Ecological Evaluation Technical Guidance - State of New Jersey

If no historical aquatic toxicity information is available, investigators can perform 24-hour to 96-hour acute toxicity studies to determine whether the samples are acutely toxic.If no acute toxicity is observed, investigators can initiate short-term chronic toxicitystudies. Acute toxicity studies are quicker and cheaper than chronic studies. However,because aqueous samples can be diluted, it is often easier to go straight to the short-termchronic toxicity test, including a series of dilutions (sample mixed with clean laboratorywater). For ERAs, chronic studies are often more appropriate because of the long-termexposure of the receptors to the contaminant of potential ecological concern (COPECs)(assessment of maintenance and reproduction of a healthy population).Toxicity Test DesignAquatic toxicity studies are conducted by exposing a predetermined number of organisms(e.g., four replicates of ten organisms) to an undiluted sample or to a series ofconcentrations of a surface water or wastewater sample. Aquatic organisms are placed inappropriate test chambers (e.g., beakers, flasks, test tubes) containing the samples, and intest chambers containing clean laboratory water to serve as an experimental control.Investigators make direct observations of the exposed test organisms at regular intervalsfor the duration of the test to determine responses such as mortality, reduction in growth,or reduced reproduction.Surface water and wastewater samples can be tested undiluted at 100 percent strength;however, if toxicity is observed, such a test does not indicate how toxic the sample is.Both USEPA and NJDEP recommend using five serial dilutions of the sample water(e.g., 100%, 50%, 25%, 12.5% and 6.25%) mixed with clean laboratory water. The cleanlaboratory water is also used as a negative control to assess the health of the testorganisms (if toxic effects are noted in laboratory water, the batch of test organisms isconsidered suspect, and the test may have to be re-run using a different batch oforganisms). A second “reference” control can also be included in the study, using surfacewater from outside the influence of the site (e.g., upstream).To perform statistical analyses to determine whether significant differences exist betweenthe laboratory controls or reference area samples, toxicity studies should be set up withmultiple replicates. As a general rule, more replicates mean greater statistical power andmore confidence in the final results. Acute toxicity studies are typically performed withtwo replicates of ten organisms for each test concentration, which is sufficient forcalculation of lethal concentrations.Short-term chronic toxicity studies should be performed with four or more replicates often organisms per exposure concentration for fish and mysid shrimp, and with tenreplicates of a single organism per exposure concentration for Ceriodaphnia. Replicationensures sufficient statistical power for the more sensitive sublethal endpoints (e.g.,growth and reproduction).Toxicity Test EndpointsFor acute toxicity studies, the typical endpoint is lethality, which is generally expressedas the LC 50 (the concentration of test water that kills half of the exposed organisms).Statistical calculation methods are discussed at length in the USEPA guidance manual.Ecological Evaluation Technical Guidance Document 107Version 1.2 8/29/12