Dissolved and colloidal transport of Cd, Pb, and Zn in a silt loam soil affected by atmospheric industrial deposition

As a result of processing of metal ores, trace metals have contaminated lar ge areas of northern France. Metal migration from the soil to groundwater p resents an environmental risk that depends on the physico-chemical properti es of each contaminated soil. Soil water samples were obtained over the cou rse of I year with zero-tension lysimeters from an acidic, loamy, metal con taminated soil. The average trace metal concentrations in the soil water we re high (e.g. for Zn Il mg l(-1) under the surface horizon), but they varie d during the sampling period. Zn concentrations were not correlated with pH or total organic carbon in the solutions but were correlated with Cd conce ntrations. On average, 95% of the Zn and Cd but only 50% of Pb was present in a dissolved form. Analytical transmission electron microscopy was used t o identify the Zn or Pb carriers. Colloids containing Pb and Zn were biocol loids, whereas colloids containing only Zn were smectites. (C) 2001 Elsevie r Science Ltd. All rights reserved.