Effects of pH on Fluxes of Cadmium in Soils Measured by using Diffusive Gradients in Thin Films

Abstract

The emerging technique of DGT (diffusive gradients in thin films) can be used to measure porewater concentrations and remobilization fluxes of trace metals in soils. This study reports the fluxes from soil solids to solutions in a soil contaminated with different levels of cadmium (Cd) at the naturally acidic pH and after CaCO₃ treatment. The comparison of labile dissolved Cd, determined by using differential pulse anodic stripping voltammetry, and the concentration obtained by DGT shows that pH has little effect on the complexation of Cd in solution and that the effect of liming is more pronounced on the sorption of Cd to the soil particles. The flux from soil to solution seems to be reduced by 10–50 times following liming from pH 5.6 to 7.0. The final concentrations of labile Cd represent 70–95% of the initial labile concentrations and the Cd fluxes varied from 2.8 to 54 µg cm⁻² h⁻¹ at pH = 5.6 and from 0.6 to 5.5 µg cm⁻² h⁻¹at pH = 7.0.

Keywords:

• DGT
• Cadmium
• Contaminated soils
• Liming

Acknowledgments

We thank A. Tessier and R. Goulet for their help with the gels. We also wish to thank the Université de Montréal, the Natural Sciences and Engineering Research Council of Canada and the Metals in the Environment Research Network for their financial support.