Specificities of considering migration capability of heavy metals in assessing ecological hazard of polluting soils of urban ecosystems

Abstract

Necessity of assessing how badly are soils of urban ecosystems polluted by heavy metals has been motivated by the growth of technogenic load and awareness of the hazard level. The study aimed to identify and justify the use of an indicator to assess the actual environmental risks of soil contamination with heavy metals in urban ecosystems. This indicator eliminates the influence of soil buffering capacity on metal fixation and considers the migration potential under specific conditions of spatial pollution distribution. The studies were conducted within the urban ecosystem of Dnipro city (Ukraine) – a powerful center of metallurgy, machine-building, metal-processing industries, and rocket-space construction. In this work, the gross content and mobile forms of the following five heavy metals were studied: Cu, Zn, Pb, Cd, and Ni. The assessment of pollution intensity was carried out using the Nemerov pollution index (NPI) for the gross content and mobile forms in order to reveal the level of ecological hazard caused by the growth of heavy metals in soil. It was ascertained that by the level of ecological hazard, the pollution intensity of heavy metals in soils of the urban ecosystem of Dnipro city can be represented as the following inequality sequence: Zn ˃ Pb = Cu ˃ Cd ˃ Ni. The migration capability of heavy metals is conditioned by an increment of their gross content, whereas the city soil is losing its buffer property. A tendency of the NPI growth is revealed within the gross content to potentially mobile forms as a result of considering the migration capability of heavy metals. The NPI application efficiency is substantiated to take into account specificities of how urban ecosystems are formed and function, including variety and spatial propagation of pollution by heavy metals, as well as their migration capability.