Cerqueira, B.;Covelo, E. F.;Andrade, M. L.;Vega, F. A.

Department of Plant Biology and Soil Science, University of Vigo, 36310 Vigo (Spain)

a horizons;agricultural chemicals;b horizons;bioavailability;cambisols;capacity;cation exchange;cation exchange capacity;copper;desorption;heavy metals;horizons;hysteresis;indexes;lead;luvisols;manganese;metals;movement;organic matter;polluted soils;pollution;properties;retention;soil;soil properties;soil science;soil types (anthropogenic);soil types (genetic);sorption;vermiculite;agrochemicals;anthropogenic soil types;environmental pollution;genetic soil types;mn;soil horizons;sols lessives

The mobility and bioavailability of heavy metals in soils is largely governed by sorption and desorption phenomena. Cu²⁺ and Pb²⁺ are among the most potentially toxic heavy metals and they are present, often concomitantly, in many polluting spills and in agrochemicals. The objective was to assess and compare the competitive sorption and desorption capacities and sorption hysteresis of Cu²⁺ and Pb²⁺, as well as their migration through the profiles of four natural soils: a Humic Umbrisol, an Umbric Cambisol, an Endoleptic Luvisol and a Humic Cambisol. In all horizons Pb²⁺ was invariably sorbed and retained to a greater extent than Cu²⁺. The sorption and retention of Cu²⁺ were most influenced by pH, effective cation exchange capacity (CECe) and Mn oxide content. On the other hand, the fixation capacity of Pb²⁺ was most influenced by pH, CECe, and Mn oxide and organic matter contents. pH and CECe were the individual soil properties most markedly influencing Cu²⁺ and Pb²⁺ sorption and retention. In all the horizons Pb²⁺ exhibited greater hysteresis than Cu²⁺. In each soil the hysteresis in the A horizon was greater than that in the B horizon, except in the Bt horizon of the Endoleptic Luvisol, due to its high pH and vermiculite content. Based on migration indices, Pb²⁺ was less mobile than Cu²⁺ in the studied soils.