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EFFECTS ASSESSMENT
representative organisms and the selection of standardised sediments are still being discussed.
Various approaches (e.g. equilibrium partitioning, interstitial water quality, spiked sediment
toxicity, tissue residue, derived sediment quality criteria and standards) are being developed to
investigate the effects that chemicals have on sediment and sediment organisms (OECD, 1992b).
Only whole-sediment tests using benthic organisms are suitable for a realistic risk assessment of
the sediment compartment. It is only by using such tests that it is possible to adequately address
all routes of exposure. A PNECsed can be derived from these tests that can be compared with the
predicted concentration in the sediment (PECsed) (based on measured or estimated values). Test
procedures are described in ASTM (1990 a–e), ASTM (1991, 1993 & 1994) and Burton (1991 &
1992). No finalised international guidelines for whole-sediment tests are available. However, a
draft OECD guideline for a chironomid toxicity test using spiked sediment exists (OECD,
2001e). In addition OECD has prepared a detailed review paper on aquatic ecotoxicity tests
including sediment test methods (OECD, 1998a). Examples of sediment toxicity tests for which
protocols are available are listed in Appendix VI.
Statistical extrapolation methods for calculation of PNEC for sediment organisms could be used
when sufficient data are available (cf. Section 3.3.1.2.). Further guidance needs to be developed
in future.
3.5.2 Strategy for effects assessment for sediment organisms
Substances that are potentially capable of depositing on or sorbing to sediments to a significant
extent have to be assessed for toxicity to sediment-dwelling organisms. In addition, marine
sediment effects assessment is necessary for substances that are known to be persistent in marine
waters, and may accumulate in sediments over time. In general, substances with a Koc < 500 –
1000 L/kg are not likely sorbed to sediment (SETAC, 1993). To avoid extensive testing of
chemicals a log Koc or log Kow of ≥ 3 can be used as a trigger value for sediment effects
assessment.
For most chemicals the number of toxicity data on sediment organisms will be limited. For the
initial risk assessment, normally no effect data from tests with sediment organisms will be
available. Therefore, the equilibrium partitioning method is proposed as a screening approach to
compensate for this lack of toxicity data. Results from this screening can be used as a trigger for
determining whether whole-sediment tests with benthic organisms should be conducted. Tests
with benthic organisms using spiked sediment are likely to be necessary if, using the equilibrium
partitioning method, a PEC/PNEC ratio > 1 is derived. The test results will enable a more
realistic risk assessment of the sediment compartment to be carried out.
Three situations can be distinguished for deriving a PNECsed:
• when no toxicity test results are available for sediment organisms, the equilibrium
partitioning method is applied to identify a potential risk to sediment organisms. This
method is regarded as “screening approach” and is explained in Section 3.5.3;
• when only acute toxicity test results for benthic organisms are available (at least one) the
risk assessment is performed both on the basis of the test result of the most sensitive species
using an assessment factor of 1000 and on the basis of the equilibrium partitioning method.
The lowest PNECsed is then used for the risk characterisation;
• when long-term toxicity test data are available for benthic organisms the PNECsed is
calculated using assessment factors for long-term tests and this result should prevail in the
risk assessment. This approach is explained in Section 3.5.4.
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