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In this assessment, absorption and distribution of 3G8 (CAS n° 94-28-0) will be successively reviewed based on physicochemical properties and available data of the compound components after potential hydrolysis.

The absorption of 3G8 is anticipated to be low based upon physicochemical characteristics, both after dermal, oral and respiratory application (see separate assessments below). The water solubility is low, whereas the fat solubility, represented by the Log Pow is estimated to be high. The absorption may increase in function of the concentration. Once in the body, the substance (3G8) may be distributed quite widely through the organs, as demonstrated by the variety of target organs in the OECD 422 study (Van Tuyl, 2010), however only at a high dose level of 15000 ppm in the diet, corresponding to 977-1563 mg/kg bw/day (at the borderline of the limit dose). In the same study, liver weight increases and histopathological hepatocellular hypertrophy at the high dose level may also indicate adaptive effects, including enzyme induction and biotransformation of the products in the liver.

 

On the other hand, 3G8 is expected to undergo hydrolysis in the aqueous environment of the gastrointestinal tract.The expected hydrolysis products are 2-ethyl hexanoic acid (2-EHA) and triethylene glycol (TG). Literature is available for these two substances, however it is not know to what extent hydrolysis takes place in humans and animals at the biological barriers (epidermis, gastrointestinal mucosa and lung alveolus) or internal organs. Therefore the assessment below is purely theoretical, and may therefore not be fully representative for 38G as long as this has not been measured.

 

Based on several studies it has been concluded that 2 -EHA (one of the potential hydrolysis products) is relatively well absorbed via oral and dermal exposure. Most of the percentage of the dose applied is excreted in the urine. After oral gavage dosing at 100 and 1000 mg/kg in rats, approximately 72 to 75 % of the dose was excreted in the urine within 24 hr; fecal excretion accounted for 7 to 12 %. After dermal application of 100 and 1000 mg/kg in rats, approximately 30 % of the applied dose was excreted in the urine during the first 24 hr.; fecal excretion was 7 % for both dose levels. After dermal application, peak blood levels of 14C occurred about 5.7 hr after application and the absorption half-life was 3.2 hr. After intravenous injection in rats, the highest concentrations were observed in the liver, the kidney and the blood. It was also concluded that the concentration of 2-EHA rapidly declined and was hardly measurable at 24h after administration. The results suggest that 2-EHA is rapidly cleared from the tissues.


Triethylene glycol is also relatively well absorbed via oral exposure and again, most of the percentage of the dose applied is excreted mainly in the urine. The radioactivity recovered amounted to 0.8 to 1.2% in expired air, 2.0 to 5.3% in feces, and 86.1 to 94.0% in urine. On the other hand, exposure of Triethylene glycol via dermal application seems to be irrelevant.

A. ASSESSMENT OF ABSORPTION

 

1. Dermal exposure

 

Table 1: Information on the potential of the substance to be absorbed or taken up following dermal exposure.

Data source

Results

Remarks

Molecular Formula

C22H42O6

 

Physical form

Clear colourless liquid

Liquids and substances in solution are taken up more readily than dry particulates. 

Molecular weight

402.56528 [g/mol]

< 100: favorable for dermal uptake.

> 500: may be too large

Water solubility

1.5-2 mg/L

The substance must be sufficiently soluble in water to partition from the stratum corneum into the epidermis. Between 1-100 mg/L, the absorption is anticipated to be low to moderate.

Log Pow

6.10

 

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.

Vapor pressure

1 * 10-5 hPa

Vapors of substances with vapor pressure below 100 Pa (0.76 mmHg at 25°C) are likely to be well absorbed and the amount absorbed dermally may be more than 10% of the amount that would be absorbed by inhalation.

Skin irritation / corrosivity

Not irritant

No skin damage so will not enhance the penetration.

Dermal toxicity data

LD50 > 2000 mg/kg

There were no deaths, no signs of systemic toxicity, no signs of dermal irritation, no unexpected gains in body weight and no abnormalities at necropsy.

Skin sensitization data

Not a sensitizer. There were no deaths, no signs of systemic toxicity and no unexpected gains in body weight.

No skin damage so will not enhance the penetration.

 

Based on its molecular weight, the 3G8 molecule is able to pass through the skin but is not small enough to be readily absorbed dermally.

 

The water solubility and the Log Pow also indicate a low absorption. Highly lipophilic substances (Log Pow between 4 and 6) that come into contact with the skin can readily penetrate the lipid rich stratum corneum but are not well absorbed systemically. Although they may persist in the stratum corneum, they will eventually be cleared as the stratum corneum is sloughed off. A turnover time of 12 days has been quoted for skin epithelial cells (TGD).

 

The lack of irritation and systemic effects after dermal exposure in experimental data is additional information stressing the fact that the penetration may be really low. Finally it is important to note that absence of clear systemic toxicity after dermal exposure does not demonstrate a lack of absorption, but it may indicate that 3G8 is of low toxicity.

 

2. Oral exposure

 

Table 2:Information on the potential of the substance to be absorbed from the gastrointestinal tract.

Data source

Results

Remarks

Molecular Formula

C22H42O6

Substance is not ionisable.

Molecular weight

402.56528 [g/mol]

Molecular weight < 500 is favorable for absorption via the GI tract.

Water solubility

1.5-2 mg/l

Absorption is anticipated to be low by passive diffusion and as the molecular weight is above 200, the substance may not pass through aqueous pores or be carried through the epithelial barrier by the bulk passage of water.

Log Pow

6.10

Log Pow > 4 is not favorable for absorption by passive diffusion but the substance may be taken up by micellular solubilisation.

Oral toxicity data

LD50 > 2000 mg/kg

There were no deaths, no signs of systemic toxicity, no unexpected gains in body weight and no abnormalities at necropsy

Hydrolysis test

Expected hydrolysis products are “mono-ester”, 2-ethyl hexanoic acid and triethylene glycol.

If a substance undergoes hydrolysis in the GI tract, the bioavailability of the parent compound will be reduced and toxicokinetic predictions based on the characteristics of the parent compound may be less relevant. (currently no test results available)

 

The physicochemical properties of 3G8 mentioned above are not in favor of absorption by passive diffusion from the gastrointestinal tract. This is supported by experimental data, which did not indicate systemic effects after acute oral exposure. Absence of clear systemic toxicity after exposure does not demonstrate a lack of absorption, but it may indicate that the toxicity of 3G8 is low.

 

As 3G8 does not contain any ionisable groups, its absorption is not influenced by the pH of the gastrointestinal tract (pH2). On the other hand, 3G8 may be hydrolyzed. One of the expected hydrolysis products is 2-ethyl hexanoic acid (2EHA). The pKa of 2EHA is equal to 4.8. Since the absorption of acids is favored at pHs below their pKa, it is suggested that 2EHA would preferentially absorbed in the stomach.

 


3. Exposure via inhalation

 

Table 3:Information on the potential of the substance to be absorbed from the respiratory tract.

Data source

Results

Remarks

Vapor pressure

1 * 10-5 hPa

The substance has a low volatility and therefore will not be easily available as a vapor and therefore exposure is not expected.

Particle size

MMAD of the aerosol was 2.0 μm (Dupont, 2005)

The atmosphere of 3G8 was considered to be respirable in rats. The particles have the greatest probability of settling in the nasopharyngeal region.

Log Pow

6.10

 

A moderate Log Pow (between 0 – 4) would be favourable for absorption directly across the respiratory tract epithelium.

Water solubility

1.5-2 mg/l

Absorption is anticipated to be low by passive diffusion and as the molecular weight is above 200, the substance may not pass through aqueous pores.

Inhalation toxicity data

ALC and LC50>2000 mg/m³;

No deaths, no notable clinical signs of toxicity or changes in body weight.

Oral toxicity data

LD50 > 2000 mg/kg; There were no deaths, no signs of systemic toxicity, no unexpected gains in bw and no abnormalities at necropsy.

No sign of systemic toxicity is not a proof that absorption has not occurred.

 

The type of inhalation exposure to 3G8 will vary dependent on the form of the substance,  namely a gas/vapor or a liquid aerosol.

  • Gas/vapor: 3G8 has a low vapor pressure and consequently a low volatility. 3G8 will be poorly available for inhalation as a vapor.
  • Liquid aerosol: The potential for liquid aerosols to be inhaled will be determined by their particle size. The ability of a liquid to form an aerosol and the characteristics of that aerosol will depend on the way the liquid is being used and the process that generated the aerosol. The data from DuPont (2005) reported that the atmosphere of 3G8 was considered respirable. The aerodynamic diameters of the particles of 2.0 µm suggest that the particles have the greatest probability of settling in the nasopharyngeal region.

Nevertheless, for 3G8 this exposure scenario appears to be highly unlikely.

 

Results from water solubility and Log Pow indicate that absorption by passive diffusion -once the substance will be in contact with the respiratory tract epithelium - will be low. In addition, due to the low solubility of the substance, the probability to be retained in the mucus and transported out of the respiratory tract with the mucus is low.

 

As a consequence, although an exposure of 3G8 via inhalation seems to be highly unlikely to irrelevant (both for gases/vapors and liquid aerosols), a high concentration of 3G8 in the respiratory tract may lead to an absorption of the substance through the respiratory tract epithelium due to an accumulation of the substance in the lung.

 

B. ASSESSMENT OF DISTRIBUTION

 

Table 4:Relevant information for the evaluation of the distribution of the substance (parent compound).

 

Data source

Results

Remarks

Molecular weight

402.56528 [g/mol]

The smaller the molecule, the wider the distribution.

Water solubility

1.5-2 mg/l

The distribution may vary by the rate at which molecules diffuse across membranes.

Log Pow

6.10

Likely to distribute into cells and the intracellular concentration may be higher than extracellular concentration particularly in fatty tissues.

Target organs

OECD 422 study (Van Tuyl, 2010);

At 15000 ppm in the diet (977-1563 mg/kg bw/day), parental toxicity consisted of decreased motor activity for females, decreased bw gain for males and females, haematological changes for females, changes in clinical biochemistry parameters, organ weight changes (increased liver and kidney weights for both sexes, decreased thymus weight for females) and histopathological findings.

Microscopic findings related to treatment were recorded in the adrenal glands, kidneys, liver, pituitary gland, spleen, thymus and thyroid glands for males and females.

 

Once the substance is absorbed (via dermal, oral or inhalation route), due to its low water solubility, the distribution into the body is likely to be high. But this may be limited in to a certain extent by the fact that the molecular weight of 3G8 is relatively large and its Log Pow is relatively high.

 

Lipophilic substances have the potential to accumulate within the body if the dosing interval is shorter than 4 times the whole body half-life. Substances with high log Pow values (log Pow > 4) tend to have longer half-life. On this basis, there is the potential for such substances to accumulate in individuals that are frequently exposed to that substance (TGD).

 

The large distribution of 3G8 in the body after repeated exposure of a high concentration is supported by experimental data (OECD 422 study, 2010). At lower exposure levels (1000 and 5000 ppm), no effects were observed. The NOAEL of 5000 ppm corresponded with 314-576 mg/kg bw/day.

 

C. ASSESSMENT OF METABOLISM

 

In the OECD 422 study (Van Tuyl, 2010), liver changes were observed as demonstrated by organ weight changes (increased liver weigths for both sexes) and histopathological findings (diffuse midzonal /centrilobular hypertrophy). Relative liver weight increases at the 15000 ppm group versus control group approximated 23% in male rats and 30% in female groups. Liver effects such as liver weight increase and histopathological hepatocellular hypertrophy in experimental animals have been described in literature as frequently observed and adaptive effects, often related to enzyme induction and biotransformation of the products in the liver. Liver enlargement associated with an increase in the activity of xenobiotic metabolising enzymes is an adaptation to increased functional load, and is therefore considered to be a physiological rather than a pathological response or adverse effect (Andrew, 2005).

 

D. ASSESSMENT OF EXCRETION

 

No data available for 38G, however data are available for the potential hydrolysis products.

 

1) 2-ethylhexanoic acid; CASn° 149-57-5

Classification: Repr. Cat. 3; R63

Risk phrases:R63: Possible risk of harm to the unborn child. 

2-EHA is an isomer of the antiepileptic drug, valproic acid. Valproic acid causes hyperaminonaemia as a harmful side effect (Gal et a1.1988; Marini et al.1988). In the rat liver mitochondria 2-EHA was observed to inhibit the urea cycle (Manninen et al.1989). 

  • Absorption, Distribution & Excretion after oral gavage: [2-14(C)-Hexyl]2-ethylhexanoic acid in corn oil was administered to female rats as a single oral gavage at 100 or 1000 mg/kg. Approximately 72 to 75 % of the oral dose was excreted in the urine within 24 hr, and <10 % was excreted after 24 hr. About 50% of the 14(C) was excreted in the first 8 hr after the 100-mg/kg dose versus 20 % after the 1000 mg/kg dose. Fecal excretion accounted for 7 to 12 % of both doses (Bingham et al., 2001).
  • Absorption, Distribution & Excretion after dermal exposure: An aqueous solution of [2-14(C)-hexyl]2-ethylhexanoic acid was applied topically at either 100 or 1000 mg/kg. After dermal application, approximately 30 % of the applied dose was excreted in the urine during the first 24 hr, followed by an additional 8 and 17 % from 24 to 96 hr for the 100- and 1000-mg/kg doses, respectively. Fecal excretion was 7 % for both dose levels. After dermal application, peak blood levels of 14C occurred about 5.7 hr after application and the absorption half-life was 3.2 hr (Bingham et al., 2001).
  • Absorption, Distribution & Excretion after intravenous injection: Rats received 2-ethylhexanoic acid by intravenous injection (1 mg/kg). After intravenous injection, 64 % of the l4(C) was excreted in the urine and 2 % in the feces (Bingham et al., 2001). Other groups of rats and mice received single intraperitoneal dose of 2-(14)C-ethylhexanoic acid (2-(14)C-EHA). After 30 min, 2 and 6 hr of exposure, animals were sacrificed. In mice, the highest uptake of 2-(14)C-EHA was observed in the liver, kidney and blood. In contrast, low uptake of 2-(14)C-EHA was seen in the brain. 2-(14)C-EHA was well detectable in the olfactory bulb and in the salivary gland.In rats,at 2 hr after administration the highest concentration of 2-(14)C-EHA occurred in blood. The radioactivity in the liver and kidney was also relatively high. The concentrations of 2-(14)C-EHA were low in the brain. By 6 hr, the radioactivity had decreased rapidly and was hardly measurable at 24 hr after the administration. The results suggest that 2-ethylhexanoic acid is rapidly cleared from the tissues (Pennanen et al., 1991).
  • Metabolism: Major urinary metabolites included the glucuronide of 2-ethylhexanoic acid, the glucuronides of 2-ethyl-6-hydroxyhexanoic acid and 2-ethyl-1,6-hexanedioic acid, and unmetabolised 2-ethylhexanoic acid. The proportions of each metabolite changed with the dose and route of administration (Bingham et al., 2001).
  • Biological Half-Life: In female rats, blood levels after intravenous injection appear to decay in a triphasic manner with half-lives of 0.19+0.11 hrs, 6.6+3.9 hrs, and 117+47 hrs. After oral administration, peak blood levels were achieved after 15 or 30 minutes, and also declined triphasically with half-lives similar to what had been estimated from intravenous administration (0.32+0.04 hrs, 6.8+3.5 hrs, and 98.2+32.8 hrs). Dermal application resulted in slower absorption with peak blood levels occurring 5.7+0.4 hours after application and a half-life of 3.2+0.1 hr. Elimination was biphasic with half-lives of 4.2+0.2 and 251+135 hrs (EPA, 2002).

2) Triethylene glycol; CAS n° 112-27-6

This substance is not classified in the Annex I of Directive 67/548/as such.

 

Triethylene Glycol is a fragrance ingredient and viscosity decreasing agent in cosmetic formulations. With oral LD50 values in rodents from 15 to 22 g/kg, this compound has little acute toxicity.

 

  • Absorption, Distribution & Excretion after oral administration: Male rats were given a single oral dose of 22.5 mg randomly radiolabelled 14-C-triethylene glycol. Urine, feces, and expired air were collected over a period of 5 days. The radioactivity recovered (in % of the administered dose) amounted to 0.8 to 1.2% in expired air, 2.0 to 5.3% in feces, and 86.1 to 94.0% in urine. The total recovery of radioactivity was 90.6% to 98.3% of the administered dose (McKennis et al. 1962).

    Following oral exposure, rabbits dosed with 200 or 2000 mg/kg triethylene glycol respectively excreted 34.3% or 28%, of the administered dose in the urine as unchanged triethylene glycol and 35.2% as a hydroxyacid form of this chemical (McKennis et al. 1962).

 

  • Absorption, Distribution & Excretion after dermal exposure: No studies have been reported dealing with the skin absorption of triethylene glycol.Although it is possible that under conditions of very severe prolonged exposures to this chemical, absorption through the skin can occur, it is doubtful any appreciable systemic/dermal injury would occur because triethylene glycol has (1) a low order of dermal irritancy, (2) is not a dermal sensitizer, and (3) showed no evidence of dermal or systemic toxicity following repeated dermal applications of 2 mL (approximately 600 mg/kg) triethylene glycol applied to the skin of rabbits in a 21-day dermal toxicity study (EPA, 2003).


POTENTIAL HYDROLYSIS PRODUCTS: CONCLUSIONS

 

2-ethylhexanoic acid is relatively well absorbed via oral and dermal exposure. Most of the percentage of the dose applied is excreted in the urine. After intravenous injection, three target organs were observed: the liver, the kidney and the blood. It was also concluded that 2-ethylhexanoic acid is rapidly cleared from the tissues.


Triethylene glycol is also relatively well absorbed via oral exposure and again, most of the percentage of the dose applied is excreted in the urine. On the other hand, exposure of Triethylene glycol via dermal application seems to be irrelevant.

References related to these toxicokinetic endpoints

 

Andrew D. (2005)PSDGuidance Document:Interpretation of Liver Enlargement in Regulatory Toxicity Studies.

Bingham E., Cohrssen B., Powell C.H. (2001) Patty's Toxicology Volumes 1-9 5th ed. John Wiley & Sons.New York,N.Y.: p. 5:730

EPA (2002) Robust Summaries & Test Plans: Metal Carboxylates; Revised Summaries, Appendix 1.0. Robust Summaries and SIDS Dossier for 2-Ethvlhexanoic acid. Available from, as ofJuly 31, 2007: http://www.epa.gov/HPV/pubs/summaries/metalcarb/c14172rr1.pdf

Gal P., Oles ., K. S., Gilman J. T. and Weaver R. (1988) Valproic acid efficacy, toxicity, and pharmacokinetics in neonates with intractable seizures. Neurology 38, 467-471.

Manninen A., Kröger S., Liesivuori J. and Savolainen H. (1989) 2-Ethylhexanoic acid inhibits urea synthesis and stimulates carnitine acetyltransferase activity in rat liver mitochondria. Arch. Toxicol.: 63, 160-161.

McKennis, Jr., Turner H., R. A., Turnbull L. B., Bowman E. R., Muelder W.W., Neidhardt M. P., Hake C. L., Henderson R., Nadaeu H. G., and Spencer S. (1962) The excretion and metabolism of triethylene glycol. Toxicol. Appl. Pharmacol.: 4:411–431.

Pennanen S. and Manninen A. (1991) Distribution of 2-Ethylhexanoic acid in mice and rats after
an intraperitoneal injection. Pharmacology & Toxicology: 68, 57-59.

Marini, A. M., Zaret B. S. and Beckner R. (1988) Hepatic and renal contributions to valproic acid-induced hyperammonemia. Neurology: 38, 365-371.