Cd, Cu and Zn solubility in arable and forest soils: Consequences of land use changes for metal mobility and risk assessment

The effect of land use, total metal content and soil parameters on the distribution of Cd, Zn, and Cu between the solid phase and soil solution is examined in a large field survey. In sifts soil solution samples were obtained by centrifugation of field moist soil samples from six depth layers (0 to 80 cm) in 30 Dutch forest and arable soils. The soils vary in texture, pH, organic matter content, and land use and represent major soil types in the Netherlands. Total metal contents in arable soils exceeded those of forest soils because of manure and fertilizer application and decreased with depth in both land use types, Cd and Zn solution concentrations were higher in forest soils and increased strongly below pH 5.5 despite the low total metal content. Cu solution concentrations were higher in agricultural soils and increased with dissolved organic carbon. Multiple linear regression showed that CEC and pH explained 49% (for Cu), 79% (for Cd), and 83% (for Zn) of the measured variation in distribution coefficients (K(d)). In acid forest soils (pH < 4.5; Zn(total) < 10 mg kg(-1); Cd(total) < 0.3 mg kg(-1)), 80% of all measured Zn and Cd solution concentrations exceeded current ground water quality standards as a result of the high metal solubility at low pH. Taking into account the low acid buffering capacities in these soils, continuous acidification may cause further increase in the soil solution concentration of the metals considered in this paper. (Soil Science 1998;163:859-871).