Geospatial patterns and geochemical compositional characteristics of molybdenum in different mediums of an urban environment

Abstract

Urban areas are characterized by the presence of certain potentially toxic elements including molybdenum (Mo). Therefore, compositional data analysis combined with geospatial mapping was applied in this study to reveal the spatial distribution characteristics of Mo in courtyard surface dust (dust), soils, and river sediments (sediments), to identify potential sources of Mo, and to reveal Mo geochemical associations in different urban environmental mediums. The mean contents of Mo decreased in the following order: dust (11.9 mg/kg) - soil (5.84 mg/kg) - sediment (4.87 mg/kg). The highest maximum Mo content among the studied mediums (61.8 mg/kg) was detected in dust. It was the only investigated medium where a very high level of Mo enrichment was observed (4.4% of samples). Moreover, a significant level of enrichment predominated in dust (47% of samples) whereas in soil, moderate enrichment prevails (68.5%). A significant correlation of Mo contents was observed with Zn contents in all the studied mediums, and with Ca contents in soil and sediments. A significant negative correlation was observed only between Mo contents in dust and sampling site altitudes suggesting that high-rise buildings might play the role of geochemical barriers. Principal component analysis, k-means and hierarchical clustering showed that in the geogenic elements soil group Mo showed an affinity to be bound by Fe/Mn oxide/hydroxides whereas the Mo coprecipitation, complexation and absorption by carbonates predominated in the Mo-related soil group (geochemical compositional association of Mo, Zn, Cu, Pb, and Ca) under anthropogenic influence. For dust, the geochemical compositional association was the same, but in the geogenic-related group, Cu was the most closely associated element instead of Zn. The spatial location of the Mo-related group of samples identified by k-means clustering indicates that Mo concentrate processing plant may be a potential source of Mo introduction into the urban environment.

Keywords: Molybdenum; River sediments; Soil; Source identification; Surface dust; Urban environment.