Nickel Bioavailability Models

Bioavailability and chronic toxicity of nickel to sediment organisms varies based on sediment characteristics. To make comparisons between laboratory toxicity data, results must be normalized to a common set of conditions using bioavailability models. Bioavailability models can be used to derive site-specific HC5/PNEC values for sites in which appropriate sediment properties have been quantified. For nickel, chronic sediment toxicity tests are available for 10 species of sediment dwelling organisms conducted in nickel-spiked sediments representing sediments with low and high nickel binding capacity (i.e. low AVS/Low TOC and high AVS/high TOC) (See Fact Sheet 8). In addition, chronic toxicity tests were conducted with several additional nickel-spiked sediments with a wide range of AVS and TOC concentrations to characterize relationships for 7 test species between nickel toxicity and sediment characteristics (i.e. bioavailability regression models) (Besser et al., 2013; Vangheluwe and Nguyen, 2015; Vangheluwe et al., 2013). The chronic regression models for nickel were developed/calibrated based on sediments that represent the full range in physico-chemical parameters (AVS, OC) representative for the EU. EC20 values, expressed as either total recoverable nickel or SEMnickel, showed significant relationships with a range of sediment parameters, including AVS, total recoverable iron, TOC, CEC, silt, total recoverable manganese, and SEMmanganese. The importance of sediment phases other than AVS indicates that the relationships should be relevant for oxic sediments as well as anoxic sediments. For all species tested, the sediment parameter showing the strongest linear relationship was AVS. AVS has already been demonstrated as being one of the predominant factors controlling toxicity of divalent metals (Di Toro et al., 1992; Ankley et al., 1991 and 1996). An overview of the slopes and intercepts of all significant regression models relating the toxicity of nickel ([Ni] in mg/kgdw) to AVS in sediments is presented in Table 1.

Although the effect of decreasing toxicity with increasing AVS was consistently observed for all species, the magnitude of the effect was not similar among species, and these differences appear to be linked with organism behavior. The strongest mitigating effects of AVS are observed for those species with an epibenthic lifestyle such as H. azteca, S. corneum, and G. pseudolimnaeus, with slopes ranging from 0.358 to 0.492 (Table 1). The relationships are less pronounced for the benthic species T. tubifex, C. riparius, Hexagenia sp., and E. virgo that exhibit more burrowing activity and subsurface feeding (i.e. slopes ranging from 0.125-0.22).