CD, CU AND ZN SOLUBILITY IN ARABLE AND FOREST SOILS - CONSEQUENCES OFLAND-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 solut ion is examined in a large field survey. In sifts soil solution sample s 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 so ils vary in texture, pH, organic matter content, and land use and repr esent major soil types in the Netherlands. Total metal contents in ara ble soils exceeded those of forest soils because of manure and fertili zer application and decreased with depth in both land use types, Cd an d Zn solution concentrations were higher in forest soils and increased strongly below pH 5.5 despite the low total metal content. Cu solutio n concentrations were higher in agricultural soils and increased with dissolved organic carbon. Multiple linear regression showed that CEC a nd pH explained 49% (for Cu), 79% (for Cd), and 83% (for Zn) of the me asured variation in distribution coefficients (K-d). In acid forest so ils (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 gr ound water quality standards as a result of the high metal solubility at low pH. Taking into account the low acid buffering capacities in th ese soils, continuous acidification may cause further increase in the soil solution concentration of the metals considered in this paper. (S oil Science 1998;163:859-871).