Assessment of Current Risks of Excessive Heavy Metal Accumulation in Soils Based on the Concept of Critical Loads: A Review

Abstract

Abstract At the international level, the concept of critical loads developed under the Convention on Long-Range Transboundary Air Pollution directed by the United Nations Economic Commission for Europe is actively used to assess the risks of excessive inputs of pollutants into ecosystems. The review considers the main principles of the concept of critical loads and methods of its application for assessing the current risks of excessive accumulation of heavy metals (HMs) in soil as a component of terrestrial ecosystems from the standpoint of ecotoxicological effects (on plants, soil invertebrates, and microorganisms). Under this concept, the critical concentrations of Cd, Pb, Cu, and Zn for soils are for the first time estimated using the functions of critical concentrations taking into account the properties of soils (primarily, acidity and the contents of organic matter and clay). The main attention is paid to the rationale and development of the models for assessment of the critical concentrations and transfer functions connecting the concentrations of HM compounds in soils and soil solutions. The current environmental risks of excessive HM accumulation are assessed by comparing them with their critical concentrations. Current challenges and future prospects for analyzing the current environmental risks based on the concept of critical loads include the reduction in the uncertainty of estimates, combined effect of different metals in a multicomponent pollution, field validation of processes and modeling results, and the impacts of climate change and land use.