Abstract:
ABSTRACT
The presence of toxic heavy metals such as Cr, Pb, Ni, As and Hg in foods constitute serious
threat to the health of consumers, particularly humans. Continual consumption of foods with
high level of toxic metals can lead to bioconcentration and bioaccumulation with long-term
health implications. This study was carried out in Tsumeb, Grootfontein and Otavi local
municipal areas in the Oshikoto region of Namibia. The focus was to assess the level,
distribution and chemical mobility of selected toxic heavy metals in soil and farm produce
from agricultural farmlands from these local municipalities. An experimental research design
was used in the process of data collection. Soil and food samples from farms were collected
over a period of two years. Samples were pre-treated and heavy metals content extracted
using mineral acid microwave assisted digestion protocol. Qualitative and quantitative
analysis of the metals was by the Inductively Coupled Plasma-Optical Emission Spectroscopy
(ICP-OES).
The mean concentration of heavy metals in soil samples across the period ranged from 0.8
mg/kg; 1513.72 mg/kg; 7.97 mg/kg; 1.21 mg/kg; 2.03 mg/kg 13.18 mg/kg and 9.36 mg/kg
from Tsumeb. The level in Grootfontein varied from 0.12 mg/kg; 1317.07 mg/kg; 7.97 mg/kg;
0.08 mg/kg; 1.61 mg/kg and 1.35 mg/kg and 8.18 mg/kg, while the concentration from Otavi
ranged from 0.41 mg/kg; 1082.9 mg/kg; 7.96 mg/kg; 0.53 mg/kg; 1.75 mg/kg 7.82mg/kg and
8.49 mg/kg for Cr, Mn, Hg, Ni, Cu, Zn and Pb respectively. The mean concentration of these
toxic metals in food samples across the period also ranged from 5.8 mg/kg; 12.49 mg/kg; 0.68
mg/kg; 1.27 mg/kg; ND and ND from Tsumeb. The level in Grootfontein varied from 1.7
mg/kg; 153.5 mg/kg; 0.41 mg/kg; 1.42 mg/kg; 5.13 mg/kg and 13.22 mg/kg 2.06 mg/kg, while
the concentration from Otavi ranged from 0.64 mg/kg; mg/kg; 62.3 mg/kg; 0.65 mg/kg; 0.61
mg/kg and 7.33 mg/kg 13.87 mg/kg 4.38 mg/kg for Cr, Mn, Hg, Ni, Cu, Zn and Pb respectively.
Analyzed metals were widely distributed in both soil and food samples. Metallic accumulation
factor (AF) of > 1 was obtained in Manganese, Copper, Nickel and Zinc food samples which
revealed chemical mobility of metals from labile metals fractions obtained in soil samples.
The mean concentrations of 77.7mg/kg, 60.0 mg/kg, 17.8 mg/kg and 50.4 mg/kg for
Manganese, Copper, Nickel and Zinc respectively obtained in food samples were found to be
higher than permissible levels in foods.
