Docosyl acrylate

Endpoint summary

Description of key information

Gastro-intestinalI-, respiratory- and dermal absorption of docosyl acrylate to a major extent is not expected due to physico chemicaproperties (log Pow: 11.2; water solubility: < 0.1 mg/L, molecular weight: 380.64 g/mol).
In addition, bioaccumulation is unlikely due to a very limited absorption of the substance.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - dermal (%):

0.26

Additional information

Read across has been done to a dataset of suitable congeners of the family of acrylate esters, mainly to a mixture of Behenyl acrylates (C18-C22). The substance to be registered (docosyl acrylate, C22) was part of this mixture.

Docosyl acrylate is solid at room temperature with a molecular weight of 380.64 g/mol and an absolute density of 0.86 g/cm³ at 25°C. The substance has a melting point of 30 °C. A water solubility for docosyl acrylate of < 0.1 mg/L (20 °C) and a log Pow of 11.2 (25 °C) were determined. The vapour pressure was estimated to be 0.000035 mbar (25 °C).

Absorption:

Based on the molecular weight, the high log Pow and a low water solubility, Docosyl acrylate is not very likely to be absorbed in the GI tract. The log Pow of 11.2 indicates that it will not diffuse well across plasma membranes. In addition, gastro-intestinal absorption of Docosyl acrylate will not be triggered by passage via passive diffusion through aqueous pores or carriage with the bulk passage of water, which is favoured for small (molecular weight < 200 g/mol), water soluble substances.

The substance may be taken up by micellular solubilisation since this mechanism may be of particular importance for highly lipophilic compounds (log Pow > 4), particularly those that are poorly soluble in water. Overall, limited gastrointestinal absorption is expected for Docosyl acrylate based on its physicochemical properties. Moreover, almost no systemic effects were seen in acute and repeated dose toxicity studies after oral administration of a read across substance (mixture of long-chain acrylates) demonstrating and supporting that Docosyl acrylate is not very well absorbed in the gastrointestinal tract, and if absorbed reveals a low systemic toxicity.

As Docosyl acrylate is a solid with very low water solubility (< 0.1 mg/L), a molecular weight of 380.5 g/mol and a log Pow of 11.2, dermal absorption is expected to be very low. In addition, Docosyl acrylate showed no effects when tested for acute dermal toxicity.

These characteristics are in line with information obtained with a read across substance Lauryl methacrylate:

Experiments on the read across substance Dodecyl methacrylate (Lauryl methacrylate) with rat skin have demonstrated that the long-chain methacrylate esters in principle are dermally absorbed at very low amounts (0.26 % over 26 h). As a tendency confirmed with experiments on esters up to a chain length of C8, absorption decreased with increasing ester chain length. Due to the slow diffusion and the metabolic competency of the skin, the ester underwent complete hydrolysis to methacrylic acid and the long-chain alkyl alcohol.

Docosyl acrylate exhibits a low volatility (vapour pressure of 0.000035 mbar). Therefore, only a very minimal amount of the substance is available for inhalation and thus, absorption by inhalation can be almost excluded. In addition, fine dust is not formed by this compound. Consequently, inhalation exposure due to fine dust or particles is also unlikely.

Distribution and metabolism:

Based on the physicochemical properties (molecular weight: 380.5 g/mol, log Pow: 11.2, water solubility: < 0.1 mg/L) Docosyl acrylate is unlikely to be widely distributed systemically throughout the extracellular compartments of the body after absorption. Particularly due to the low water solubility and the high log Pow value above 10, a long biological half-life in tissues could be expected, but is almost excluded due to the poor absorption. Thus, Docosyl acrylate has no bioaccumulation potential.

The metabolism is determined by physicochemical factors like electronic and steric effects within the molecule and/or by the presence of functional groups. Phase II conjugation reactions like glucuronidation or sulfatation might occur subsequent to Phase I reaction, e.g. after introduction of a OH-group via Cytochrome P450 mediated oxidation.

Esters are supposed to be rapidly hydrolysed in local tissues as well as in blood by carboxyl esterases (high activity within many tissues and organs like liver, GI tract, nasal epithelium and skin) forming acrylic acid and the respective alcohol. However, the kinetics strongly depends on water solubility. In addition, it cannot be excluded that the long C-chain might hinder the enzyme to access to the ester bound. There is a trend towards increasing half-life of the esters in blood with increasing alcohol chain length. Nevertheless for all acrylate esters a relatively fast hydrolysis can be assumed. But systemically absorbed parent esters will be effectively removed during first pass through the liver resulting in their relatively rapid elimination from the body. The primary metabolite acrylic acid is subsequently cleared rapidly from blood and this metabolism occurs by standard physiological pathways with the majority being exhaled as CO2. The respective alcohol is also predominantly cleared via the liver. In the organism, the acid is further metabolised via the valine pathway of the citric acid cycle. The alcohol will be further metabolised by the two standard metabolic pathways for fatty alcohols.

Consequently effects observed are linked to the hydrolysis products: alcohols and acrylic acid. The alcohols are considered of low toxicity especially the unbranched long-chain ones, as those follow the metabolic pathways of fatty nutritional substrates (e.g. fatty acids). The other metabolite acrylic acid is identical for all esters.

Generally, metabolism will render the molecule more polar and harmless, leading to faster excretion. No conversion into a metabolite that is more toxic than the parent is expected as no increases in toxicity where noted in the presence of metabolic activation during the in vitro tests.

Excretion:

The relatively low water solubility and the molecular weight (> 200 g/mol) indicate that renal excretion is not a relevant route of systemically available Docosyl acrylate. Excretion might occur predominantly via the faecal route.

Summary:

The above TK information derived by taking into account a basic data set which includes mainly physico-chemical data, and data like skin irritation/corrosion, eye irritation, skin sensitization, in vitro mutagenicity, acute oral toxicity, short-term and repeated dose toxicity enable qualitative judgments of the TK behavior of Docosyl acrylate.

It can be concluded that gastro-intestinaI-, respiratory- and dermal absorption of Docosyl acrylate to a major extent is not expected due to its physico-chemical properties (log Pow: > 11; water solubility: < 0.1 mg/L, molecular weight: 380.5 g/mol).

In addition, bioaccumulation is unlikely due to a very limited absorption of the substance.