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Sediment toxicity

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Key value for chemical safety assessment

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A total risk approach using SSD was performed by the European copper institute, ECI (2008)

"The sediment PNEC included using a weight of evidence approach considering different sources and tiered approaches of information: (1) sediment ecotoxicity data, (2) pelagic ecotoxicity data in combination with Kd values derived through different approaches, (3) soil ecotoxicity data and soil bioavailability models and (4) mesocosm/field ecotoxicity.

 

High-quality chronic benthic NOECs for six benthic species, representing 62 NOEC values were retained for the PNEC derivation. NOEC values were related to sediment characteristics (e.g., Organic Carbon (OC) and Acid Volatile Sulphides (AVS)), influencing the bioavailability and thus toxicity of copper to benthic organisms. The derivation of the freshwater HC5-50sediment for copper was therefore based on the OC-normalized dataset, containing only low-AVS sediments. Using the log-normal species sensitivity distribution a freshwater HC5-50sediment of 1741 mg Cu/kg OC was derived through the statistical extrapolation method.

 

Using the equilibrium partitioning (EqP) approach, the derived HC5-50sediment (EP) values were comparable or higher than the HC5-50 derived from whole sediment tests. The comparison between the sensitivity of soil and benthic organisms added weight to the HC5-50 from whole sediment tests. The same did sediment threshold values and benthic NOECs that were obtained from four mesocosm studies and one field cohort study.

 

The HC5-50 (AF=1) of 1741 mg Cu/kg OC, corresponding to 87 mg Cu/kg dry weight for a sediment with 5 % O.C.(TGD default value) was carried forward as reasonable worst case PNEC for Europe in a generic context. The AF of 1 has been chosen in relation to the uncertainty considerations covering 1) weight of evidence provided; 2) the overall quality of the database; 3) the robustness of the HC5-50 values; 4) corrections for bioavailability (reducing uncertainty); 5) the conservative factor built into the system (no acclimation of the test organisms and only low AVS sediments retained); 6) validations from multi-species mesocosm studies and field studies and 7) comparison with natural backgrounds and optimal concentration ranges.

 

In case of natural sediments both the amount of AVS and organic carbon present in the sediment has dictated the observed effect levels for copper and were used for the risk characterisation. In absence of AVS data, a default AVS value of 0.77 μmol/kg dry weight was used. This value corresponded to the 10th percentile of the AVS obtained from a wide Flemish monitoring database and additional AVS data from other European countries. "

Reference: European Copper Institute, ECI (2008). Voluntary Risk Assessment Report on Copper and its compounds.