Significance and Use
5.1 Sediment provides habitat for many aquatic organisms and is a major repository for many of the more persistent chemicals that are introduced into surface waters. In the aquatic environment, most anthropogenic chemicals and waste materials including toxic organic and inorganic chemicals can accumulate in sediment, which can in turn serve as a source of exposure for organisms living on or in sediment. Contaminated sediments may be directly toxic to aquatic life or can be a source of contaminants for bioaccumulation in the food chain.
5.2 The objective of a sediment test is to determine whether chemicals in sediment are harmful to or are bioaccumulated by benthic organisms. The tests can be used to measure interactive toxic effects of complex chemical mixtures in sediment. Furthermore, knowledge of specific pathways of interactions among sediments and test organisms is not necessary to conduct the tests. Sediment tests can be used to: (1) determine the relationship between toxic effects and bioavailability, (2) investigate interactions among chemicals, (3) compare the sensitivities of different organisms, (4) determine spatial and temporal distribution of contamination, (5) evaluate hazards of dredged material, (6) measure toxicity as part of product licensing or safety testing, (7) rank areas for clean up, and (8) estimate the effectiveness of remediation or management practices.
5.3 Results of toxicity tests on sediments spiked at different concentrations of chemicals can be used to establish cause and effect relationships between chemicals and biological responses. Results of toxicity tests with test materials spiked into sediments at different concentrations may be reported in terms of a LC50 (median lethal concentration), an EC50 (median effect concentration), an IC50 (inhibition concentration), or as a NOEC (no observed effect concentration) or LOEC (lowest observed effect concentration). However, spiked sediment may not be representative of chemicals associated with sediment in the field. Mixing time, aging and the chemical form of the material can affect responses of test organisms in spiked sediment tests (10.6).
5.4 Evaluating effect concentrations for chemicals in sediment requires knowledge of factors controlling their bioavailability. Similar concentrations of a chemical in units of mass of chemical per mass of sediment dry weight often exhibit a range in toxicity in different sediments (Di Toro et al. 1990 (4), 1991 (2)). Effect concentrations of chemicals in sediment have been correlated to interstitial water concentrations, and effect concentrations in interstitial water are often similar to effect concentrations in water-only exposures. The bioavailability of nonionic organic compounds and metals in sediment is often inversely correlated with the organic carbon concentration; moreover, the bioavailability of metals in sediment are often inversely correlated with acid volatile sulfide. Whatever the route of exposure, these correlations of effect concentrations to interstitial water concentrations indicate that predicted or measured concentrations in interstitial water can be used to quantify the exposure concentration to an organism. Therefore, information on partitioning of chemicals between solid and liquid phases of sediment is useful for establishing effect concentrations (DiToro et al. 1990 (4), 1991 (2); Wenning et al. 2005 (19)).
5.5 Field surveys can be designed to provide either a qualitative reconnaissance of the distribution of sediment contamination or a quantitative statistical comparison of contamination among sites. Surveys of sediment toxicity are usually part of more comprehensive analyses of biological, chemical, geological, and hydrographic data (USEPA 2002a, b, and c) (20-22). Statistical correlations may be improved and sampling costs may be reduced if subsamples are taken simultaneously for sediment tests, chemical analyses, and benthic community structure.
5.6 Table 1 lists several approaches used to assess of sediment quality. These approaches include: (1) equilibrium partitioning sediment guidelines (ESGs; USEPA 2003 (23), 2005 (24); Nowell et al. 2016 (25)), (2) empirical sediment quality guidelines (for example, probable effect concentrations, PECs; MacDonald et al. 2000 (26), Ingersoll et al. 2001 (27)), (3) tissue residues, (4) interstitial water toxicity, (5) whole-sediment toxicity with field-collected sediment tests and with sediment-spiking tests, (6) benthic community structure, and (7) sediment quality triad integrating data from sediment chemistry, sediment toxicity and benthic community structure (Burton 1991 (28), Chapman et al. 1997 (29), USEPA 2002a, b, and c (20-22)). The sediment assessment approaches listed in Table 1 can be classified as numeric (for example, ESGs), descriptive (for example, whole-sediment toxicity tests), or a combination of numeric and descriptive approaches (for example, PECs). Numeric methods can be used to derive chemical-specific effects-based sediment quality guidelines (SQGs). Although each approach can be used to make site-specific decisions, no one single approach can adequately address sediment quality. Overall, an integration of several methods using the weight of evidence is the most desirable approach for assessing the effects of contaminants associated with sediment (USEPA 2002a, b, and c (20-22), Wenning et al. 2005 (19), Guide E1525, Guide E3163). Hazard evaluations integrating data from laboratory exposures, chemical analyses, and benthic community assessments (the sediment quality triad) provide strong complementary evidence of the degree of pollution-induced degradation in aquatic communities (Burton 1991 (28), Chapman et al. 1997 (29)). Importantly, the weight of the evidence needed to make a decision (number of methods used) should be determined based on the weight (cost) of the decision.
Scope
1.1 Relevance of Sediment Contamination—Sediment provides habitat for many aquatic organisms and is a major repository for many of the more persistent chemicals that are introduced into surface waters. In the aquatic environment, both organic and inorganic chemicals may accumulate in sediment, which can in turn serve as a source of exposure for organisms living on or in sediment. Contaminated sediments may be directly toxic to aquatic life or can be a source of contaminants for bioaccumulation in the food chain.
1.2 Sediment Assessment Tools—Several types of information may be useful in assessing the risk, or potential risk, posed by sediment contaminants, including: (1) chemical analysis of sediment contaminants; (2) sediment toxicity tests, (3) bioaccumulation tests; and (4) surveys of benthic community structure. Each of these provides a different type of information to the assessment, and integrating information from all four lines of evidence may often provide the most robust assessments.
1.3 Strengths of Toxicity Testing of Contaminated Sediments—Directly assessing the toxicity of contaminated sediments provides some of the same advantages to sediment assessment that whole effluent toxicity testing provides to management of industrial and municipal effluents. As for effluent tests, direct testing of sediment toxicity allows the assessment of biological effects even if: (1) the identities of toxic chemicals present are not (or not completely) known; (2) the influence of site-specific characteristics of sediments on toxicity (bioavailability) is not understood; and (3) the interactive or aggregate effects of mixtures of chemicals present are not known or cannot be adequately predicted. In addition, testing the response of benthic or epibenthic organisms exposed via sediment provides an assessment that is based on the same routes of exposure that would exist in nature, rather than only through water column exposure.
1.4 Relating Sediment Exposure to Toxicity—One of the challenges with sediment assessment is that the toxicity of sediment contaminants can vary greatly with differences in sediment characteristics; a bulk sediment concentration (normalized to dry weight) may be sufficient to cause toxicity in one sediment, while the same concentration in another sediment does not cause toxicity (for example, Adams et al. 1985) (1).2 Factors such as the amount and characteristics of the organic carbon present in sediment can alter the bioavailability of many chemicals (Di Toro et al. 1991 (2); Ghosh 2007 (3)), as can other characteristics such as acid volatile sulfide or iron and manganese oxides (Di Toro et al. 1990 (4), Tessier et al. 1996 (5)). Direct measurement of toxicity in contaminated sediments can provide a means to measure the aggregate effects of such factors on the bioavailability of sediment toxicants.
1.5 Understanding the Causes of Sediment Toxicity—While direct testing of sediment toxicity has the advantage of being able to detect the effects of any toxic chemical present, it has the disadvantage of not providing any specific indication of what chemical or chemicals are causing the observed responses. Other techniques, such as spiked-sediment toxicity tests or Toxicity Identification Evaluation (TIE) methods for sediments have been developed and are available to help evaluate cause/effect relationships (USEPA 2007) (6).
1.6 Uses of Sediment Toxicity Tests—Toxicity tests conducted on sediments collected from field locations can be used to: (1) conduct surveys of sediment quality as measured by sediment toxicity; (2) prioritize areas of sediment for more detailed investigation of sediment contamination; (3) determine the spatial extent of sediment toxicity; (4) compare the sensitivity of different organisms to sediment contamination; (5) evaluate the relationship between the degree of sediment contamination and biological effects along a contamination gradient; (6) evaluate the suitability of sediments for removal and placement at other location (for example, dredged material disposal); (7) help establish goals for remedial actions; and (8) assess the effectiveness of remedial actions at reducing sediment toxicity. These applications are generally targeted at assessing the likely biological effects of bedded sediments at field sites at the time of sampling. However, toxicity testing of natural or artificial sediments spiked with known quantities of chemicals can also be used to evaluate additional questions such as: (1) determining the potency of a chemical to organisms exposed via sediment; (2) evaluating the effect of sediment composition on chemical bioavailability or toxicity; (3) informing chemical-specific risk assessments for chemicals that may accumulate and persist in sediments upon release; (4) establishing regulatory guidance for chemicals in water or sediment. Spiked sediment studies have the advantage of allowing uni-variate experiments in which exposure gradients can be reliably constructed; as such they lend themselves to the derivation of standardized point estimates of effect, such as a median lethal concentration (LC50) or concentration reducing sublethal performance by a specified amount, such as an effect concentration (for example, EC20 estimated to reduce weight of test organisms by 20 %).
1.7 Limitations—While some safety considerations are included in this standard, it is beyond the scope of this standard to encompass all safety requirements necessary to conduct sediment toxicity tests.
1.8 This standard is arranged as follows:
|
| Section |
| Scope | 1 |
| Referenced Documents | 2 |
| Terminology | 3 |
| Summary of Test Methods | 4 |
| Significance and Use | 5 |
| Interferences | 6 |
| Water, Formulated Sediments, Reagents | 7 |
| Health, Safety, Waste Management, Biosecurity | 8 |
| Facilities, Equipment, and Supplies | 9 |
| Sample Collection, Storage, Characterization, and Spiking | 10 |
| Quality Assurance and Quality Control | 11 |
| Collection, Culturing, and Maintaining the Amphipod Hyalella azteca and the Midge Chironomus dilutus | 12 |
| Interpretation of Results and and Reporting | 13 |
| Precision and Bias | 14 |
| Keywords | 15 |
| Annexes |
|
| Guidance for 10-d Sediment or Water Toxicity Tests with the Amphipod Hyalella azteca | Annex A1 |
| Guidance for 42-d Sediment or Water Reproductive Toxicity Tests with the Amphipod Hyalella azteca | Annex A2 |
| Guidance for 10-d Sediment or Water Toxicity Tests with the Midge Chironomus dilutus | Annex A3 |
| Guidance for Sediment or Water Life Cycle Toxicity Tests with the Midge Chironomus dilutus | Annex A4 |
| Guidance for Sediment Toxicity Tests with Juvenile Freshwater Mussels | Annex A5 |
| Guidance for Sediment Toxicity Tests with the Midge Chironomus riparius | Annex A6 |
| Guidance for Sediment Toxicity Tests with Mayflies (Hexagenia spp). | Annex A7 |
| Guidance for Sediment Toxicity Tests with the Oligochaete Tubifex tubifex | Annex A8 |
| References |
|
1.9 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific hazard statements are given in Section 8.
1.10 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
