Evaluation of Hazard Quotient (Hq) of Toxic and Heavy Metal Concentration in Air Sediments Across Selected Cities in Nigeria

Abstract

<title>Abstract</title> This study evaluates air quality index (HQ) from toxic and heavy metal concentration across selected cities in Nigeria. Gravitational sedimentation method was used to collect air sediments to extract toxic and heavy metals contained in air particulates. Funnel shaped collectors securely attached to clean empty containers were exposed in open spaces at designated locations within the city, for a period of nine months, covering the two major seasons in Nigeria. (January to September, 2023). Airborne particles were allowed to settle naturally in the container along with rainwater. Samples from various points in a city were put together for laboratory analyses. This procedure was repeated in five other cities covering various geographical and climatic regions in Nigeria. The cities include: Benin (S1), Kano (S2), Abuja (S3), Lagos (S4), Enugu (S5), and Calabar (S6). The average concentration of toxic and carcinogenic elements reveals that salinity exhibits the highest HQ at 21.25, followed by nickel (Ni) at 4.58, magnesium (Mg) at 4.43, lead (Pb) at 3.66, chlorine (Cl) at 1.83, and chromium (Cr) at 1.06. Conversely, elements such as; Ar:0.3, NH₃:0.042, Al:0.36, CO:0.02, Cu:0.11, Zn:0.01, K:0.36, NO₂:0.32, NO₃:0.042, Fe:0.31 and Na:0.18 have HQs below 1, indicating safe exposure levels. Cadmium (Cd) displays the highest HQ in Kano (S2) at 2.33, suggesting significant health risks, including cancer and kidney failure. Nickel’s highest HQ is recorded in Edo State, Benin (S1) at 5.5, linked to bronchitis, asthma, and skin irritation. Manganese (Mn) has the highest HQ in Enugu (S5) at 16, with potential for lung inflammation, liver damage, and cognitive impairment. Lead (Pb) shows the highest HQ in Kano (S2) and Calabar (S6) at 8, associated with kidney damage and developmental issues. Salinity’s highest HQ is found in Abuja (S3) at 32.74, impacting water quality and health. Chromium (Cr) exhibits the highest HQ in Kano (S2) at 1.3, potentially causing lung cancer and bronchitis. Potassium (K) exceeds an HQ of 1 only in Kano (S2) at 1.05, posing risks of hyperkalemia and kidney issues. Elements with HQs below 1, including aluminum, cobalt, copper, zinc, nitrite, fluoride, sodium, and conductivity, are deemed safe for human exposure. This study highlights the critical need for monitoring and mitigating exposure to elements with high HQs to protect public health in these urban areas.