| Scope and method of study. There are two chapters in this thesis. The purpose of the first chapter was to assess bioavailability, phytotoxicity and bioaccumulation of As, Cd, Pb and Zn to ryegrass, Japanese millet and alfalfa based on their 0.1 M Ca(NO3) 2 extraction. Effect of soil properties (e.g., pH, organic matter content, clay content) on the bioavailability, phytotoxicity and bioaccumulation of As, Cd, Pb and Zn to ryegrass, Japanese millet and alfalfa was also evaluated. The purposes of the second chapter were (1) evaluate the effect of the wet-dry cycles on the availability of metals (As, Cd, Pb and Zn in this study); (2) evaluate the effect of spiking temperature on the availability of metals (As, Cd, Pb and Zn); (3) compare the constant and variable metal availability on the assumption that the metal exposure was constant and variable during the earthworm and plant bioassay after spiking, respectively.; Findings and conclusions. According to the first study, plants yield decreased with decreasing soil pH and increased with increasing soil clay and OC content. Extractable Cd, Pb and Zn may be used to assess EC20 and EC50 of the plants tested. Extractable Pb may be used to assess their bioavailability and bioaccumulation to the three plants tested. However, relationships between extractable Zn, Cd, As and their bioavailability and bioaccumulation to the plants require further investigation. According to the second study, the effects of the spiking temperature on the metal availabilities were different among the metals, soils and wet-dry cycles. Three wet-dry cycles were recommended regardless of the type of metals and incubation temperatures. The availabilities of the studied metals should be measured periodically during bioassays and the metal exposure should be calculated based on the periodical measurements. |
