Evaluation of hazard quotient (HQ) of toxic and heavy metal concentration in air sediments across selected cities in Nigeria

This study evaluates Hazard Quotient (HQ) from toxic and heavy metal concentration across selected cities in Nigeria. The gravitational sedimentation method was used to collect air sediments to extract toxic and heavy metals contained in air particulates.  Funnel shaped collectors which were securely attached to clean empty containers were exposed in open spaces at designated locations within the city, for a period of nine months (January to September 2023), covering the two major seasons in Nigeria. Airborne particles were allowed to settle naturally in the container along with rainwater. Samples from various sub-locations within the city were put together for spectroscopic analyses. This procedure was repeated in six 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; lead (Pb) at 5.66, nickel (Ni) at 4.58, magnesium (Mn) at 4.43, Cadmium (Cd) at 1.83, Iron (Fe) at 1.31 and chromium (Cr) at 1.06. Conversely, elements such as; (NH₃) :0.042, (Al):0.36, (Co):0.02, (Cu):0.11, (Zn):0.01, (K):0.86, (N):0.32, (N):0.042, (F):0.12 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, which may include cancer and kidney failure. Nickel has highest HQ 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. 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.  This study highlights the critical need for monitoring and mitigating exposure to elements with high HQs to protect public health in these urban areas.