Nickel dihydroxide

Sediment toxicity

Additional information

In OECD SIAP (2008) and EU-Risk Assessment (2008) the hazard of Nickel has been investigated extensively.

The classical Equilibrium Partitioning - Kp approach to derive the PNEC sediment failed to deliver reliable values. A comprehensive sediment testing program was therefore initiated in support of the EU Risk Assessment of Nickel, and included testing for six species of benthic invertebrates in a range of sediment types.

 

The chronic data generated by this program in combination with additional data collected from open literature formed the basis for the PNEC sediment derivation using a Species Sensitivity Distribution (SSD). However, the results of the laboratory experiments were confounded by the diffusion of nickel from the spiked sediments into the overlying water. In fact, it was shown that the concentration of nickel in the overlying water in thesemi-static test system generally correlated better with the observed effect concentrations on the sediment organisms than the nickel concentrations measured in the bulk sediment. Therefore, extensive calculations were necessary to extrapolate from overlying water nickel concentrations to sediment concentrations using the equilibrium partitioning approach. The very cautious assumptions that were necessarily taken in this extrapolation implied a high degree of scientific uncertainty. As a consequence, a high assessment factor was deemed appropriate when calculating the PNEC from the estimated HC5(50%) (55 mg Ni/kg based on 5% sediment organic carbon) based on the above mentioned approach. The scientific uncertainty of the described approach yielded a PNECsed of 18.3 mg Ni/kg, which is close to or below nickel background concentrations in many sediments of EU countries.

 

Based on the results of the draft Sediment Effects Assessment and the impact of this PNECsed on risk characterization for the sediment compartment it was determined that all local sites would be estimated to be at risk, and that risk would be concluded at the regional scale as well. Because of this and because the PNECsed was also shown to be below a generic natural background concentration of 29 mg Ni/kg for EU countries, it was concluded that the current sediment data set should not be used to derive a PNEC sediment and that additional research was warranted for generation of scientifically justified nickel sediment toxicity test data in order to derive a reliable PNEC for the sediment compartment.

 

To this end, a subsequent sediment testing program has been initiated, with the goal of performing tests in a way that limits the release of dissolved Ni from sediments to the overlying water similar to those of relevant natural systems. The results of this research will be reported post-SIAM as soon as it has been completed and the results analysed.