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Effect of Soil Modifying Factors on the Bioavailability and Toxicity of Metal Contaminated Soils

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Abstract: Heavy metal and organic chemical contamination of soils is a worldwide problem posing a risk to humans and more directly, soil organisms. Metal toxicity is often not directly related to the total concentration of metals present due to a number of modifying factors that depend, in part, on soil chemical properties. Soil organic matter, pH, and clay content are soil chemical properties that influence metal toxicity and bioavailability. The primary objective of this research was to examine the simple and combined effects of soil physical/chemical parameters (e.g. pH, OM, clay) 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. Earthworm bioassay endpoints included mortality, internal concentration of metal, and cocoon production. The 21 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%). The relationship between all biological endpoints (internal concentrations, mortality, and cocoon production), soil properties (pH, OC, % clay), and soil extractions (Ca(NO3)2-extractable, total, pore water) were determined using simple linear or curvilinear regression. The combined relation between each biological endpoint and soil properties (pH, OC, % clay) were further examined using multiple regression and path analysis. Internal Pb concentrations ranged from 28.7 to 782 mg Pb kg-1, with a mean of 271 mg Pb kg-1. A 27-fold difference in concentration in earthworms exposed to the same total soil content of Pb in 21 soils indicates that soil properties modified the uptake of Pb. There was a strong significant (r = 0.83, P < 0.01) relationship between reproduction and OC but, a less significant correlation (r = 0.52, P < 0.05) between reproduction and pH. Strong correlations between earthworm mortality and Pb extracted by Ca(NO3)2 (r = 0.85, P < 0.01) and pore water (r = 0.81, P < 0.01) were found.

This work has been funded wholly by the United States Environmental Protection Agency. It has been subjected to Agency review and approved for publication.
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Citation:Bradham, K., N. T. Basta, R. P. Lanno, E. A. Dayton, M. Payton, and J. Schroder. Effect of Soil Modifying Factors on the Bioavailability and Toxicity of Metal Contaminated Soils. Presented at Society of Environmental Toxicology and Chemistry, Austin, TX, November 9-13, 2003.
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Contact: Liz Hope - (919) 541-2785 or hope.elizabeth@epa.gov
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Division: Human Exposure & Atmospheric Sciences Division
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Branch: Methods Development & Application Branch
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Product Type: Abstrct/Oral
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Presented: 11/10/2003
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Related Entries:
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Bullet Item EDC Exposure Methods
spacer Relationship Reason:   A Project of the Product
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Last Updated on Monday, October 22, 2007
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