HEAVY METALS

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.

The study assessed the levels of heavy metals in soils near sand mining sites in Iyuku, Auchi, Edo State, Nigeria and evaluated associated non-carcinogenic health risks through incidental ingestion. Soil samples were collected from ten locations, air-dried, sieved and analyzed for Fe, Zn, Cu, Pb, Cd, Mn, Ni, Cr and Co using atomic absorption spectrophotometry after aqua regia digestion. Mean concentrations were highest for Fe (56.24 mg/kg), followed by Zn (27.15 mg/kg) and Cu (18.76 mg/kg), with Cd and Co at trace levels (0.45 mg/kg and 0.32 mg/kg, respectively). All values fell below World Health Organization (WHO, 2011) and United State Environmental Protection Agency (USEPA, 1992) soil quality guidelines, indicating limited contamination. Chronic daily intake (CDI) via ingestion was calculated for children and adults, revealing higher exposure in children due to behavioural factors. Hazard quotients (HQ) for individual metals and the hazard index (HI) for combined exposure were all below 1, suggesting negligible non-carcinogenic risks. However, elevated Fe and Zn near active pits highlight the need for ongoing monitoring. The findings underscore the importance of regulatory measures to prevent future escalation of risks in similar mining communities, emphasizing sustainable practices to protect vulnerable groups.

This experiment was conducted in the green house of the Department of Soil Science and Land Management, Faculty of Agriculture, University of Benin, Benin City. The aim of the study was to ascertain the heavy metal (Pb, Cd, Cr and As) contents of Amaranthus cruentus raised on soils from dumpsites from different land uses in the University of Benin. The experiment was laid outin a Completely Randomized Design (CRD) with three replicates. Six different dumpsites were carefully selected in the Ugbowo campus of the University of Benin, three from learning centers and the other three from residential areas (students hostel). Soils collected from the dumpsites were filled into buckets and Amaranthus seeds were planted in them, and harvested at maturity. Soil and plant samples were taken to the laboratory to determine the physicochemical characteristics and heavy metal content present. Data obtained were subjected to Analysis of
Variance (ANOVA) while LSD was used to separate means at 5% level of probability. Results obtained shows that soils from the dumpsites belong to the textural class: sand. Their pH was
moderately acidic and their TOC contents were 19.60 and 21.50 g/kg in the Learning center and Residential area respectively. The heavy metal studied were present in both soils, and there was no significant difference between the heavy metal content across the two dumpsites. The peak lead (Pb) content (1.30 mg/kg) was obtained in the learning center while the peak Cd, Cr, and As contents (0.037 mg/kg, 0.040 mg/kg and 0.040 mg/kg respectively) were recorded in the residential area.