Environmental risks are typically characterized in the risk assessment framework by comparing exposure concentrations and critical effect concentrations. In Organisation for Economic Co-operation and Development (OECD) countries, critical effect concentrations for metals are based on Predicted No Effect Concentrations (PNEC), which are typically derived from long-term laboratory-spiked ecotoxicity tests performed with highly soluble, almost completely dissociated metal salts in artificial laboratory standard sediments or natural sediments. It has been recognized that results from these whole sediment tests may be influenced by several parameters (e.g., sediment composition, spiking method, feeding mode, bioavailability) and that caution is needed in selecting and developing the appropriate test methods. For example, traditional sediment spiking methods that involve adding soluble nickel metal salts to sediments without further pH amendment result in significant diffusion of nickel from the sediment compartment to the water compartment (Vandegehuchte et al., 2007). During 2011-2015, a multi-laboratory, multiphase research project was conducted to address this issue (i.e. unrealistic high exposure conditions) and to provide a scientific basis to derive a bioavailability based approach for assessing risks of nickel (Ni) in sediments (Schlekat et al., 2016). Besides developing new spiking procedures (Brumbaugh et al., 2013), the nickel sediment research program demonstrated that the chronic toxicity of nickel in sediments was influenced by several physicochemical characteristics of the tested sediments, with the highest toxicity found in sediments with low Acid Volatile Sulfides (AVS) concentrations, low Total Organic Carbon (TOC), low total recoverable iron (Fe), and low Cation Exchange Capacity (CEC) (Besser et al., 2013; Vangheluwe et al., 2013; Vangheluwe and Nguyen, 2015). Therefore, nickel toxicity can vary considerably among sediments with different physico-chemical characteristics and tests with the same sediment species that are performed using different sediment types can produce different results. Consequently, bioavailability models were developed to directly compare sediment toxicity and to generate sediment threshold values, e.g., PNECsed.

This fact sheet provides an overview of the nickel sediment bioavailability models and demonstrates how this information can be used to estimate site-specific bioavailable nickel PNEC values. The availability of sediment physico-chemistry data, such as AVS content, allows site-specific nickel PNEC values to be calculated and a more accurate site-specific risk characterization to be conducted.