Bismuth tris(2-ethylhexanoate)

Endpoint summary

Description of key information

Based on the solubility of bismuth tris(2-ethylhexanoate) in water, a complete dissociation resulting in bismuth and 2-ethylhexanoate ions may be assumed under environmental conditions. Thus, the environmental fate of bismuth tris(2 -ethylhexanoate) in the environment is most accurately evaluated by separately assessing the fate of its constituents bismuth and 2-ethylhexanoate.In the assessment of environmental fate and behaviour of bismuth tris(2-ethylhexanoate), data available for the bismuth cation and the 2-ethylhexanoate anion indicate that abiotic degradation in respective compartments does not contribute significantly to its fate in the environment. However, 2-ethylhexanoate is readily biodegradable.

Bismuth

Abiotic degradation (e.g. hydrolysis) is not relevant for inorganic substances, including bismuth, that are assessed on an elemental basis. Bismuth as an element is not considered to be (bio)degradable.

Transport and distribution: Partition coefficients for bismuth in soil, sediment and suspended matter range from Log Kp of 2.83 to 5.66 L/kg dw. Hence, bismuth is not expected to be mobile under most environmental conditions.

2-ethylhexanoic acid

Abiotic degradation may affect the environmental fate of 2-ethylhexanoic acid since it is prone to slow degradation by photochemical processes. Hydrolysis, however, is not expected to be an important fate path.

Biotic degradation: 2-ethylhexanoate is readily biodegradable. Based on the biodegradation in water, biodegradation in soil and sediment is also expected to occur to a greater extent.

Bioaccumulation: 2-ethylhexanoate has a low potential for bioaccumulation (logPow = 2.96)

Transport and distribution: Based on modelling, 2-ethylhexanoate will preferentially distribute into water and has a low potential for volatilisation. A significant adsorption to soil solid phases or sediment is not expected.

Additional information

Read-across approach

 

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion. Based on the solubility of bismuth tris (2-ethylhexanoate) in water, a dissociation resulting in bismuth cations and 2-ethylhexanoate anions may be assumed under environmental conditions. Bismuth carboxylates were analysed for the presence of covalent and ionic bonds between bismuth and the oxygen of the carboxylate group. It was confirmed that bismuth carboxylate bonds are ionic (Mehrotra and Bohra 1983). The equilibrium equation of the dissociation products does not indicate any pH dependency of the dissociation. The dissociation of bismuth tris(2-ethylhexanoate) is in principle reversible and the ratio of the salt /dissociated ions is dependent on the metal-ligand complexation constant of the salt, the composition of the solution and its pH.

 

A metal-ligand complexation constant of bismuth tris(2-ethylhexanoate) could not be identified. Data for bismuth appear to be generally limited. However, bismuth cations tend to form complexes with ionic character as a result of their low electronegativity. Further, the ionic bonding of bismuth is typically described as resulting from electrostatic attractive forces between opposite charges, which increase with decreasing separation distance between ions. Bi3+ cations are acidic and have a strong tendency to form insoluble salts (hydroxides) in water reducing its bioavailability (reference given in HSDB, 2008; Thomas et al. 1984; Thomas, 1991). Further insoluble bismuth salts include oxides, sulphides and oxychlorides, salts of inorganic oxoacids (carbonate, nitrate, sulfate) and organic acids (triglycollate, trialkylates) (Fowler and Vouk, 1979). However, uncertainties regarding the behaviour of bismuth species in aqueous solutions remain (Slikkerveer and De Wolff, 1996 and references therein). Upon dissolution of bismuth tris(2-ethylhexanoate), bismuth (3+) ions are expected to form insoluble salts that reduce its bioavailability whereas 2 -ethylhexanoate anions remain dissolved in the water column.

 

Thus, read-across to bismuth cations and 2 -ethylhexanoate anions is applied since the dissociation products of bismuth 2 -ethylhexanoate behave differently in the environment regarding their fate and toxicity. A separate assessment of each assessment entity is performed. Please refer to the data as submitted for each individual assessment entity.

 

In order to evaluate the environmental fate of bismuth tris(2-ethylhexanoate), information on the assessment entities bismuth cations and

2-ethylhexanoate anions were considered. For a documentation and justification of that approach, please refer to the separate document attached to section 13, namely Read Across Assessment Report for bismuth tris(2-ethylhexanoate).

References:

Mehrotra, R. C. and Bohra R. (1983): Metal Carboxylates. Academic Press

HSDB (2008). Hazardous substances data bank (HSDB), a database of the national library of medicine’s TOXNET system.

Fowler, B. A. and Vouk, V. (1979). Chapter 20, Bismuth, in Handbook on the Toxicology of Metals, Friberg et al. (Edt), Elsevier, North-Holland Biomedical Press.

Slikkerveer, A. and De Wolff, F. (1996). Chapter 27, Toxicity of Bismuth and Its Compounds, CRC Press, Inc., p. 439-454.

Thomas, D.W., Hartley, T. F. and Coyle, P. (1984), II.5 Bismut, Met. Umwelt, Adelaide, p. 343-350. Krieger, R. (Ed.) (2001). Bismuth, Handbook of pesticide toxicology, p. 1389-1390.

Thomas, D. W. (1991). II.5 Bismuth, Met. Their Comp. Environ., p. 789-801.