Concentrations of selected trace elements in surface soils near crossroads in the city of Bratislava (the Slovak Republic)

It is well known that road transport emits various trace elements into the environment, which are deposited in soils in the vicinity of roads, so-called roadside soils, and thus contributes to the deterioration of their chemical state. The aim of this work was to determine concentrations of some metals and metalloids (arsenic (As), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), antimony (Sb), vanadium (V), and zinc (Zn)) in soils from crossroads with traffic signals, which are characterized by deceleration of vehicles and increased emissions of elements related mainly to brake and tyre wear. The results confirmed a moderate enrichment of soils with Cu, Pb, and Zn (enrichment factor (EF) values > 2) and significant enrichment for Sb (EF > 5), while the other elements showed no or minimal enrichment. The age of crossroads proved to have a positive influence on the accumulation of some elements in soils with the largest differences for Cu, Fe, Pb, Sb, and Zn (p < 0.001). Traffic volumes expressed as the average daily traffic intensity (ADTI) also positively influenced soil concentrations of Cr, Cu, Pb, Sb, and Zn, while distance to the crossroad had a significant negative effect on the soil concentration of Cu, Sb, and Zn (p < 0.001). The stable isotopic ratios of Pb, ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb, ranging from 1.1414 to 1.2046 and from 2.0375 to 2.1246, respectively, pointed to the mixed natural-anthropic origin of Pb in the soils of crossroads with a visible contribution of traffic-related sources. Based on the above findings combined with covariance among the studied elements using statistical methods applied to compositionally transformed data, it was possible to show that Cu, Pb, Sb, and Zn clearly originated from road traffic.