| Scope and method of study. Soil properties affect metal solubility and bioavailability to ecological receptors such as plants and soil invertebrates. Understanding the extent to which soil properties modify the bioavailability of metals will provide insight into potential ecological risk. The objective was to examine the relative contribution of pH, organic carbon (OC), cation exchange capacity (CEC), clay, and amorphous Fe and Al oxide (FEAL) to modifying metal bioavailability. The response of lettuce (Lactuca sativa) biological endpoints bioaccumulation, relative dry matter growth (RDMG), and relative germination (RG) to metal-spiked soils were determined. Twenty-one soils were spiked at 300 mg Cd kg -1, 2000 mg Pb kg-1 or 300 mg Zn kg -1. Path analysis (PA) was used to augment traditional regression analysis and provide insight into the relative contribution of each soil property in explaining variation in the dependent variable.; Findings and conclusions. Soil pH ranged from 4.0 to 8.0, OC from 0.50 to 3.0%, CEC from 3.01 to 32.4 cmolc kg -1, clay from 5.0 to 71.3%, and FEAL from 0.009 to 0.195 mol kg-1. In Cd spiked soils, RG ranged from 71.1 to 133%, RDMG from 1.04 to 55.6%, and lettuce tissue Cd from 57.7 to 403 mg Cd kg -1. In Pb-spiked soils, RG ranged from 76.9 to 165%, RDMG from 2.5 to 88.5%, and lettuce tissue Pb from 3.22 to 233 mg Pb kg-1 . In Zn-spiked soils, RG ranged from 87.2 to 190%, RDMG ranged from 3.4 to 85.4% and lettuce tissue Zn from 18.4 to 2038 mg Zn kg-1 . The wide range in lettuce response showed that soil properties strongly modified metal bioavailability. Results of PA showed that the relative importance of soil properties were different for different metals and lettuce endpoints. For lettuce grown in Cd-spiked soils, FEAL and pH explained most of the variation in RDMG and bioaccumulation of Cd. In Pb-spiked soils, most of the variation in RDMG was explained by OC and FEAL and for bioaccumulation by OC and CEC. In Zn-spiked soils, most of the variation in tissue Zn was explained by pH and CEC. |
