Ecological Evaluation Technical Guidance - State of New Jersey

Toxicity Test DesignSediment toxicity studies are conducted by exposing a predetermined number oforganisms (e.g., eight replicates of ten organisms) to a sediment sample. Benthicorganisms are placed in beakers containing a layer of the sediment sample covered withclean laboratory water, and in test chambers containing clean laboratory sediment toserve as an experimental control. Investigators make direct observations of the exposedtest setup at regular intervals for the duration of the test to determine responses such aserratic behavior and visible mortality. However, sediment organisms quickly burythemselves in the test sediment and are not seen again until test termination when theyare removed for final enumeration.A second “reference” control should also be included in each study, using sediment fromoutside the influence of the site (e.g., upstream). Use of an appropriate reference areasediment is more representative of the actual background area stream conditions. While asite sediment may show a significant effect as compared to the laboratory control, it maynot show a significant effect when compared to the reference area.To perform statistical analyses to determine whether significant differences exist betweenthe site-related samples and laboratory controls or reference area samples, toxicity studiesshould be set up with multiple replicates. As a general rule, more replicates mean greaterstatistical power and more confidence in the final results. Acute sediment studies aretypically performed with eight replicates of ten organisms for each test sample, whichensures sufficient statistical power for the more sensitive sublethal growth endpoint.Toxicity Test EndpointsFor acute sediment toxicity studies, the endpoints include survival and growth. Survivalis assessed as a percentage of the number of organisms exposed at test initiation. Growthof amphipods, both freshwater and saltwater, is assessed as the dry weight of thesurviving organisms.Growth of midges is assessed as the ash-free dry weight (AFDW) of the survivingorganisms. Sediment grain size influences the amount of sediment that C. dilutus larvaeingest, and as a result, larvae exposed to finer-grained sediment will have more sedimentin their guts. Because most sediment sites have varying grain size distributions,significant bias can be added to the C. dilutus growth results. By measuring the dryweight of the surviving organisms at test termination, then ashing them to burn off anyorganic material, the weight of the sediment grains can be subtracted from the total dryweight to yield AFDW, which is the more appropriate endpoint.Data EvaluationAll statistical analyses are to be performed as specified in the USEPA and ASTMguidance documents. Data from site samples should be compared to the laboratorycontrols to determine whether observed toxic effects are statistically significant. Inaddition to the laboratory control, an appropriately selected field reference area sedimentmay yield results that are more representative of actual background area field conditions.If the upstream reference area sample shows toxic effects, it is possible that at least aportion of any toxic effect observed from the downstream sample is not related to the site.Ecological Evaluation Technical Guidance Document 112Version 1.2 8/29/12