Bismuth hydroxide nitrate oxide

Endpoint summary

Additional information

General discussion of environmental fate and pathways:

 

Environmental Fate

The test substance, bismuth subnitrate, is a solid under all environmental conditions and is moderately soluble in water (900.7 mg/L). It has a low vapour pressure (0.00011 Pa at 20°C) therefore any environmental release will result in little release directly to the atmosphere.

 

For metals and inorganic substances like bismuth subnitrate, the concept of degradability as applied to organic compounds has limited or no meaning. Very limited information is available on the chemistry of Bi in the environment. Bismuth can exist under the following oxidation states: 0, +III and +V. No information on measured Bi-speciation in water is available, and it will be assumed that Bi3+ is the dominant species under the prevalent environmental conditions. A Pourbaix diagram, showing the oxidation state and major species of bismuth as a function of pH and reduction potential indeed predicts that trivalent Bi is dominant under conditions commonly found in oxic fresh waters, i. e., pH between 5 and 9; redox potential [Eh] between 0.5 and 1 V. It is assumed that upon dissolution of bismuth substances, the environmental conditions control the (redox) speciation of bismuth in water, soil and sediment, regardless of the Bi compound added.

Substances containing nitrate ions are known to play an important role in the nutrient enrichment of surface waters, commonly called eutrophication. Eutrophication waters have elevated nutrient concentrations, which stimulate the growth of certain algal species. The oxygen concentration in water will generally decrease influencing other organisms, such as most fish species leading to a negative effect on the biodiversity of the ecosystem. As eutrophication is a common effect due to an excess in nitrate in the environment, this is covered in European Regulations. The Directive 2000/60 of the European parliament and of the council of 23 October 2000 establishing a framework for Community action in the field of water policy and the Council Directive 91/676/EEC of 12 December 1991 concerning the protection of waters against pollution caused by nitrates from agricultural sources are both European Regulations regulating the emission and concentration of nitrate substances in the environment. All nitrate waste from the manufacture of bismuth subnitrate is transferred to a local municipal facility for processing and substrate removal prior to release to STP.

Adsorption to soil is predicted to be low, based on the estimated low log Koc value (1.3 to 1.5) for the substance, however, log Kp values for elemental bismuth reported in the literature are higher: log Kp (solids-water in suspended matter) = 5.66, log Kp (solids-water in sediment) = 3.84, log Kp (solids-water in soil): 2.83. The risk of significant exposure related effects to sediment and soil dwelling organisms is considered to be low as strict risk management measures are in place to ensure that release of the substance or product to the environment is minimised.

 

Because of the low solubility of bismuth subnitrate in the relevant aquatic test media at pH values between 6.0 and 7.9 after equilibration for 7 days, it can be concluded that the bioavailability of bismuth in the aquatic environment is low and that there is low potential for bioaccumulation of bismuth.

 

Based on the available data on toxicity of bismuth to birds, the dietary toxicity of bismuth is considered minimal (NOEC ≥ 1000 mg bismuth/kg food) and hence, it can be assumed that there is little concern on secondary poisoning of bismuth to higher organisms through the aquatic food chain. Also, bismuth subnitrate demonstrates low acute toxicity in mammalian studies therefore in the event of exposure to environmental organisms, effects due to secondary poisoning can be excluded.