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(P666) Effects of chromium in sediment: 1. Toxicity tests with saltwater field sediments.
Berry, Walter*,1, Boothman, Warren1, Serbst, Jonathan1, Edwards, Philip1, 1 U.S.EPA, Narragansett, RI, USA
ABSTRACT- Chromium exists in sediments primarily in two oxidation states: Cr(III), which is relatively insoluble and nontoxic, and Cr(VI), which 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 AVS concentrations should not contain chromium in the toxic Cr(VI) form. Previous ten day toxicity tests with the amphipod Ampelisca abdita in Cr(VI)-spiked sediments were consistent with this expectation. For example, in sediments where AVS was measurable, chromium concentrations in interstitial water were very low (<100 g/L) and no significant toxicity to A. abdita was observed. In sediments in which AVS was less than 0.1 mole/g, chromium concentrations in interstitial waters increased significantly, with greater than 90% of the chromium in hexavalent form, and mortality of A. abdita was elevated. Mortality based on interstitial water concentrations was consistent with that found in water-only exposures. In this study amphipods were exposed to field-collected sediments from a site contaminated with high concentrations of chromium. Despite the high sediment chromium concentrations in some of the sediments (up to 1,185 g/g), all of the test sediments had measurable AVS, and little or no Cr (VI) in the interstitial water. As expected from the results of the spiked sediment tests, there was little amphipod mortality in any of the sediments and little correlation between sediment chromium concentrations and acute amphipod mortality. These results demonstrate that measurements of AVS and interstitial water chromium can be useful in predicting the lack of acute effects from chromium contamination in sediments.
Key words: chromium, sediment, AVS, interstitial water
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