Ecological Evaluation Technical Guidance - State of New Jersey

the advantage of exposing organisms in a more stream-like manner, but they aresignificantly more labor intensive and are also more expensive than the other twotest types.Toxicity Test Duration - Acute or ChronicSediment toxicity is generally assessed in the laboratory using acute or chronic studies.Acute sediment studies take ten days (though screening assays may be shorter), and aredesigned to determine whether the sediment sample in question will kill the exposedorganisms or impact their growth. Chronic studies are longer, usually 20 days or more(some exceeding 50 days), and are designed to determine sublethal effects on growth,emergence and reproduction. While observed lethality is a direct indication that thesample in question is toxic, sublethal effects can be important for the assessment of longtermpopulation health. In ecological risk assessments, chronic toxicity tests aregenerally considered to be the preferred alternative. The NJDEP and USEPA Region 2BTAG have routinely recommended the use of ASTM E1706 - 05(2010) Standard TestMethod for Measuring the Toxicity of Sediment-Associated Contaminants withFreshwater Invertebrates. The previous version of this standard (Test Method E1706-95b) described 10-day toxicity tests with the amphipod Hyalella azteca and midgeChironomus. This version of the standard now outlines approaches for evaluatingsublethal endpoints in longer-term sediment exposures with these two species (Annex A6and Annex A7).However, in highly urbanized settings where there are numerous sources effecting a site,the longer-term sublethal studies are not always appropriate for environmental sedimentsamples because the short term toxicity tests are adequate to measure potential impactsassociated with the site. Sensitive sublethal tests are good for testing chemicals andwastewater solutions that can be diluted to different concentrations (e.g., 100%, 50%,25%, 12.5% and 6.25%) at which a dose response becomes apparent. If a responseunrelated to dose is observed (e.g., effect at 25%, but not at 100%), the test is suspect.When testing sediment samples, they are not diluted and are tested as 100 percent versusa laboratory control or reference area sample. If there is a sublethal effect, investigatorsmay not be able to tell whether it is related to the sample or to the inherent variability ofthe biological system being tested.Variability is expected even in the laboratory's Standard Reference Toxicant (SRT)studies. Labs perform regular SRT tests to assess the health of each batch of testorganisms and the procedures used by the technicians setting up the tests. The SRTstudies are typically short-term (96 hours or shorter), water-only tests that use a commonreagent-grade salt (e.g., KCl). The USEPA (2000a) states that even though the final SRTresult is allowed to fall within two standard deviations of the laboratory's historical mean,the laboratory is expected to have up to 10 percent of SRT tests fall outside of that range.It is not until the lab has more than 10 percent SRT failures that a problem is noted.Because USEPA expects so much variability in a short-term test with lab water andreagent salts, it is within reason to expect that long-term, sublethal effects from complexmixtures like site sediment will yield substantially more variability.Ecological Evaluation Technical Guidance Document 111Version 1.2 8/29/12