Water-erosion transport of heavy metals from contaminated soils

摘要

The objective of this paper is to describe the initial stage of trace element partitioning between liquid and solid phase as a result of interactions of surface water with erosion washing: its finest particles form suspended material drifted by streams. Laboratory experiments were conducted to determine the partitioning pattern of some toxic trace elements (As, Cd, Cu, Ni, Pb, Zn) between solution and solid phase of washing and to study the effect of some system parameters on this process. Experimental materials involved a fine fraction of extremely contaminated soils obtained by use of a portable rainfall simulator, natural washing from uncontaminated soil in which interactions with model solutions containing elevated concentrations of heavy metals were examined. Washings from heavily contaminated soils are a great load of surface streams. A sudden change in environmental conditions in surface waters (pH, concentrations of dissolved forms of elements, suspension density) is accompanied by very rapid processes of element repartitioning between liquid and solid phase. Following the applications of contaminated rainfall water, 70–90 percent of heavy metals were absorbed by the solid fraction of washing. The highest quantities of lead and cadmiumwere fixated. Approximately the same percent of nickel and zinc were fixated, and their absorption was related to soil type to a larger extent than in the former two elements. An equilibrium was established more slowly in soils with higher saturation, the resultant percent of an absorbed element was higher and the liquid fraction of washing was not contaminated. The content of elements released to solution from fractions of finer texture was much higher than in coarser fractions. Particularly in the conditions of this country where a majority of water sources are rainfed, the quality of these sources will be more and more influenced by matters washed away from the soil surface. It is apparent from this perspective that these problems should be studied,their possible extent and causes should be determined, searching for preventive protective measures. The knowledge will contribute to specification of the basic data applied to improvement of protective technologies that reduce the contamination of surface water sources by erosion products. Benefits will be seen not only in the sector of agriculture but also in water management. The results published in this project will be a basic material for applied research, particularly focused on minimization ofthe penetration of extraneous matters into food chain, including water.