HEAVY METALS

This study was carried out to determine the concentrations of some heavy metals, such as nickel, cadmium, mercury, and oxidative stress status of tomatoes sold in local markets in Benin City, Edo State, Nigeria. Fresh tomato samples were brought from Uselu and Ikpoba Hill market in Benin City. The samples were oven-dried at 105°C for 24 hours and grinded to powder. The powdered samples were dissolved in deionized water, filtered through Whatman filter paper, and the volume was made up to 25 ml using 10 ml of 98% nitric acid. The resulting solution was analysed for the presence of heavy metals using an Atomic Absorption Spectrophotometer
(AAS, Perkin Elmer model 2130). The results showed that the nickel concentration present fresh tomato samples obtained from the two markets ranged from 0.13 mg/kg to 0.16 mg/kg, while
the cadmium concentration ranged from 0.11 mg/kg to 0.13 mg/kg. However, when compared to
W.H.O standard, the heavy metal concentration was slightly above the recommended value of
0.10 mg/kg. Also, oxidative stress analysis showed that the superoxide dismutase (SOD) value
ranged from 3.02 U/g to 3.48 U/g, Catalase (CAT) value ranged from 0.08 U/g to 0.10 U/g, the glutathione peroxidase (GPx) value ranged from 4.96 U/g to 5.73 U/g, while the malondialdehyde (MDA) value ranged from 0.50 U/g to 0.64 U/g respectively. These findings were indicative of environmental pollution due to industrial and vehicular emissions and also the mode of handing and processing of the samples. Although the heavy metals detected in this study are not beneficial to man and plant, low concentration can prove detrimental to health.

With Nigeria generating over 42 million tonnes of waste annually, improper disposal poses significant risks to soil health, groundwater, and public health. This study examines the contamination levels of heavy metals and the physicochemical properties of soil at a solid waste disposal site in Ovia Northeast, Edo State, Nigeria. Soil samples were collected at varying depths (10, 20, 30, and 40 cm) from a dumpsite and a control site, focusing on lead (Pb), iron (Fe), copper (Cu), and manganese (Mn), alongside properties such as pH, bulk density, porosity, organic matter, and electrical conductivity (EC). Results revealed elevated levels of heavy metals at the dumpsite compared to the control site, particularly in the top 10 cm of soil. For example, Pb concentrations reached 12.31 mg/kg at the dumpsite, nearly three times higher than the 4.24 mg/kg observed at the control. Similarly, copper (Cu) levels at the dumpsite peaked at 74.22 mg/kg, significantly higher than the control site’s 57.47 mg/kg. Physicochemical properties demonstrated a strong influence on metal mobility: soil pH at the dumpsite ranged from 7.12 to 7.62, slightly higher than the control’s 6.86 to 6.12. Organic matter content decreased with depth, from 8.74% at the surface to 3.15% at 40 cm in the dumpsite, compared to 9.07% to 2.54% in the control. EC values were markedly higher
at the dumpsite (252–290 µS/cm) compared to the control (144–168 µS/cm), reflecting leachate infiltration and ion enrichment. The findings underscore the environmental risks posed by heavy metal contamination, including soil degradation, reduced fertility, and potential bioaccumulation in the food chain. Elevated
metal concentrations exceeded WHO permissible limits, necessitating immediate remediation actions. Recommendations include the implementation of sustainable waste management
practices, soil remediation techniques such as phytoremediation, and ongoing monitoring to mitigate long-term environmental impacts.