Mobility of heavy metals as related to soil chemical and mineralogical characteristics of Brazilian soils

In order to better understand the relationship between soil characteristics and mobility of some heavy metals, correlation studies were conducted in s amples of unlimed and limed A, B and C horizons of three Brazilian soils, r epresentative of the majority of the-tropical soils. A number of chemical a nd mineralogical characteristics of one Oxisol and two Ultisols were relate d to the retardation factors (R-f) for zinc (Zn), cadmium (Cd), copper (Cu) and lead (Pb). The retardation factors, obtained in leaching column experi ments, were used as an estimate of solute movement in the profile. Soil typ es and soil horizons were found to influence metal retardation factors whic h, in turn, correlated better with the chemical than the mineralogical soil characteristics. For the unlimed soil samples, the soil characteristics th at significantly correlated with Zn-R-f and Cd-R-f were the sum of exchange able bases (SB), and soil exchangeable (Ca-KCl) and non-exchangeable (Ca-HC l) calcium contents. These results showed the strong influence of the catio n exchange phenomenon on the retention and mobility of these two metals. Fo r Cu and Pb, not only SB, cation exchange capacity (CEC) and Ca-KCl and Ca- HCl but also the organic matter correlated well with the R-f, showing that complex or chelate formation may play an important role in the movement of these elements. The important soil chemical characteristics related to the retardation factors in the limed soil samples were SB for Cd, and Ca-HCl fo r Cu and Pb, suggesting that precipitation may also influence the mobility and retention of the latter two heavy metals in these soil samples. Soil pH influenced the heavy metals adsorption and movement as shown by the signif icant correlation with the retardation factors when the combined data for t he unlimed and limed soil samples was considered. (C) 2000 Elsevier Science Ltd. All rights reserved.