Heavy-metal distribution in various types of soil aggregates

Abstract

125 Many regions of the world being heavily polluted, the geochemical cycles of heavy metals in the biosphere are considerably affected by anthropogenic factors. Studies and assessment of environmental pollution with heavy metals have become an integral part of environmental protection problems. In this context, soil is of great interest as a deposition medium [1]. The behavior of heavy metals in soils has been widely studied [2-7], but the consideration of soils in terms of a physical model [8] limited the ability of researchers to elucidate the interactions of heavy metals with soil components. Many heavy metals (zinc, copper, molybdenum, manganese, cobalt, and others) are essential microelements for plants. Recent experimental results [9‐11] indicate that colloidal soil particles reside in the cells of a three-dimensional net of organic humus molecules. The gel structure of the soil can be considered as a humus gel reinforced by colloidal particles. Interacting with water, this reinforced humus gel (RHG) behaves as many polymers; it absorbs water and increases in volume, forming a unified organomineral gel network. This work studies the mechanism of binding of heavy metals by soils, gaining and analyzing data on the heavy-metal distribution in various fractions of soil macroaggregates. Test samples were taken from high-humus horizons of a cultured soddy-podzolic soil from the vicinity of the Klyazma River floodplain, a gray forest soil from Vladimir oblast, and Kursk chernozem. Air-dry soils were sieved into the following fractions (mm): >10, 7‐10, 5‐7, 3‐5, 2‐3, 1‐2, 0.5‐1, 0.25‐0.5, and <0.25. Fractionated samples were pestled in a mortar to particle sizes of less than 1 mm, divided