When considering nickel toxicity in sediments, it is important to account for sediment bioavailability. Bioavailability models based on AVS binding have subsequently been developed to normalize nickel ecotoxicity data to a common site condition when deriving HC5/PNECs or sediment standards. This fact sheet presents the background information on the available sediment nickel bioavailability models and demonstrates how this information can be used to estimate site-specific bioavailable PNEC values. The availability of sediment physico-chemistry data, such as AVS content can be limited in some cases but sampling analyzing AVS concentrations can be done in a reproducible way allowing site-specific PNEC values to be calculated and a more accurate site-specific risk characterization to be conducted. However, the sole use of the SEM-AVS concept for nickel is conservative as it has been demonstrated that even in the absence of AVS, as is the case in oxic sediments, other partitioning phases such as binding to iron and manganese oxides may mitigate nickel toxicity in sediments (Costello et al., 2011).