EVALUATION OF POTENTIAL CONFOUNDING FACTORS IN SEDIMENT TOXICITY TESTS WITH THREE FRESHWATER BENTHIC INVERTEBRATES

We examined the effects of natural sediment physicochemical properties on the results of lab tests with the amphipod Hyalella azteca, the midge Chironomus tentans, and the ohgochaete Lumbriculus variegatus Ten-day exposures with the three species were conducted with 50 uncontaminated sediment samples from Lakes Erie, Huron, Superior, and Ontario, which differed markedly with regard to characteristics such as grain-size distribution, organic carbon content, and mineralogical composition Tests were conducted both with and without the addition of exogenous food Survival of Hyalella azteca, survival and growth of Chironomus tentans, and survival/reproduction and growth of Lumbriculus vanegatus were significantly greater in tests in which the animals were fed vs those in which they were not Approximately 10% of the tests in which Hyalella azteca was not fed and 80% of tests in which the amphipods were fed resulted in >80% survival, a common criterion for defining the acceptability of tests with Hyalella azteca in clean control sediments Similarly, a relatively high percentage of the tests in which Chironomus tentans was not fed would have failed a control survival criterion of 70% for the midge Hence, there is significant potential for false positive results if Hyalella azteca or Chironomus tentans is not fed during sediment tests Predictive modeling of the assay results in relationship to sediment physicochemical characteristics failed to reveal any additional factors that influenced survival of Hyalella azteca and Chironomus tentans, or reproduction and growth of Lumbriculus vanegatus in tests in which the organisms were fed However, linear modeling did suggest that growth of fed as well as unfed Chironomus tentans may have been influenced by gram size distribution of the test sediments