Monday, November 13, 2006

Bioaccessibility of Trace Elements in Coals.

Edward Landa1, Kathryn Conko1, and Allan Kolker2. (1) US Geological Survey, MS 430, 12201 Sunrise Valley Dr, Reston, VA 20192, (2) US Geological Survey, MS 956, 12201 Sunrise Valley Dr., Reston, VA 20192

Particulate coal can enter soils and sediments at or near former or active mining sites by direct mixing, or fluvial and aerial deposition. The same environmental processes can cause soil contamination at industrial sites that used coal as a fuel (power plants, or other boilers or furnaces), or as a reagent feedstock (e.g., coke-, oil- or gas-production from coal). The occurrence of such raw (non-combusted) particulate coal as a contaminant phase in soils and sediments has received only limited attention. Trace element constituents of particulate coal have the potential to enter the human food chain when soil is ingested by grazing animals, as well as by direct human ingestion of soil. Where coal is the host phase of metals in such soils, knowledge of its bioaccessibility is important in assessing potential bioavailability and risk. With this in mind, we have examined the bioaccessibility of selected trace elements (Al, As, B, Ba, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V, and Zn) on a suite of 22 coal samples from the Donbas region of Ukraine using sequential extraction with simulated gastric and intestinal fluids. For selected coals, we saw high bioavailable inventories of toxic elements; for example, in a set of samples (from one mine) with elevated As contents (126-268 ppm total As; about 10-20 times typical crustal abundance), from 3 to 29 %  of the As was extracted in the gastric digest.