Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

General discussion of environmental fate and pathways:

 

Environmental Fate

The test substance, bismuth citrate, is a solid under all environmental conditions and is only slightly soluble in water (10.97 to 53.81 mg/L). It has a low vapour pressure (0.00012 Pa at 20°C) therefore any environmental release will result in little release directly to atmosphere.

The bismuth component of bismuth citrate cannot be biodegraded. For metals, the concept of degradability as applied to organic compounds has limited or no meaning. By read-across from citric acid, the citrate component of bismuth citrate is considered to be readily biodegradable. Very limited information is available on the chemistry of bismuth 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 bismuth compound added.

 

Adsorption to soil is predicted to be low, based on the estimated low log Koc value (1.0) 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 read-across substance, 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 Bi/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 citrate demonstrates low acute toxicity in mammalian studies therefore in the event of exposure to environmental organisms, effects due to secondary poisoning can be excluded.