ASTM E2591-07(2013)

5.1 While federal criteria and state standards exist that define acute and chronic “safe” levels in the water column, effects levels in the sediment are poorly defined and may be dependent upon numerous modifying factors. Even where USEPA recommended Water Quality Criteria (WQC, (35)) are not exceeded by water-borne concentrations, organisms that live in or near the sediment may still be adversely affected (36). Therefore, simply measuring the concentration of a chemical in the sediment or in the water is often insufficient to evaluate its actual environmental toxicity. Concentrations of contaminants in sediment may be much higher than concentrations in overlying water; this is especially true of hydrophobic organic compounds as well as inorganic ions that have a strong affinity for organic ligands and negatively-charged surfaces. Higher chemical concentrations in sediment do not, however, always translate to greater toxicity or bioaccumulation 5.2 Amphibians are often a major ecosystem component of wetlands around the world, however limited data are available regarding the effects of sediment-bound contaminants to amphibians 5.3 Results from sediment testing with this procedure may be useful in developing chemical-specific sediment screening values for amphibians.

5.4 Sediment toxicity test can be used to demonstrate the reaction of test organisms to the specific combination of physical and chemical characteristics in an environmental medium. The bioavailability of chemicals is dependent on a number of factors, which are both site-specific and medium-specific. Although many of these factors can be estimated using equilibrium partitioning techniques, it is difficult to account for all the physical and chemical properties which could potentially affect bioavailability. Sediment toxicity tests may be particularly applicable to evaluating hydrophobic compounds which may not readily partition into the water column. See Table 1 for a summary of advantages and disadvantages associated with sediment toxicity tests.

1.1 This standard covers procedures for obtaining laboratory data concerning the toxicity of test material (for example, sediment or hydric soil (that is, a soil that is saturated, flooded, or ponded long enough during the growing season to develop anaerobic (oxygen-lacking) conditions that favor the growth and regeneration of hydrophytic vegetation)) to amphibians. This test procedure uses larvae of the northern leopard frog (Rana pipiens). Other anuran species (for example, the green frog (Rana clamitans), the wood frog (1.2 The test procedure describes a 10-d whole sediment toxicity test with an assessment of mortality and selected sublethal endpoints (that is, body width, body length). The toxicity tests are conducted in 300 to 500-mL chambers containing 100 mL of sediment and 175 mL of overlying water. Overlying water is renewed daily and larval amphibians are fed during the toxicity test once they reach Gosner stage 25 (operculum closure over gills). The test procedure is designed to assess freshwater sediments, however, R. pipiens can tolerate mildly saline water (not exceeding about 2500 mg Cl^-/L, equivalent to a salinity of about 4.1 when Na⁺ is the cation) in 10-d tests, although such tests should always include a concurrent freshwater control. Alternative test durations and sublethal endpoints may be considered based on site-specific needs. Statistical evaluations are conducted to determine whether test materials are significantly more toxic than the laboratory control sediment or a field-collected reference sample(s).

1.3 Where appropriate, this standard has been designed to be consistent with previously developed methods for assessing sediment toxicity to invertebrates (for example, Hyalella azteca and 1.4 Many historical amphibian studies, both water and sediment exposure, have used tests of shorter duration (5 days or less) (for example, 4-7) and, although both survival and sublethal endpoints were often assessed, there is substantive evidence that tests of longer duration are likely to be more sensitive to some contaminants 1.5 The methodology presented in this standard was developed under a Department of Defense (DoD) research program and presented in a guidance manual for risk assessment staff and state/federal regulators involved in the review and approval of risk assessment work plans and reports 1.6 The use of larval amphibians to assess environmental toxicity is not novel. Researchers have used tadpoles to examine toxicity of metals and organic compounds. Most of these studies have been through water exposure, usually in a manner similar to fish or invertebrate exposure as described in Guide E729 1.6.1 Sediment toxicity tests conducted in the laboratory with amphibians were performed over a range of test durations from 4 d (4, 31, Guide E1439-98 Appendix X2) to 12 d 1.6.2 To assess the effect of direct contact with the sediments containing PCBs, Savage et al. 1.6.3 Sediment toxicity testing with 1.7 Sediment toxicity tests are an effective means for evaluating the impact of sediment contamination on amphibians in a multiple lines of evidence paradigm. The evaluation is most powerful when toxicity testing sampling stations are co-located with sediment analytical chemistry samples and ecological surveys, allowing for a detailed evaluation of the co-occurring data in the ecological risk assessment. The spatial and temporal co-location of toxicity testing and analytical samples is particularly important for establishing contaminant-specific effects and assessing contaminant bioavailability.

1.8 In order for a sediment toxicity test to be sensitive it must be of sufficient duration to measure potential toxicity and it must be conducted during the appropriate developmental stage of the test organism’s life cycle. Using recently hatched tadpoles and conducting the sediment exposure test for 10 d to allow the evaluation of growth endpoints meets both of these sensitivity requirements.

1.9 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.10 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.