Analysis of Soil Quality Status and Accumulation of Potentially Toxic Element in Food Crops Growing at Fecal Sludge Dumpsite in Ubakala, Nigeria

Abstract

This study investigated the magnitude of potentially toxic element (PTE) in fecal sludge and the level of contamination of soil and food crops at Ubakala, Abia State, Nigeria. Soil samples were collected in four cardinal points at north (N), south (S), east (E) and west (W) of 1 m, 5 m, 15 m and 30 m from the edge of the fecal sludge dumpsite and standards (2 ppm, 4 ppm and 6 ppm) were prepared from 1000 ppm stock solution of the metals and used to plot the calibration curve with Atomic Absorption Spectrometer. Commonly consumed Carica papaya, Telfairia occidentalis and Manihot esculenta leaf samples were collected and analyzed to measure the concentrations of PTEs such as Cd, Zn Cr, Mn, Pb and Cu. The concentrations of Zn (12.41±0.30 mg/kg), Cd (0.07±0.00 mg/kg), Cr (4.47±0.34 mg/kg), Cu (2.12±0.03 mg/kg), Mn (8.13±0.03 mg/kg) and Pb (0.01±0.00 mg/kg) in dried fecal sludge are below the permitted limits of European Union. Concentrations of PTEs in soil and plants were Zn (13.40±1.20 to 100.80±1.40 and 1.24±0.06 to 56.02±5.02 mg/kg), Cd (0.07±0.01 to 0.92±0.02 and 0.0000±0.000 to 0.085±0.01 mg/kg), Cu (6.27±0.31 to 31.39±1.04 and 0.002±0.001 to 10.80±2.01 mg/kg), Mn (36.00±1.56 to 188.57±2.25 and 0.11±0.00 to 17.21±2.01 mg/kg), Cr (2.40±0.40 to 21.03±1.43 and 0.000±0.00 to 9.60±1.13 mg/kg) and Pb (0.09±0.02 to 0.35±0.03 and <0.00001±0.00 to 0.008±0.00 mg/kg), respectively. Zinc in soil is higher than FAO/WHO permissible limit while Cd in soil is higher than FAO/WHO limit and Dutch criteria for soil. Zinc and Cr in food crops are higher than FAO/WHO permissible limit. Strong positive relationship exist between Zn in soil and food crops (r = 0.616, p<0.05). Based on the findings, it is recommended that the fecal sludge should be treated with lime to precipitate PTE content of sludge and lowering the corresponding environmental risks.