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BIOAVAILABILITY OF METALS IN ENVIRONMENTAL MEDIA
Citation:
Bradham, K. BIOAVAILABILITY OF METALS IN ENVIRONMENTAL MEDIA. Presented at Science Forum 2003, Washington, DC, May 5-7, 2003.
Impact/Purpose:
To develop faster, lower cost, greener laboratory-based methods with optimum contamination controls and sensitive analytical methods for identified high priority EDCs
Description:
Heavy metal and organic chemical contamination of soils is a worldwide problem posing a risk to humans and more directly, soil organisms. Due to widespread metal contamination, it is necessary to characterize soils suspected of metal contamination and determine if the metal levels in these soils pose a hazard. 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. Bioavailability is a measure of the potential for entry of a metal into biological receptors. It is specific to the receptor, the route of entry, duration of exposure, and the exposure matrix. Risk is directly related to metal bioavailability, which depends upon metal concentration, the geochemical forms of metal, the species of organism exposed, physical and chemical characteristics of the exposure environment, and the exposure duration. In order to understand metal bioavailability in soils, chemical and biological techniques are needed to measure the portion of metal that is theoretically bioavailable to humans and soil organisms. These can range from direct measures of bioavailability such as concentrations in soil organisms to indirect measures such as chemical extractions. Current routine practices of investigating the nature and extent of contamination at metal-contaminated sites involve determining total metal content in soils. The quantity of metal to be used as exposure concentrations in the risk calculation is an assumed percentage of the total content, which may be bioavailable. Often, very high percentages (near 100%) of total metals are assumed bioavailable. While this assumption is conservative in terms of being protective of human health and the environment, it may not be a reasonable estimate of site conditions because the actual bioavailability of metals has not been assessed. The resulting risk may overestimate the true risk of exposure to site media. Overestimation of risk may result in lengthy and costly site remediation that may not be warranted.