Dialuminium nickel tetraoxide

Sediment toxicity

Additional information

PNEC sediment: Pending outcome of sediment testing program

A technical conclusion ii (no further information or testing required) was determined for all compartments of the EU Ni Risk Assessment except for the sediment compartment, which received a technical conclusion i (further information or testing required). EU Member States and the ECB (European Chemicals Bureau) have accepted a formal testing recommendation for sediments, which was published in the Official Journal of the European Union on May 28th, 2008.

The need for additional testing was the conclusion that the ecotoxicity results of the whole sediment toxicity tests conducted under the historic conclusion i) research program (2004-2005) were confounded by technical issues associated with the introduction of Ni into sediments in the laboratory, and the subsequent diffusional loss of Ni into overlying water. Briefly, relatively poor sorption of Ni to sediment particles resulted in the loss of dissolved Ni from the sediments. Furthermore, observed toxicity to the sediment toxicity test organisms was explained by Ni concentrations in overlying water, as opposed to Ni concentrations in the sediments. Interpretation of these ecotoxicity data required that conservative assumptions be applied to the outcome of these tests, which resulted in PNECsed (Predicted No Effects Concentration for nickel in sediments) values that were below ambient and natural background concentrations. These PNECsed values were neither scientifically defensible nor sustainable and their application would have led to the conclusion of risk at 100% of the operational sites within the RA, as well as at the regional scale. As such, the Danish Rapporteur and otherrecommended that further testing be conducted to generate the data to calculate a scientifically sound PNECsed, based on laboratory approaches aimed at controlling the diffusional loss of Ni from sediments and that could be validated in the field. The generation of these data will eliminate much of the uncertainty in the PNECsed derivation and bring closure to the conclusion i) for sediment.

 

To derive PNECsed values, the proposed research will be comprised of three components, including:

1. an evaluation of optimal sediment spiking techniques,

2. generation of reliable ecotoxicity data on sediment dwelling organisms providing effect concentrations relating to bulk sediment concentrations;

3. the development of an integrated, equilibrium-partitioning based bioavailability model for normalizing the sediment effect concentrations to bioavailable sediment concentrations under both aerobic and anaerobic conditions

 

Research proposals received by NiPERA have been designed to specifically address these components. Research proposed by the U.S. Geological Survey (USGS) would evaluate multiple spiking methods to determine the distribution of Ni between pore-water and solid-sediment phases over time and would be compared to the distribution of Ni in naturally Ni contaminated field collected sediments under laboratory conditions. (The partitioning of Ni in spiked sediments would also be compared to Ni partitioning in the field, which would be used to validate the optimal spiking strategy to be used for further ecotoxicity testing. This research would be conducted by Natural Resources Canada/University ofand would be sponsored jointly by Rio Tinto). Once the optimal spiking approach is identified, extensive ecotoxicity testing would be conducted for nine benthic organisms and for eight sediment types to evaluate the bioavailability of Ni in a wide range of sediments and toxicity to a variety of benthic organisms, to provide effect concentrations relating to bulk sediment concentrations. These data would then be used to generate an integrated bioavailability model for toxicity in sediments. The toxicity model would be field-validated using an approach proposed byof.

A Technical Conclusion i) group was formed to provide technical guidance on the development of a scientifically defensible approach for the Ni sediment toxicity test program. The Technical Conclusion i) group is composed of sediment experts from academia, consulting, and EU Member States.