Effects of acid rain on competitive releases of Cd, Cu, and Zn from two natural soils and two contaminated soils in hunan, China

Abstract

Leaching experiments of rebuilt soil columns with two simulated acid rain solutions (pH 4.6– 3.8) were conducted for two natural soils and two artificial contaminated soils from Hunan, southcentralChina, to study effects of acid rain on competitive releases of soil Cd, Cu, and Zn. Distilled water was used in comparison. The results showed that the total releases were Zn>Cu>Cd for the natural soils and Cd>Zn≫Cu for the contaminated soils, which reflected sensitivity of these metals to acid rain. Leached with different acid rain, about 26–76% of external Cd and 11–68% external Zn were released,but more than 99% of external Cu was adsorbed by the soils, and therefore Cu had a different sorption and desosption pattern from Cd and Zn. Metal releases were obviously correlated with releases of TOC in the leachates, witch could be described as an exponential equation.Compared with the natural soils,acid rain not only led to changes in total metal contents, but also in metal fraction distributions in the contaminated soils. More acidifed soils had a lower sorption capaity to metals, mostlt related to soil properties such as pH organic matter, soil particles, adsorbed SO42-, exchangeable AI3+ and H+, and contents of Fe2O3 and AI2O3.