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(IP08) The ten-day amphipod toxicity test: Laboratory vs. Field Responses.
Anghera, Michelle*,1, Ambrose, Richard1,2, Bay, Steve3, 1 University of California, Los Angeles, Department of Environmental Health Sciences, Los Angeles2 Envrionmental Sciences and Engineering Program, Los Angeles, CA3 Southern California Coastal Water Research Project, Westminster, CA, USA
ABSTRACT- Assessing sediment quality and impacts on benthic infauna populations has been challenging for scientists, especially in moderately contaminated wetlands. The ten-day amphipod toxicity test, a standard EPA method for determining sediment toxicity, is conducted by exposing amphipods to sediments in a laboratory under controlled conditions. Laboratory sediment toxicity tests often disturb redox gradients in the sediment do not incorporate daily variations in habitat characteristics (e.g., temperature), factors that may influence the response of the test organisms. Incorporating the more ecologically relevant in situ toxicity test in addition to the laboratory test may increase our understanding and interpretation of toxicity test responses. To determine the similarity of in situ and laboratory 10-day toxicity tests, both types of tests were run simultaneously using the amphipod Eohaustorius estuarius in February 2002. A field chamber was designed for an in situ ten-day amphipod test. The field test exposed the organisms to tidal cycles and daily variations in temperature and salinity. The laboratory test exposed organisms in a 1L glass jar containing 200 mL of sediment and 800 mL of overlying water at 15oC and salinity of 20 ppt. Field and lab responses were significantly different at 3 out of 5 sites. The field tests were significantly more sensitive than the laboratory. Variability (coefficient of variation) associated with survivorship was greater in the field (63-223%) than in the laboratory (12-85%). In the field; higher amphipod survivorship was associated with the presence of bivalves. This is most likely due to increased oxygen levels in the sediment due to bioirrigation by the bivalves.
Key words: wetlands, amphipod toxicity tests, sediment toxicity tests, in situ bioassays
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