Hazardous Heavy Metals in Urban Cemetery Soils: Health Risk Assessment of Vegetable Cultivation in Benin City

Abstract

In this research, we examined the amounts of heavy metals in both vegetables and soil samples, and the potential health risks associated with consuming vegetables sourced from the vicinity of Second cemetery, Benin City, Edo State, Nigeria. Soil samples, were collected using a hand auger from depths of 0 to 20cm, air-dried, crushed to powder and sieved to obtain fine particles. Simultaneously, four distinct vegetables (mango, orange, potato, and bitter-leaf) were randomly gathered from the areas surrounding the cemetery, and taken to the Civil Engineering Laboratory at the University of Benin, Benin City, Nigeria, for further preparation. After washing with distilled water to remove dirt, they were separated, air-dried, and further dried in an oven at 65°C for 72 hours until a constant weight of 5g was obtained. Subsequently, the dried leaves were pulverized with a mortar and pestle, converted to powder, and stored in a plastic bag for subsequent analysis. The analysis of the collected vegetable samples involved employing a wavelength-dispersive X-ray fluorescence spectrometer (SKYRAY INSTRUMENT EDX3600B). Health risk parameters such as Health Risk Index and Target Health Quotient, were assessed. The results obtained disclosed that the soils and plants are contaminated with Sn, Sb, Fe, Pb, Cd, and Zn. The Target Health Quotient (THQ) values reached 74.606, surpassing the WHO-recommended limit of one, suggesting that the ingestion of these vegetables poses significant health risks to humans, with children being the most vulnerable due to their susceptibility to heavy metals toxicity.