Potentially toxic elements in urban soil catenas of W-Mo (Zakamensk,Russia) and Cu-Mo (Erdenet,Mongolia) mining areas

Purpose

The aim of this study was to characterize the conditions of the lateral migration of potentially toxic elements (PTEs) and to identify the zones of their accumulation in soil catenas of ore-mining landscapes in the cities of Zakamensk (Buryat Republic, Russia) and Erdenet (Mongolia) which are situated in the basin of the Selenga River.

Materials and methods

Eight soil catenas across the river valley with 31 pits in Zakamensk area and five catenas with 15 pits in Erdenet area were studied. Soil samples were collected in four landscape–geochemical positions: autonomous, on tops of the hills; trans-eluvial, on slopes of river valleys; trans-accumulative, at the footslopes; and superaqual, on the river floodplains. The total contents of 16 PTEs in the 148 samples were determined by mass spectrometry and by atomic emission spectrometry with inductively coupled plasma.

Results and discussion

It is found that the chemical composition of undisturbed soils is greatly affected by the widespread distribution of volcanic rocks enriched with W, Mo, Cd, Bi, and Sr in Zakamensk and with V, Co, Sr, and As in Erdenet. The difference between geochemical positions is relatively small. Under the influence of technogenic loads in the cities, the concentrations of PTE change along soil catenas increases by an order of magnitude. For chalcophile elements—Mo, Bi, Pb, Sb, and Cu in Zakamensk and Cu, Zn, Mo, Cd, Sn, and W in Erdenet—the type of their lateral distribution in the soil catenas changes because of the intense migration from the tailings and facilities with water and air flows. The accumulation of PTEs takes place on the chemisorptive (V, Co, Ba, As, Cr, and Ni), gley (Mo and Sb), organomineral (Sn), and alkaline (Sr and W) lateral geochemical barriers (LGBs) confined to subordinate positions. The artificial technological LGBs are formed due to the increased content of sand derived from the tailings by water erosion in Zakamensk and the input of silt particles windblown from the technogenic sources in Erdenet. This causes the rise in the concentrations of major ore elements (Mo, W, and Cu) and the accompanying elements (Pb, Bi, As, Sr, Cr, and Ni).

Conclusions

The results of soil–geochemical studies using the catenary approach and concept of LGBs made it possible to understand the main features of migration and fixation of PTEs in soils of the mining centers. They indicate the formation of a system of LGBs with intensive accumulation of major ore elements and associated ones in the subordinate landscapes of Zakamensk and Erdenet.