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PREDICTING THE TOXICITY OF CHROMIUM-SPIKED SEDIMENTS USING ACID VOLATILE SULFIDE AND INTERSTITAL WATER MEASUREMENTS
Citation:
Boothman, W S., W J. Berry, J R. Serbst, AND P A. Edwards. PREDICTING THE TOXICITY OF CHROMIUM-SPIKED SEDIMENTS USING ACID VOLATILE SULFIDE AND INTERSTITAL WATER MEASUREMENTS. Presented at Society of Environmental Toxicology and Chemistry Conference, Philadelphia PA, November 14-18, 1999.
Description:
Chromium exists in sediments in two oxidation states: Cr(III) is relatively insoluble and nontoxic, whereas Cr(VI) is much more soluble and toxic. Cr(VI) is not thermodynamically favored in anoxic sediments. Acid-volatile sulfide (A VS) is formed only in anoxic sediments, therefore, sediments with measurable amounts of A VS should not contain chromium in its toxic form. Ten day toxicity tests with the amphipod Ampelisca abdita were conducted using a sandy sediment with low A VS <2 mmole/g) and a silty sediment with higher A VS (~10 mmole/g). Both sediments were spiked with Cr(VI) to achieve nominal metal:AVS ratios of 0.215 to 10. Toxicity to A.abdita of both total and hexavalent chromium was also determined in water-only exposures. Interstitial and overlying waters and simultaneously extracted metals (SEM) were analyzed for total chromium; hexavalent chromium was also determined by an iron oxyhydroxide coprecipitation method. AVS decreased and total chromium in SEM increased proportionally with added Cr(VI). In sediments where A VS was present, chromium concentrations in interstitial water were very low <100 mg/L), no Cr(VI) was measured in the SEM fraction, i.e. chromium was entirely reduced to Cr(III), and no significant toxicity to A.abdita was observed. Only in sediments in which SEM exceeded A VS were chromium concentrations in interstitial waters significantly increased, with greater than 90% of the chromium in hexavalent form. In these sediments AVS decreased to less than 0.1 mmole/g and mortality of A.abdita was high. Mortality based on interstitial water concentrations was consistent with that found in water-only exposures. These results demonstrate that measurements of A VS and of chromium in interstitial water can be useful in assessing risks of chromium contamination in sediments.