Influence of human impacts on trace metal accumulation in soils of two Hungarian cities

Highlights: • Urban soils are frequently contaminated with plant available trace metals. • Soils of two medium-sized cities are investigated and compared. • Cd, Co and Ni content did not exceed natural background concentration. • Cu, Pb and Zn exceed pollution limit on several sampling sites. • Despite the expectations, extreme values appeared in the suburbs of both cities. Despite the advanced activity of urban soil research, comparison of available trace metal contents in the soil of settlements has not yet been well investigated. First aim of research was the comparison of human impacts on urban soils in two Hungarian cities with different structure and development. To detect the sources of contamination, Szombathely and Sopron cities were separated into urban, suburban and peri-urban areas. Altogether 192 topsoil samples were collected at 0–20 cm in order to measure the physicochemical properties of the soil. Instead of total element contents, plant-available trace metal concentrations – Cd, Co, Cu, Ni, Pb, Zn – were determined using ICP-OES method. Due to different geological conditions, urban soils of the investigated settlements had similar properties in the case of pH, CaCO₃ and texture. In the case of plant available trace metals, limit excesses were found in urban and peri-urban areas mostly, but high values were recorded in the suburb. The amount of Cd_available, Co_available and Ni_available were negligible. Downtown area was the most contaminated in both cities, but extremes appeared in suburban areas. In Szombathely, Cu_available values were <40 mg Cu/kg, but extremely high Cu_available results were found in the peri-urban viticulture areas of Sopron (>90 mg Cu/kg). The samples taken alongside busy roads near the city centre were Pb_available-contaminated due to traffic. The Pb_available concentration decreased slightly towards the suburban areas of the cities. The Zn_available level exceeded 40 mg Zn/kg in soils taken from the watercourses of Szombathely. The highest trace metal pollution levels were recorded in soils of public parks of Sopron. Urban soils of Szombathely were more homogenized than urban soils of Sopron. Based on statistical analyses and comparison of the relations of urban, suburban, and peri-urban areas of Sopron to Szombathely, Szombathely's urban soils show more homogeneity.