Bismuth(3+) neodecanoate

Endpoint summary

Description of key information

Based on the solubility of bismuth (3+) neodecanoate in water, a complete dissociation resulting in bismuth cations and neodecanoate anions may be assumed under environmental conditions. Thus, the environmental fate of bismuth (3+) neodecanoate in the environment is most accurately evaluated by separately assessing the fate of its constituents bismuth and neodecanoate. Data available for the bismuth cation and the neodecanoate anion indicate that abiotic and biotic degradation in respective compartments do not contribute significantly to its fate in the environment.

 

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.

Neodecanoic acid:

Abiotic degradation is not considered to significantly affect the environmental fate of neodecanoic acid since neodecanoic acid is lacking hydrolysable functional groups and does not absorb light within a range of 290 to 750 nm. Neodecanoic acid is not readily biodegradable (11% biodegradation in 28 d) based on results from a standard OECD ready biodegradation test. Studies are not available to assess the biodegradability of neodecanoic acid under simulated conditions or in soil, but given the limited biodegradation in water, biodegradation under simulated conditions, or in soil is not expected to occur to a great extent.

Transport and distribution: The estimated Koc of neodecanoic acid is 121 and may be sensitive to pH. The vapor pressure is very low, i.e. 0.65 Pa suggesting a limited volatilization from soil. Henry’s Law constant for neo-decanoic acid is calculated with 0.54 Pa-m3/mole at 25 °C indicating that volatilization from water is not expected to occur at a rapid rate, but may occur. Neodecanoic acid is a weak organic acid with an estimated dissociation constant (pKa) of 4.69. Consequently, neodecanoic acid, at neutral pH, typical of most natural surface waters, is expected to dissociate to the ionised form and therefore to remain largely in water.

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 (3+) neodecanoate in water, a dissociation resulting in bismuth cations and neodecanoate anions may be assumed under environmental conditions. The ions of bismuth (3+) neodecanoate are considered a hard acid and a hard base, respectively. 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 (3+) neodecanoate 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 (3+) neodecanoate 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 (3+) neodecanoate, bismuth (3+) ions are expected to form insoluble salts that reduce its bioavailability whereas neodecanoate anions remain dissolved in the water column.

 

Thus, read-across to bismuth cations and neodecanoate anions is applied since the dissociation products of bismuth (3 +) neodecanoate 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 (3+) neodecanoate, information on the assessment entities bismuth cations and neodecanoate 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 (3+) neodecanoate.

 

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.