Evaluation of Ecological and Health Risks of Heavy Metals in Selected Hand-Dug Wells around Ido-Osun Landfill Site in Osogbo, Osun State, Nigeria.

Abstract

Background: Groundwater is a vital source of drinking water, especially in developing regions. However, its quality is increasingly compromised by contamination from nearby landfill sites. Objective: This study assessed the physicochemical characteristics and heavy metal concentrations in groundwater around the Ido-Osun landfill, located in Osogbo Local Government Area, Osun State, Nigeria. Methodology: Groundwater samples were collected and analysed using standard procedures. Physicochemical parameters were measured, and heavy metals were quantified using Atomic Absorption Spectrophotometry after acid digestion. Results were compared against World Health Organization (WHO) and Nigerian Standards for Drinking Water Quality (NSDWQ) guidelines. The Water Quality Index (WQI) was computed to provide an integrated assessment of water safety. Results: While most physicochemical parameters fell within acceptable limits, elevated levels of total dissolved solids (TDS: 429.8 mg/L) and nitrate (NO₃⁻: 37.46 mg/L) were recorded in some samples. Heavy metal analysis revealed concerning concentrations of lead (Pb: 0.03 mg/L), chromium (Cr: 0.24 mg/L), and copper (Cu: 0.16 mg/L). The calculated WQI was 358.84, placing the groundwater in the "extremely poor" category. This classification indicates that the water is unfit for drinking without significant treatment, posing immediate health risks. The WQI integrates various water quality parameters into a single value, and such a high score signals serious contamination affecting the overall usability of the water source. The health risk assessment further revealed a high non-carcinogenic hazard index (HI: 29.88), driven mainly by lead exposure (HQ: 29.25), far surpassing the safety threshold of 1. Carcinogenic risk values for lead (0.00057) and chromium (0.00027) also exceeded the USEPA’s acceptable range (1.0 × 10⁻⁶ to 1.0 × 10⁻⁴), indicating a potential lifetime cancer risk. Conclusion: The presence of elevated lead and chromium, along with a critically high WQI, underscores the urgent threat posed by the landfill to groundwater quality and public health. Immediate remediation strategies, consistent groundwater monitoring, and improved waste management practices are essential to prevent long-term health consequences for nearby communities.