Heavy metal translocation in soil-plant system in conditions of urban anthropogenic pollution (Tyumen, Russian Federation)

Soil contamination by heavy metals causes metal accumulation by plants, which leads to the degradation of plants communities and migration of toxicants with food chains to man. Therefore, the investigation of heavy metal concentration in soils of urban areas is an urgent scientific task. This study aims to examine the translocation of heavy metals from urban soils to herbs in Tyumen (Russian Federation).  Soil surface layer was collected at control site, near the highway as well as from areas with metallurgical, motor building, oil refinery and battery manufactory plants in Tyumen. Meadow grass, red clover, wild vetch, chamomile and coltsfoot were collected at all examined sites.  The mobile and acid-soluble heavy metal fractions in soils, as well as the heavy metal contents in plants, were determined by atomic absorption spectrophotometry. The bioconcentration factor was estimated as the ratio of the amount of heavy metals in soils to that in plants. The study was performed during three-year period from 2017 to 2019. Heavy metal concentrations in urban soils were higher than those at the control site by 20% and by up to 10 times. The greatest heavy metal accumulation in both soils and plants was found at the battery manufacturing and metallurgical plants, exceeding the control levels of Pb and Fe by 2-17 times. The Cu, Fe and Mn contents in soil were positively correlated with those in plants. Heavy metal translocation by the plants was species-specific. The percentages of the mobile heavy metal fractions decreased in the following order: Mn>Zn>Cu>Fe. Heavy metal accumulation in plants in the urban sites compared to that at the control site decreased in the following order: Fe>Zn>Cu>Mn>Pb>Cd. Coltsfoot exhibited the highest Fe, Mn, and Zn accumulation, which exceeded the control levels by 17, 5, and 3.5 times, respectively. The heavy metal bioconcentration factors, indicators of translocation, decreased in the following order: Cu>Zn>Cd>Pb>Mn>Fe. The heavy metal translocation suggests the need to relocate industrial facilities to outside the city. Future monitoring of the study area is needed to ensure its long-term ecological safety.