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MARINE RISK ASSESSMENT
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 existing chemicals the number of toxicity data on infaunal and epibenthic organisms
will be limited. As a screening approach the equilibrium method can be used to compensate for
the lack of toxicity data if a PECmarine sediment can be determined on the basis of a measured
concentration of the substance in water that is independent of the value of the Koc. If the
PEC/PNEC determined using this method is > 1 then the need for testing with benthic organisms
using spiked sediment should be considered.
It is not necessary to apply the equilibrium partitioning method to predicted environmental
concentrations obtained from application of an exposure model when such a model will have
used the same Koc or log Kow value as that used to predict the PNECsediment. The reason is that
the resulting PEC/PNEC ratio for sediment will have the same value as for the water
compartment. In this case no quantitative risk characterisation for marine sediment should be
performed. Under these circumstances the assessment conducted for the aquatic compartment
will also cover the sediment compartment for chemicals with a log Kow up to 5. For substances
with a log Kow > 5 (or with a corresponding Koc), however, the PEC/PNEC ratio for the aquatic
compartment is increased by a factor of 10. The increased factor is justified by the fact that the
equilibrium partitioning method considers mainly the exposure via the water phase and does not
include that potential additional accumulation via sediment ingestion may occur for certain types
of sediment dwelling invertebrates (see Section 8.2.3).
Four situations can be distinguished for deriving a PNECsediment:
1. where only results from acute tests with benthic freshwater organisms are available (at least
one) the risk assessment is performed both on basis of the tests and on the basis of the
equilibrium partitioning method. The lowest PNECmarine sediment is then used for the risk
characterisation.
2. where, in addition to the tests with freshwater benthic organisms, an acute toxicity test is
performed with a marine benthic organism that is preferably representative of the same
taxon that is judged to be the most sensitive in the freshwater tests. Under these
circumstances an assessment factor of 1000 is applicable. A reduction of the assessment
factor is only justified if sufficient long-term tests with sediment-dwelling organisms are
available, and, if possible, where other evidence indicates that these tests include sensitive
taxonomic groups. Also in this case a comparison with the screening approach has to be
made and the lowest PNECsediment should be used for the risk characterisation.
3. where long-term toxicity data are available for benthic freshwater organisms. Under this
circumstance the PNECmarine sediment is calculated using assessment factors for long-term tests.
This approach is explained in Section 4.3.2.4.
4. where long-term toxicity data are available for benthic freshwater and a minimum of two
marine organisms. Under these circumstances a PNECmarine sediment is calculated using the
lower assessment factors that are associated with data obtained from long-term tests. A
PNECmarine sediment obtained from such data is preferred for risk assessment. This approach is
explained in Section 4.3.2.4.
Table 18 in Section 3.5.2 presents an overview of different data configurations and explains how
to use them for the risk characterisation for sediment. Attention should be paid to the fact that
very often contaminants are not analysed in whole sediment but in a certain fraction of the
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