| Scope of thesis. The objective of this study was to examine the relationship between soil properties (e.g., pH, organic matter content, clay content) and As, Cd, Pb, and Zn bioavailability and toxicity in earthworms (Eisenia andrei) and develop a mathematical model to describe this relationship.;Findings and conclusions. The range of mortalities observed in this study was the result of differences in metal bioavailability due to metal interactions with the soil properties, assuming similar behavior of earthworms in each soil. Path analysis models proved useful for providing quantitative causal influence of soil properties for Cd, Pb, and Zn, bioavailability and toxicity to earthworms. Overall, pH was the most important soil property modifying the bioavailability and toxicity of Cd, Pb, and Zn. Complete mortality (100%) was observed in soils with Ca(NO3)2-extractable Pb levels >900 mg kg-1. Results show a significant relationship (P < 0.0001) for Ca(NO3)2-extractable Pb and mortality. Regression analysis results established a significant relationship ( P < 0.0001) for 0.5 M Ca(NO3)2-extractable Cd and internal Cd concentrations. Due to Zn regulation by earthworms, a relationship was not found for Ca(NO3)2-extractable Zn and internal concentrations. However, correlation analysis found the relationship between mortality and Ca(NO3)2-extractable Zn concentrations was significant (r = 0.47). A non-significant relationship was found for internal As concentrations and mortality (P = 0.37). Correlation analysis established a significant relationship (P < 0.01) for pore water extractable As and mortality. Biota-soil accumulation factors in this study were deemed as poor indicators of adverse effects of metals. Furthermore, decreasing bioaccumulation factors with increasing available metal concentrations indicate that BSAFs should not be used assess the influence of soil properties on metal bioavailability. The absence of a significant relationship found for internal concentrations and mortality suggests that internal concentrations may not prove useful as indicators of adverse effects of As and Cd toxicity and bioavailability to earthworms. However, a significant relationship was found for internal concentrations and mortality suggesting that internal concentrations may prove useful as indicators of adverse effects of Pb and Zn toxicity and bioavailability to earthworms. |
