Abstract
The influence of urban structures and land use patterns of metropolitan cities on the distribution of contaminants is not well understood. In this study, two metropolitan cities [Jeddah (a typical corridor city) and Madinah (a typical compact city)], featuring different spreading patterns and urban structures, were selected to investigate the contamination level and potential risk caused by metals (i.e., Pb, Zn, Co, Fe, Al, Cr, Cu, Ni, and Mn) associated with urban dust. The findings of this study show that a metropolitan city with a limited variety of activities and a polar center (e.g., Madinah) displays a typical distribution pattern of metals, i.e., concentrations of metals increase gradually toward the center of the city. In contrast, a metropolitan city with multiple major activities (e.g., Jeddah) displays a different distribution pattern, controlled by multiple key actors (e.g., seaports, oil refineries, and desalination/power plants) able to shift the location of highest contamination away from the city center. The above findings are supported by the results of several contamination and health indices. In Jeddah, the highest Pb contamination was found near an oil refinery based on geoaccumulation index (Igeo), contamination factor (CF), enrichment factor (EF), and ecological risk (Ei) values; whereas, the highest Zn contamination was found near a seaport, based on EF, CF, and Ei values. However, in Madinah, the contamination indices indicate that the most contaminated locations are near the city center. The highest non-carcinogenic health risk in Jeddah was found near an oil refinery and in the city center; whereas in Madinah, it was found mainly in the city center. Although there is no significant risk of cancer due to metals associated with dust in the two cities, Cr, representing a health risk contribution of >24%, was the major contributor of non-carcinogenic health risk in the two metropolitan cities.
Highlights
The risk of human exposure to metals threatens public health, as they can cause multiple adverse health effects[1,2]
A typical pattern of compact city, where the concentrations of selected metals, namely Pb and Zn, increase toward the center, was observed in Madinah, whereas a corridor city pattern, where metal contamination was derived away from the city center, was observed in Jeddah. Various factors such as oil refineries, seaports, desalination/ power plants, and industrial areas play a major role in metals accumulating in sites away from the city center, as demonstrated by the results of several contamination indices and the ecological risk index for Jeddah
For Madinah, the three composite indices of metals (NPI, Pollution load index (PLI), and risk index (RI)) were unanimous in that the sampling locations in the city center were the most contaminated; whereas for Jeddah, the most contaminated sites were those near the main activities of the city and in the city center
Summary
The risk of human exposure to metals threatens public health, as they can cause multiple adverse health effects[1,2]. The biological processes of plants are heavily affected by Cr toxicity[4] Some metals, such as lead (Pb) and aluminum (Al), are nonessential, with no known beneficial effects for living organisms[3]. Pb is classified by the IARC as possibly carcinogenic to humans (Group B2 category), and chronic exposure to Pb causes infertility, paralysis, mental retardation, brain and kidney damage, and other health problems[1,4]. Metals are generated from a wide range of anthropogenic and natural sources, including weathering of the Earth’s crust, industrialization, and mining[2]; in urban areas, heavy traffic is considered a major source of metals[5]. The arrangement and relationships of the arrays of services, goods, and www.nature.com/scientificreports/
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