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(382) Effects of soil properties on the bioavailability and toxicity of metals in contaminated soils to earthworms.
Bradham, Karen*,1, Lanno, Roman2, Basta, Nicholas1, Schroder, Jack1, Payton, Mark1, 1 Oklahoma State University, Stillwater, OK, USA2 Ohio State University, Columbus, OH, USA
ABSTRACT- Due to widespread contamination of terrestrial ecosystems by metals, it is necessary to characterize soils suspected of metal contamination and determine if the metal levels in these soils are a hazard to soil organisms. Ecological soil screening levels based on total metal levels have been suggested for the protection of ecological receptors. However, exposure expressed as total metal levels does not consider the effects of soil physical/chemical parameters on metal bioavailability. The primary objective of this research was to examine the interaction between different combinations of soil modifying factors (pH, organic matter content, cation exchange capacity, clay content) on metal bioavailability. A 28-d toxicity test using Eisenia andrei was conducted to assess the bioavailability of Pb, Cd, Zn, and As spiked individually in field soils. The soils tested had a wide range of chemical properties including soil pH (4.18-8.47), cation exchange capacity (3.0-32.4 cmolc kg-1), organic matter (0.3-3.0%), and clay content (3.8-58.8%). Total metal content and 0.5 M Ca(NO3)2-extractable metal in soils were quantified by ICP-AES. Earthworms were extracted and analyzed for metal content by FAAS, HGAAS, and HG-ICP-AES. Results based on earthworm mortality indicate that metal bioavailability in soils was reduced under conditions of high pH and % organic carbon and increased with reductions these parameters. A positive correlation (r=0.4618) was established for 0.5 M Ca(NO3)2-extractable Cd and earthworm Cd residues (p = 0.003), but there was no relationship observed for the total extractable Cd (EPA 3051) and earthworm Cd residues (p = 0.878). Path analysis and backwards-stepwise regression were used to determine the critical soil modifying factors affecting the bioavailability and toxicity of metals to earthworms. A model of the bioavailability of metals to earthworms was developed using metal availability, extractability, bioaccumulation, and toxicity data.
Key words: bioavailability, metals, ecological risk assessment, soil toxicology
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