Metal and metalloid content variation in adjacent urban topsoils: relevance to public health.
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Abstract
Increasing urbanization and industrialization is producing highly contaminated urban topsoils with trace elements which may impact in the morbidity and mortality of the population that live in these urban environments. As a consequence, a comprehensive environmental monitoring study was undertaken in Alcalá de Henares, as it is one of the largest cities in the Madrid Region, Spain. Monitoring of Al, As, Be, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Sn, Ti, Tl, V and Zn in topsoils collected from urban parks from 4 different zones was performed: zone I had a high density of green areas and open spaces, zone II was a more urban environment, with a higher number of buildings; zone III had a higher density of traffic and zone IV is home to industrial activities. Be (p<0.001), Cr (p<0.05), Ni (p<0.01), Sn (p<0.01) and Ti (p<0.05) showed statistically significances between zones. However, these elements also displayed a different pattern in distribution in the soil samples in each zone studied. Thus, zone I was significantly contaminated by Be, Cr and Ti; zone III had significantly higher levels of Cr, Sn and Ti; and zones II and IV had significantly lower levels of all of these metals that showed a dependency on the area of residence. This variation would be a reflection of several sources of these pollutants at the same time, both natural (geological, hydrological, meteorological) and anthropogenic, creating was is called “diffuse pollution” in urban topsoils. Diffuse pollution in urban environments may present a risk for human health as trace element concentrations can vary dramatically between zones even at small distances. Thus, for example, the levels of Be (0.17-2.57 mg kg-1) would require remediation in certain parts of the city as they were higher that the regulatory guidance values for this metal.