Assessing bioaccessible fractions of arsenic, chromium, lead, selenium and zinc in coal fly ashes

The utility of a physiologically based extraction test for evaluating the bioaccessibility of metals from fly ash in the human gastrointestinal system was evaluated in the present research. Calcium-rich and silica-rich fly ashes collected from eight power plants in India and United States of America were assessed for bioaccessibility for arsenic, chromium, lead, selenium and zinc. The results from the physiologically based extraction test were compared with those from a sequential extraction procedure that is often applied to solid wastes. Based on the physiologically based extraction test results, more than 40 % of the arsenic was found to be bioaccessible for all the ashes while selenium was very accessible for the calcium-rich ashes. Lead was found to be insignificantly bioaccessible in calcium-rich as well as silica-rich fly ashes. The mobilization of metals in the first three steps of the sequential extraction procedure was similar to the mobilization in the physiologically based extraction test for selenium for all ashes and for arsenic and chromium for most ashes, but the sequential extraction procedure mobilized more zinc than did the physiologically based extraction test. These results indicate that while sequential extraction procedures can provide good estimates of the bioaccessibility of many elements, extraction tests that more closely simulate physiological conditions can provide more accurate measures of bioaccessible concentrations of metals.