Nitriles, C12-18

Endpoint summary

Additional information

Alkylnitriles are produced at different EU manufacturing sites. They are produced and used as intermediate under strictly controlled conditions only. Consequently, no significant exposures are anticipated, and no risk assessment needs to be performed.

With alkylnitriles substances are meant consisting of a linear alkyl chain with a nitrile, with a common structure of CH₃- [CH₂]_n- C≡N where n is between 10 (Dodecanenitrile) and 16 (Octadecanenitril). As the alkylchains are derived from natural vegetable fatty acids, some level of unsaturation can be present, e.g. for Oleylnitrile (9-Octadecenenitrile).
As these substances share the same chemical structure, and only differ in the length of the alkyl chain, which shows great overlap between them, they will share the same chemical reactivity and have greatly similar physico-chemical properties. So are all alkylnitriles practically insoluble in water and their log Pow values are all around 5 (5.00 for C12-fraction in coconitrile and 5.08 for C18-fraction in tallownitrile).
Consequently, their toxicological profiles will be greatly similar, where the difference of chain length can possibly play a modifying factor for their bio-availability. It is assumed that the shorter chain lengths are possibly somewhat more bio-available. Consequently, toxicological information from one alkylnitriles is of relevance for the evaluation of the others. Specifically with respect to the shorter chain alkyl nitrile, for which its toxicological results possibly represent a worst case value for alkylnitriles with longer chain lengths.

The common name for C12-18 (even numbered) nitriles is Coconitrile.

Toxicological profile

The acute oral toxicity of the Coconitrile is low, with no mortality being observed up to levels of 5000 mg/kg body weight. Also comparable other nitriles as Tallownitrile and Oleylnitrile showed no mortality up to highest tested dose of 5000 mg/kg body weight. The acute oral toxicity of the Coconitrile is low, with no mortality being observed up to levels of 5000 mg/kg body weight. Alkylnitriles are irritating to the skin, but are not irritating to eyes. A GPMT study with Coconitrile indicates no concern for sensitisation.

Repeated dose administration with the structural analogue Dodecanenitrile (which is the main constituent of Coconitrile) also showed comparatively low toxicity with a NOAEL of 50 mg/kg bw/d from a combined 28-day/reproduction screening study. At 250 mg/kg bw/d animals pushed their heads through the bedding starting on day 4 of mating, indicating discomfort after administration of the test item. No other clinical signs or signs of discomfort were noted. Other findings at 250 mg included lymphoid atrophy in lymphoid organs as well as the hypertrophy of the adrenal glands indicating stress and histopathological ulcerations and erosions in the stomach, possibly promoted by the stress. At the higher dose level of 1000 mg/kg effects were more severe and included lower food consumption and body weight gain, increase of liver weight and mortality in females during and directly after giving birth. The same study also did not indicate a concern for reproductive or developmental toxicity.

Genotoxicity: Alkylnitriles do not react with DNA or protein, and bacterial mutagenicity studies with Coconitrile and various other alkylnitriles do not indicate a concern for mutagenicity. Additionally, a mammalian chromosomal aberration study with Dodecanenitrile also does not indicate any genotoxic potential.Based on the lack of genotoxicity and lack of specific organ toxicity in the repeated dose studies, carcinogenic effects are not likely.

Toxicokinetics, metabolism and distribution

Although direct experimental data concerning inhalative, dermal or oral absorption are not available for alkylnitriles, an indication for possible absorption can however be deduced from the physico-chemical properties of these substances and from results of toxicological investigations.

Inhalation: Alkylnitriles are practically insoluble in water and log Pow values for these materials are around 5 (5.00 for C12-fraction in coconitrile and 5.08 for C18-fraction in tallownitrile). Vapour pressure is low (1.8 Pa at 20°C for Coconitrile and < 1 Pa for Dodecanenitrile (Boublik T et al, 1984, from EpiWin)). With regard to potential respiratory exposure, a very low vapour pressure can be assumed for the group of Alkylnitriles as with increasing chain-length the vapour pressure drops significantly. Taken together, based on physico-chemical properties and conditions of use, a low respiratory bioavailability can be anticipated.

Dermal: Based on the very low water solubility and relative high Pow of 5 rate of transfer to epidermis is probably limited. However, the molecular size is not large and high Pow favours uptake in stratum corneum. As worst case, 100% dermal absorption is assumed.

Oral: Being a fatty acid derived molecule, uptake after oral exposure could be mediated by micellular solubilisation by bile salts. The observed increase of liver weight observed at the highest dose in the repeated dose study of Dodecanenitrile is indicative of liver metabolism following gastro-intestinal uptake. In addition, the alkylnitriles satisfy the Lipinski rule indicating likely bioavailability. As worst-case, a value of 100 % oral absorption is assumed.

 

Available biodegradation studies with alkylnitriles indicate that all members of this category are readily biodegradable. For such substance it can then be assumed that mammals are also capable of metabolisation. Also the OECD Toolbox liver metabolism simulator indicates possible liver metabolism, which is also suggested by the observed increase of liver weights at the highest dose levels in the repeated dose study with dodecanenitrile.

Although highly lipophilic substances (log P >4), the repeated dose administration with Dodecanenitrile does not provide an indication for bioaccumulation for these alkylnitriles.