In Chesapeake Bay, Maryland, USA, some of the most contaminated sediments are found in the highly industrialized Baltimore Harbor-Patapsco River area. As part of a comprehensive assessment of sediment quality in this system, sediment toxicity was assessed in 10-d acute tests with the estuarine amphipod Leptocheirus plumulosus. Mean amphipod survival was significantly reduced in 7 of the 25 samples tested despite the occurrence of minor experimental artifacts. The most toxic sediments were collected from Bear Creek; other areas exhibiting toxicity included the Inner Harbor and Colgate Creek. Marginal toxicity was observed in samples from Curtis Creek, Lazeretto Point, and Back River. Negative relationships were detected between survival and concentrations of select sediment-associated contaminants, whereas a very strong positive association existed between survival in laboratory exposures and density of L. plumulosus at the test sites. A weight of evidence approach, including correlation analyses, a model of polycyclic aromatic hydrocarbon bioavailability, and comparisons to benchmark sediment levels, was used to tentatively identify classes of contaminants that contributed to the observed toxicity. Analysis of results suggested that toxicity at stations in Bear Creek and Colgate Creek may have been driven by sediment-associated metals, whereas toxicity at stations in the Inner Harbor was likely due to both metal and organic contaminants. The observed relationships among toxicity test results, concentrations of sediment-associated contaminants, and abundance of L. plumulosus at the test sites suggests that acute toxicity tests with this species are indicative of adverse biological effects in the field.

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A 28-d partial life-cycle test with the estuarine amphipod Leptocheirus plumulosus was developed in response to the need for an assay to mimic chronic exposure to sediment-associated contaminants. To ensure that toxicity tests have environmental relevance, it is essential to evaluate the relationship between laboratory responses and field measures of contamination. Consequently, one objective of the study was to compare the results of the chronic sediment toxicity test with L. plumulosus to gradients of sediment contamination and the in situ benthic community in its native Chesapeake Bay. Chronic tests were conducted by two laboratories, the Army Corps of Engineers Waterways Experiment Station ([WES]; Vicksburg, MS, USA) and the University of Maryland ([UM] College Park, MD, USA) using different feeding regimes, providing the opportunity to evaluate the effect of this variable on response sensitivity. A second objective was to compare the relative sensitivity of acute and chronic tests with L. plumulosus with field-collected sediments. Overall, there was good agreement between the toxicological response of acute and chronic tests with L. plumulosus and field measures of contamination. Survival in the acute test and chronic test conducted by WES was negatively correlated with concentrations of sediment-associated contaminants. Survival in acute exposures was significantly reduced in sediments from 8 of 11 stations. Indigenous L. plumulosus were found only at two of the three stations that did not exhibit acute toxicity. An unexpected finding was the difference in responsiveness of the two chronic tests. Survival in tests conducted by UM and WES was significantly reduced in sediments from 4 and 6 of 11 stations, respectively. No additional sublethal toxicity was detected in the UM chronic test, but the WES test detected reproductive effects at two additional stations. We believe the observed differences were related to the test diet used. Partly as a result of our findings, the recommended diet for the L. plumulosus chronic test was changed in the final methods document.

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