ASSESSMENT OF HEAVY METALS CONTAMINATION OF THE SOIL IN OKITIPUPA MARKET AREA OPEN-AIR DUMP SITE

This study assessed the contamination of soils by heavy metals at Okitipupa market area dumpsite in Okitipupa Local government Ondo State, Nigeria. Soil samples were collected from five designated points within the dumpsite (North, South, East, West, and Centre) as well as control site which is at a distance outside the dumpsite. At each point, samples were taken at three depths (0–10 cm, 10–20 cm, and 20–30 cm). The collected samples were air-dried, sieved, and analysis of the physicochemical properties and heavy metals was made possible using Atomic Absorption Spectrophotometry (AAS), Atomic Fluorescence Spectroscopy (AFS) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). The results revealed that Okitipupa market area dumpsite soils were generally acidic (pH 5.6–7.8), with higher electrical conductivity (up to 1760 µS/cm) and organic matter (up to 3.47%) concentrated in the topsoil. Among the heavy metals, iron (Fe) and zinc (Zn) were the most dominant, reaching concentrations of 26.1 mg/kg and 11.0 mg/kg respectively, while copper (Cu) was found in smaller amounts (0.055–0.312 mg/kg). Toxic heavy metals such as lead (Pb), cadmium (Cd), chromium (Cr), and nickel (Ni) were either absent or detected only in very small traces, with lead peaking at 3.25 mg/kg. Contamination index values for all metals were noticed below 1, indicating that the soils are not yet heavily polluted. However, ecological risk assessment showed that cadmium and lead, despite their low concentrations, posed higher potential risks due to their toxicity and ability to bioaccumulate. The study concludes that, Okitipupa market area dumpsite soils are moderately impacted by waste disposal, with contamination largely restricted to the top and mid-soil layers. Although current levels of pollution remain within permissible limits, the presence of cadmium and lead signals a need for regular monitoring and improved waste management practices to prevent future environmental and health hazards.