Hidden hazards in urban soils: A meta-analysis review of global heavy metal contamination (2010-2022), sources and its Ecological and health consequences

This study evaluated data from the literature on the presence of heavy metals for the period of 2010–2022 in the soils of 174 cities across the world. The range values (mg/kg) of Arsenic (As), lead (Pb), mercury (Hg), cadmium (Cd), chromium (Cr), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn) and iron (Fe) were 0.95–152.00, 2.27–5780.00, 0.05–178.19, 0.03–298.90, 1.10–1631.43, 0.41–2560.00, 2.08 12,986.00, 1.14–3420.00 and 28.10 88,531.00. With the exception of Cr and Fe, all metals' average concentrations were higher than their average crustal values. A low to extremely high degree of contamination, presumably impacted by Pb, Hg, and Cd, was shown by the pollution indices. Urbanization, and industrial exhausts, are the main causes of high levels of pollution. Ecological risk showed that metals in urban soils pose a slight to highest environmental risk with mercury and Cd pose the highest ecological risk. A health risk assessment showed that some of the cities' residents are at risk for non-carcinogenic health risks (HI > 1), which are brought on by oral consumption and skin contact with metals in the soil. Inhabitants of these cities are exposed to carcinogenic health risk (HI > 1 × 10−4) which are triggered by ingestion and contact with heavy metals in soils. Therefore, frequent monitoring of heavy metals in urban soils should be carried out to forestall the environmental and health risks associated with them which is the main goal of this review.