2-[[(butylamino)carbonyl]oxy]ethyl acrylate

Endpoint summary

Description of key information

In accordance with Annex VIII, Column 1, Item 8.8.1, of Regulation (EC) 1907/2006 and ‘Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance’ (ECHA, 2017), an assessment of the toxicokinetic behaviour of the target substance is conducted to the extent that can be derived from the relevant available information. This comprises a qualitative assessment of the available substance specific data on physicochemical properties.

Based on the qualitative assessment the test substance is considered to be readily absorbed via the inhalation route. Dermal absorption is considered to be moderate to high. Data on acute as well as repeated dose oral toxicity indicate that oral absorption might occur. The test substance may have a low potential to accumulate in the body. The test substance is expected to undergo enzymatic hydrolysis in the gastrointestinal tract and hydrolysis products will be widely distributed in the body before they may be metabolised in the liver. Unabsorbed test substance will be excreted via the faeces while conjugated metabolites will be excreted via urine.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

Toxicokinetic statement of 2-(butylcarbamoyloxy)ethyl prop-2-enoate

There are no experimental studies available in which the toxicokinetic behaviour of 2-(butylcarbamoyloxy)ethyl prop-2-enoate was investigated.In accordance with Annex VIII, Column 1, 8.8.1, of Regulation (EC) 1907/2006 and with ‘Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance’ (ECHA, 2017), an assessment of the toxicokinetic behaviour of 2-(butylcarbamoyloxy)ethyl prop-2-enoate was conducted to the extent that can be derived from the relevant available information. This comprises a qualitative assessment of the available substance specific data on physico-chemical and toxicological properties according to Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance (ECHA, 2017) and taking into account further available information on structural analogue substances.

Physico-chemical properties

In its pure state, 2-(butylcarbamoyloxy)ethyl prop-2-enoate is a clear light yellow liquid with a water solubility of 4.99 g/L at 20 °C. The substance has a molecular weight of 215.2463 g/mol. The octanol/water partition coefficient (log Pow) was calculated to be 1.82 (QSAR calculation) and the vapour pressure was estimated to be ≤ 129 Pa at 25 °C (QSAR calculation). 

Absorption

Absorption is a function of the potential for a substance to diffuse across biological membranes. The most useful parameters providing information on this potential are the molecular weight, the octanol/water partition coefficient (log Pow) value and the water solubility. The log Pow value provides information on the relative solubility of the substance in water and lipids (ECHA, 2017).

Oral

In general, molecular weights below 500 and log Pow values between -1 and 4 are favourable for absorption via the gastrointestinal (GI) tract, provided that the substance is sufficiently water soluble (> 1 mg/L). Lipophilic compounds may be taken up by micellar solubilisation by bile salts, but this mechanism may be of particular importance for highly lipophilic compounds (log Pow > 4), in particular for those that are poorly soluble in water (≤ 1 mg/L) as these would otherwise be poorly absorbed (ECHA, 2017).

As the molecular weight of 2-(butylcarbamoyloxy)ethyl prop-2-enoate is 215.2463 g/mol, oral absorption in the gastrointestinal (GI) tract is considered possible. Additionally, the water solubility of 4.99 g/L and the log Pow value of 1.68 suggest the substance will be readily absorbed from the GI tract.

The available data on acute oral toxicity indicate the substance has low acute toxicity. However, since adverse effects were observed oral absorption might occur.

In a first step of an acute oral toxicity study performed with a starting dose of 5000 mg/kg bw 2-(butylcarbamoyloxy)ethyl prop-2-enoate sunflower oil as vehicle administered via gavage 1/1 female rat died. Decreased activity, disturbance of coordination (abnormal gait), decreased righting- and plantary reflex, decreased muscular tension (grip- and limb tone, body tone, abdominal tone) and disturbance of the autonomic functions (piloerection) were observed between 1 and 4 h after administration while macroscopic examinations at necropsy did not reveal any treatment-related abnormalities. Thus, a second test with a dose level of 2000 mg/kg bw was performed. No mortality and no clinical signs or effects on body weight and no abnormal pathological findings were observed in 3/3 female rats. In a third step administration of 2000 mg/kg bw was repeated in 3 female rats. Although no clinical signs or effects on body weight and no abnormal pathological findings were observed in 3/3 females, 1/3 female was found dead on Day 7 (Mácsai Kuthy, 2015).

Data of a subacute oral repeated dose toxicity study combined with a reproductive/developmental toxicity screening test indicate that oral absorption of the test substance might occur. The test substance was administered orally via gavage to male and female rats at doses of 0 (vehicle only), 100, 300 or 600 mg/kg bw/day before and during mating as well as after mating (altogether 49 and 55 days for males and females, respectively). Reversibility of any effects observed was assessed following a 14 day recovery period in additional animals of the control and high dose group. At the lowest dose (100 mg/kg bw/day) no treatment-related changes in any of the parameters were observed. An oral dose of 300 mg/kg bw/day induced clinical signs (salivation and nuzzling up the bedding material) as well as pathological changes in the forestomach (thickened mucous membrane, squamous cell hyperplasia). Food consumption and hematology parameters were not affected at this dose. Premature death of one male animal occurred at the highest dose (600 mg/kg bw/day). Clinical signs (salivation, nuzzling up and compulsive biting of the bedding material, prone position, closed eyes), slightly reduced body weight gain, decreased food consumption, changes in white blood cell parameters as well as lesions in the stomach (thickened mucous membrane; adhesion to the liver) were observed in surviving animals at 600 mg/kg bw/day. The lesions in the stomach were persistent in male rats until the end of the recovery period. Histopathological alterations in the forestomach in both sexes at 600 mg/kg bw/day (ulceration, necrosis or squamous cell hyperplasia) were reversible as no pathological changes were observed in the recovery groups. Since the (fore)stomach represents the first site of contact test substance related effects might be reduced to local effects. Clinical signs, reduced body weights, decreased food consumption and changes in the white blood cell count might be secondary to the observed local effects. However, oral absorption of the test substance cannot be excluded.

The potential of a substance to be absorbed in the GI tract may be influenced by chemical changes taking place in GI fluids as a result of metabolism by GI flora, by enzymes released into the GI tract or by hydrolysis. These changes will alter the physicochemical characteristics of the substance and hence predictions based upon the physico-chemical characteristics of the parent substance may no longer apply or apply to a lesser extent (ECHA, 2017). With regard to 2-(butylcarbamoyloxy)ethyl prop-2-enoate it seems to be likely that it will be hydrolysed in the GI tract and that the cleavage products could be absorbed. The ester bonds may be hydrolysed in the GI tract by esterases to form the corresponding alcohol and acid moieties. The rate of hydrolysis is unknown. The smaller molecules of the alcohol and acid moieties are likely to be absorbed faster than the parent molecule. Potential metabolites calculated by OECD QSAR toolbox v. 3.3 indicate that 2-(butylcarbamoyloxy)ethyl prop-2-enoate will be hydrolysed via enzymatic hydrolysis or acidic/basic or neutral hydrolysis. For these cleavage products it is anticipated that they will be absorbed in the GI tract due to their smaller size and potentially increased water solubility.

Dermal

The dermal uptake of liquids and substances in solution is higher than that of dry particulates, since dry particulates need to dissolve into the surface moisture of the skin before uptake can begin. Molecular weights below 100 g/mol favour dermal uptake, while for those above 500 g/mol the molecule may be too large. Dermal uptake is anticipated to be low if the water solubility is < 1 mg/L; low to moderate if it is between 1-100 mg/L; and moderate to high if it is between 100-10000 mg/L. Log Pow values in the range of 1 to 4 (values between 2 and 3 are optimal) are favourable for dermal absorption, in particular if the water solubility is high. For substances with a log Pow above 4, the rate of penetration may be limited by the rate of transfer between the stratum corneum and the epidermis, but uptake into the stratum corneum will be high. Log Pow values above 6 reduce the uptake into the stratum corneum and decrease the rate of transfer from the stratum corneum to the epidermis, thus limiting dermal absorption (ECHA, 2017).

The physico-chemical properties of the target substance 2-(butylcarbamoyloxy)ethyl prop-2-enoate indicate that dermal absorption of the molecule is likely. There is no experimental data on the effects of acute or long-term dermal exposure to the target substance.

The dermal permeability coefficient (Kp) can be calculated from log Pow and molecular weight (MW) applying the following equation described in US EPA (2004):

log(Kp) = -2.80 + 0.66 log Pow – 0.0056 MW

QSAR calculations regarding the molecular weight, log Kow and water solubility, estimated the following dermal absorption rates (calculated with DERMWIN, v.2.01, 2011, modified considering the Fick´s first law): 1.57 × 10-3 cm/h. Considering the water solubility (4.99 mg/L), the dermal flux is estimated to be 7.83 µg/cm²/h. This indicates a medium high dermal absorption potential. Usually, this value is considered as indicator for a dermal absorption of 40% (Mostert and Goergens, 2011). Therefore, the calculated dermal uptake indicates that 2-(butylcarbamoyloxy)ethyl prop-2-enoate has a medium to high potential for dermal absorption.

If a substance shows skin irritating or corrosive properties, damage to the skin surface may enhance penetration. There is no in vivo data on the effects of acute or long-term dermal exposure to 2 -(butylcarbamoyloxy)ethyl prop-2-enoate and no in vivo data on skin irritating or corrosive properties of the target substance. The available in vitro skin irritation and skin corrosion data do not show skin irritating effects (Ágh, 2014 and 2015). In the skin sensitisation study (LLNA) performed on the mouse with the test substance slight to moderate swelling increasing to severe and a slight erythema was observed at the dosing sites. Thus, an enhanced penetration of the substance due to local skin damage cannot be excluded. Furthermore, 2-(butylcarbamoyloxy)ethyl prop-2-enoate was identified as a skin sensitiser, which shows that some uptake must have occurred, although it may only have been a small fraction of the applied dose.

Taking all the available information into account, the dermal absorption potential of the test substance is considered to be moderate to high.

Inhalation

Substances with low volatility have a vapour pressure of less than 0.5 kPa or a boiling point above 150 °C (ECHA, 2017). With an estimated vapour pressure of ≤ 129 Pa at 25 °C and a boiling point > 150 °C (decomposition at 180 °C before reaching the boiling point) 2-(butylcarbamoyloxy)ethyl prop-2-enoate is a liquid with low volatility. Consequently, under normal use and handling conditions, inhalation exposure and availability for respiratory absorption of the substance in the form of vapour, gases or mists is not significant (ECHA, 2017). However, the substance may be available for absorption after inhalation of aerosols, if the substance is sprayed (e.g. as a formulated product). In humans, particles with aerodynamic diameters below 100 μm have the potential to be inhaled. Particles with aerodynamic diameters below 50 μm may reach the thoracic region and those below 15 μm the alveolar region of the respiratory tract. Particles deposited in the nasopharyngeal/ thoracic region will mainly be cleared from the airways by the mucocilliary mechanism and swallowed. With a moderate log Pow value of 1.68 the substance will be readily absorbed directly across the respiratory tract epithelium by passive diffusion.

The systemic signs of toxicity present in available acute inhalation toxicity studies indicate that absorption has occurred. In a first study performed with the test substance containing > 83.6% of the main compound the acute inhalation toxicity was determined in groups of 6 rats (3 males and 3 females) according to OECD 436 via nose only treatment using an aerosol generated from the undiluted test substance. The animals were exposed to test substance concentrations of 0.52, 1.05 and 5.06 mg/L air for 4 h and observed for a period of 14 days following administration. At concentrations of 5.06 and 1.05 mg/L air clinical signs such as moderately reduced motility, moderate ataxia, slight tremor, severe dyspnoea, lacrimation and vocalisation were observed in all males and females. All of these animals died prematurely within 24 h after administration. For all animals treated with a concentration of 0.52 mg/L air the following clinical signs were observed: slightly reduced motility, slight ataxia, slight tremor, moderate dyspnoea, lacrimation and vocalisation. Necropsy revealed effects to the target (oedematous or emphysematous lungs) in all test substance treated animals. In addition the acute inhalation toxicity of the test substance containing ≤ 83.6% of the main compound was determined under the same conditions at concentrations of 1.06 and 5.12 mg/L air. At a concentration of 5.12 mg/L air clinical signs such as moderately reduced motility, moderate ataxia, slight tremor, severe dyspnoea, abdominal position, lacrimation and vocalisation were observed in all males and 2/3 females. One female died during inhalation. All further animals died prematurely within 24 h after administration. For all animals treated with a concentration of 1.06 mg/L air slight dyspnea was observed. No mortality occurred at this concentration. Necropsy revealed oedematous and haemorrhagic lungs in all animals and haemorrhage in the thorax in 1/3 males at 5.12 mg/L air. Oedematous lungs were observed in all animals at 1.06 mg/L air. Due to the equivocal results the determination of the acute inhalation toxicity of the test substance containing > 83.6% of the main compound was repeated in a further approach. Another 6 rats (3 males and 3 females) were exposed to test substance concentrations of 0.54 and 1.08 mg/L air under the same conditions. At concentrations of 1.08 mg/L air clinical signs such as moderately reduced motility, moderate ataxia, moderate to severe dyspnoea, lacrimation and vocalisation were observed in all females and 2/3 males immediately to 3 h after administration. One male died during inhalation. All further animals died prematurely within 24 h after administration. For all animals treated with a concentration of 0.54 mg/L air slightly reduced motility and slight ataxia was observed immediately to 3 h after administration and slight dyspnoea was observed immediately after administration until test day 3 in all male and female rats. No mortality occurred at this concentration. Necropsy revealed oedematous lungs in all animals at 1.08 mg/L air. No pathological findings were observed in all animals at 0.54 mg/L air.

 

Thus, taking all the available information into account, it is considered that the test substance will be readily absorbed via the inhalation route.

Distribution and accumulation

Distribution within the body through the circulatory system depends on the molecular weight, the lipophilic character and water solubility of a substance. In general, the smaller the molecule, the wider is the distribution. Small water-soluble molecule and ions will diffuse through aqueous channels and pores. The rate at which very hydrophilic molecules diffuse across membranes could limit their distribution. If the molecule is lipophilic (log Pow > 0), it is likely to distribute into cells and the intracellular concentration may be higher than extracellular concentration particularly in fatty tissues. Furthermore, the concentration of a substance in blood or plasma and subsequently its distribution is dependent on the rates of absorption (ECHA, 2017).

The clinical signs observed in the acute inhalation toxicity studies indicate that the target substance is systemically available. The macroscopic examination during necropsy did not show any target organ besides the lung.

In general, lipophilic substances tend to concentrate in adipose tissue, and depending on the conditions of exposure may accumulate. Although there is no direct correlation between the lipophilicity of a substance and its biological half-life, it is generally the case that substances with high log Pow values have long biological half-lives. Substances with log Pow values of 3 or less would be unlikely to accumulate with the repeated intermittent exposure patterns normally encountered in the workplace but may accumulate if exposures are continuous (ECHA, 2017). The log Pow of 1.68 implies that 2-(butylcarbamoyloxy)ethyl prop-2-enoate may have a low potential to accumulate in adipose tissue.

As discussed under oral absorption, 2-(butylcarbamoyloxy)ethyl prop-2-enoate is expected to undergo enzymatic hydrolysis in the GI tract prior to absorption. After being absorbed, the hydrolysis products are expected to be widely distributed due to the relatively small size and the functional groups, which are characteristics that increase the water solubility. The substances absorbed from the GI tract will be transported via the portal vein to the liver, where further metabolism can take place. Substances that are absorbed through the pulmonary alveolar membrane or through the skin enter the systemic circulation directly before transport to the liver where metabolism will take place.

Metabolism

No data are available regarding metabolism. Prediction of compound metabolism based on physicochemical data is very difficult. Structure information gives some but no certain clue on reactions occurring in vivo. The potential metabolites following enzymatic metabolism were predicted using the QSAR OECD toolbox (v3.3.0.152, OECD, 2014). This QSAR tool predicts which metabolites may result from enzymatic activity in the liver and by intestinal bacteria in the gastrointestinal tract.

18 hepatic metabolites were predicted for the test substance, respectively. The metabolites are mainly the result of hydrolysis of the ester bonds and of a hydroxyl group being added. In general, the hydroxyl groups make the substances more water-soluble and susceptible to metabolism by phase II-enzymes. The smaller molecules resulting from hydrolysis of the ester bond are also expected to have higher water solubility. Up to 37 metabolites were predicted to result from all kinds of microbiological metabolism for the test substance. Most of the metabolites were found to be a consequence of the degradation of the molecule. Not all of these reactions are expected to take place in the human GI-tract. The hydrolysis products may be conjugated (e.g. glucuronidation) to form a polar molecule suitable for excretion or metabolism.

Available genotoxicity data of the test substance might indicate clastogenic properties. In particular, a positive result was observed in an in vitro chromosome aberration test in Chinese hamster lung fibroblasts following metabolic activation with microsomal S9 mix. However, the same test performed without metabolic activation was negative. The test substance did not exhibit mutagenic properties in an Ames test with and without metabolic activation. Therefore, results on genotoxicity are equivocal and clastogenicity of the test substance following metabolic activation cannot be excluded. In vivo genotoxicity testing is planned to receive detailed information on the genotoxic potential of 2-(butylcarbamoyloxy)ethyl prop-2-enoate.

Excretion

The hydrolysis products of 2-(butylcarbamoyloxy)ethyl prop-2-enoate will be conjugated with e.g. glutathione to form more water-soluble molecules and excreted via the urine or metabolised.

The fraction of the target substance that is not absorbed in the GI tract will be excreted via the faeces. If microbial metabolism occurs (as predicted in the OECD QSAR Toolbox, see above under ‘Metabolism’), then the smaller metabolites may be absorbed; thereby entering the systemic circulation. The metabolites are expected to be conjugated as described above and excreted via the urine. The formation of CO2 as metabolite is also predicted. This metabolite will be excreted via the exhaled air.

 

References

ECHA (2017). Guidance on information requirements and chemical safety assessment, Chapter R.7c: Endpoint specific guidance. Version 3.0.

Mostert, V., Goergens, A., 2011. Dermal DNEL setting: using QSAR predictions for dermal absorption for a refined route-to-route extrapolation. Toxicologist 120, 107

 

OECD (2014). (Q)SAR Toolbox v3.3. Developed by Laboratory of Mathematical Chemistry, Bulgaria for the Organisation for Economic Co-operation and Development (OECD). Prediction performed 21 June 2016.http://toolbox.oasis-lmc.org/?section=overview

US EPA (2014). Estimation Programs Interface Suite™ for Microsoft® Windows, v 4.11. United States Environmental Protection Agency, Washington, DC, USA. Downloaded from: http://www.epa.gov/oppt/exposure/pubs/episuite.htm