week after planting; at one month after planting. For the control soils, chelating agent were not added, although aluminium-contaminated. In the control, aluminium concentrations in leaf tissues were 16.20mg/kg compared to a staggering 9.20mg/kg in EW1 and 5.24mg/kg in OD1. However, heavy metal concentration of the leaves of Vernonia amygdalina in the control, EW1, EM1, OD-1 and OW1 were significantly similar (P>0.05). Concentration of aluminium in the stem tissues were also similar in ED1, EM1, OD-1, OD1 and OW1 (P>0.05) were concentration ranged from 5.42mg/kg to 7.98mg/kg. Compared to the control, aluminium concentration in stem tissues was 4.95mg/kg comparable with 3.42mg/kg in OM1. In the plant root, OD1 had the highest accumulation of aluminium in the root (16.92mg/kg); however concentrations of aluminium in the roots were also statically similar in OW1 (15.08mg/kg), OM1 (13.84mg/kg), OD-1 (14.72mg/kg), EM1 (15.12mg/kg) and in the control (13.52mg/kg). Results of the following also showed concentrations of residual aluminium in the soil ranging from 68.25mg/kg in the control to 109.85mg/kg in ED1 soil. After three months of planting, results show that the total bacteria count for ED1 (5.3 × 10⁴ cfu/g) had the highest while OM1 (3.9 × 10³ cfu/g) had the lowest. For fungi isolates, the highest was control (8.2 × 10³ cfu/g) whereas the lowest were OD–1 (6.8 × 10² cfu/g). The most prevalent microorganisms in the spiked soil with heavy metal are Bacillus subtilis represented in all the samples for bacteria while Aspergillus niger representing fungi. The perseverance of the test plant in the aluminium spiked soil is an indication of adaptation to the stress imposed by the concentration of aluminium in soil. In spite of the metal composition within the soil, it was observed that a number of microorganisms existed. This may therefore suggest a favourable environment for the microorganisms within the soil rhizospheric region of Vernonia amygdalina.

Keywords: EDTA, oxalate, aluminium, pollution, remediation, Vernonia amygdalina