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PREDICTING THE TOXICITY OF CHROMIUM-SPIKED SEDIMENTS USING ACID-VOLATILE SULFIDE AND INTERSTITIAL 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 INTERSTITIAL WATER MEASUREMENTS. Presented at North Atlantic Chapter of the Society of Environmental Toxicology and Chemistry, Newport, RI, April 14-15, 2000.
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 (AVS) is formed only in anoxic sediments, therefore, sediments with measurable amounts of AVS 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 AVS <2 ,mmole/g) and a silty sediment with higher AVS ( ~ 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 AVS 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 AVS 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 AVS and of chromium in interstitial water can be useful in assessing risks of chromium contamination in sediments.