Nickel difluoride

Endpoint summary

Description of key information

Environmental fate data available for the nickel ion (Ni2+) is summarized in the following table:

 

Hydrolysis	Waived as abiotic degradation is irrelevant for inorganic substances assessed on an elemental basis.
Biodegradation	Waived based on the inorganic nature of the substance.
Bioaccumulation	The endpoint is covered by a category read-across approach. Aquatic bioaccumulation: BCF = 270 l Ni/kg  Terrestrial bioaccumulation: BAF = 0.3
Adsorption/desorption	The endpoint is covered by a category read-across approach. Soil: log Kp = 2.86 l Ni/kg Suspended matter: log Kp = 4.42 l Ni/kg Sediment: log Kp = 3.85 l Ni/kg Sewage sludge: log Kp = 3.2 l Ni/kg

Additional information

The bioaccumulation and adsorption/desorption endpoints were covered by read-across to nickel-based compounds. A categorical approach was selected for read-across, where quantitative variations in effects are predicted based on quantitative variations in bioavailability of Ni ion among category members. Environmental effects of all compounds in the category are caused by transformation of the nickel compounds to produce dissolved nickel ions (Ni2+). Details on the read-across approach can be found in the attached read-across justification (see attachement).

 

Link between Transformation/dissolution data and read-across approach justification

Under environmentally relevant conditions, nickel salts readily dissociate upon dissolution in aqueous media. Dissociation is a reversible process and the proportion of dissociated salt present is dependent on the pH and composition of the solution and the metal-ligand dissociation constant of the salt.Upon dissolution and dissociation, the environmental fate and behavior the nickel ion and associated anion can be measured or estimated within the environmental compartments (water, air, sediment and soil). For metals and sparingly soluble metal compounds, the transformation/dissolution protocol (T/DP, OECD 29) is designed to determine the rate and extent to which metals and SSMCs can produce soluble available ionic and other metal-bearing species in aqueous media under a set of standard laboratory conditions representative of those generally occurring in the environment. Once determined, this information can be used to evaluate the short-term and long-term aquatic toxicity of the metal or sparingly soluble metal compound from which the soluble species came.

Physicochemical and ecotoxicological data for the nickel ion is therefore essential to understanding the environmental fate and toxicological characteristics of the nickel metal, compounds, and SSMCs. Data for the metal ions can be represented by fate and toxicity data generated with simple metal salts (e.g., chloride or nitrate salts). For example, the potential hazards associated with nickel metal can be estimated by 1) measuring the rate and extent of the release of nickel ions from nickel metal using the T/DP test; and, 2) through the evaluation of the nickel free ion tested using a soluble nickel compound (e.g., nickel chloride). Thus, data for each individual nickel compounds or SSMC and the individual metal can be used to “read-across” to characterize the hazard of another nickel compound.