Tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics, other

Remarks:

Expert statement

Type of information:

other: assessement of toxicokinetic behaviour based on physico-chemical properties and toxicological data

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: An assessment of the toxicokinetic behaviour of the pyromellitate target substance was performed, taking into account the chemical structure, the available physico-chemical-data and the available toxicological data.

Objective of study:

absorption

distribution

excretion

metabolism

toxicokinetics

Qualifier:

according to guideline

Guideline:

other: Technical guidance document, Part I, 2003; ECHA guidance R7C., 2014

GLP compliance:

no

Remarks:

Expert statement

Type:

absorption

Results:

The substance is only partially hydrolysed in the gastro-intestinal tract. Hydrolytic evidence indicated that only 2-ethylhexanol and a single isomer of mono-(2-ethylhexyl) trimellitate was absorbed.

Type:

distribution

Results:

Major organ of distrinution was the liver, followed by the lung and spleen. Small amounts were were found in heart, kidney, pancreas and adrenals.

Type:

metabolism

Results:

Following absorption, 2-ethylhexanol was extensively oxidatively metabolized and excreted. There was no evidence for the phase I metabolism of the partial esters of trimellitic acid.

Type:

excretion

Results:

High elimination rate in the faeces (76% within 144 hours) after oral administration of the substance, faecal elimination was found to be markedly lower after intravenous application. 16.3% was found in urine, 1.9% in expired air.

Details on absorption:

In an OECD 417 study two peaks in the rate plot of 14 CO2 excretion in expired air were observed for each rat following oral exposure. The first was observed 2-3 hours post dose and the second 8-12 hours post dose. The authors suggested that the biphasic excretion was resulting from the release of radiolabeled 2-ethylhexanol by hydrolysis from the tri-ester followed by a further hydrolysis step releasing 2-ethylhexanol from the di-ester. The half-life for initial absorption was estimated to be approximately 0.7 hours.

The in vitro dermal absorption of tris(2-ethylhexyl) trimellitate was measured using full-thickness skin samples, which had been excised from female nude mice and specific pathogen-free pigs, in a Franz diffusion cell system (Pan et al., 2014; see also review by Fiume MM and Heldreth, 2015). The receptor medium contained 40% ethanol, and the donor medium a buffer with 40% ethanol and 5.4 mM tris(2-ethylhexyl) trimellitate (pH 7.4). The skin samples were removed from the Franz cells after a 12-hour exposure and then tape-stripped. The accumulation of tris(2-ethylhexyl) trimellitate was 1.32 ± 0.53 nmol/mg in nude mouse and 0.35 ± 0.19 nmol/mg in pig skin; the flux was 0 nmol/cm2/h for both mouse and pig skin. Tris(2-ethylhexyl) trimellitate was not found in the receptor medium after 12 hours. It was concluded that the test did not indicate any systemic bioavailability after dermal exposure to tris(2-ethylhexyl) trimellitate.

Available toxicokinetic data may imply that the extend of monoester formation in the gastrointestinal tract, as well as the absorption and systemic bioavailability decreases with an increasing number of ester bonds (2 ester bonds occur in phthalates, 3 in the source substance, 4 in the target substance). Therefore, it seems to be plausible that the gastrointestinal absorption of hydrolysis products of the target substance, i.e. the potential metabolites 2-ethylhexan-1-ol and mono-(2-ethylhexyl) pyromellitate, is very low.

Details on distribution in tissues:

In the OECD 417 study residual radioactivity in the carcass 144 hours post dose was <0.6% of the administered dose. Tissues analysed for radioactivity revealed only liver (5x) and adipose tissue (3x) containing levels of radioactivity greater than the carcass average. These findings suggested a low bioaccumulation potential of tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate (other name: tris-(2-ethylhexyl) trimellitate).

In another srudy twenty-eight rats were dosed intravenously with 15.6 mg/kg [14C-carbonyl] tris(2-ethylhexyl) trimellitate (28.0 μCi/kg) in 2.6-3.6 ml of the vehicle; groups of 4 rats were killed at 1, 6, 24, 48, 72, 168, and 336 h after dosing. Blood samples, urine, and feces were collected, and at necropsy, several organs were removed and analyzed for radioactivity. The liver was the major organ of uptake (peak radioactivity 71.6% after 24 hours, declining to 44.8% after 14 days). The lungs accounted for 18.6% of the administered dose after 1 hour. The percent dose in the lungs declined to 0.6% after 7 days. The levels in the spleen remained constant throughout the 14-day period (5.3% at 24 h). Small amounts of radioactivity were found in the heart, kidney, pancreas and adrenals. After 7 days, the dose levels in the latter organs accounted for less than 0.1% of the radioactivity.

Details on excretion:

The excretion of radioactivity following administration of a single oral dose in an OECD 417 study occurred mainly in the faeces, this accounting for approximately 75% of the administered dose with 16.3% found in the urine and 1.9% in expired air. Radioactivity in the faecal extracts was identified as 86% native substance, 7% di-(2-ethylhexyl) trimellitate and 1% mono-(2-ethylhexyl) trimellitate. Only one out of three possible mono-ester isomers was found. Analysis of urine by GC/MS revealed the presence of 2-ethylhexanol, 2-ethylhexanoic acid, 2-heptanone and mono-(2-ethylhexyl) trimellitate. HPLC retention times indicated that the mono-ester was the same isomer found in faecal extracts. No isomers of di-(2-ethylhexyl) trimellitate were found in the urine. Thus, the di-ester appeared to be poorly absorbed. Urinary elimination of radioactivity was bi-phasic with half-lives of 3.1 and 42 hours.

In contrast to the high elimination rate in the faeces (76% within 144 hours) after oral administration of the substance, faecal elimination was found to be markedly lower after intravenous application to male Sprague-Dawley rats. Serial blood sampling was conducted with 5 rats dosed intravenously with 10.5 mg/kg [14C-carbonyl] tris(2-ethylhexyl) trimellitate (>98% radiochemically pure; 59.9 μCi/kg) in 2.5-3.5 ml of a soybean oil-water (10:90) emulsion. Blood samples were collected prior to dosing and at 10 times points from 0.5 h to 336 h (14 days) after dosing. The animals were placed in metabolism cages, and urine and fecal samples were collected at various intervals 14 days. The distribution half-life, disposition half-life, apparent distribution volume, and plasma clearance were 46.2 min, 5.34 days, 7.49 l/kg, and 40.5 ml/kg·h, respectively, indicating a fairly rapid initial distribution and slow clearance of triethylhexyl trimellitate from the body. Over the 14-day period, 3.3% of the radioactivity was recovered in the urine and 16.9% was recovered in the feces; renal clearance was 13 ml/kg·h.

Metabolites identified:

yes

Details on metabolites:

The substance is only partially hydrolysed in the gastro-intestinal tract to 2-ethylhexanol and the corresponding di-ester and, following further hydrolysis, the mono-ester. Hydrolytic evidence indicated that only 2-ethylhexanol and a single isomer of mono-(2-ethylhexyl) trimellitate was absorbed. Following absorption, 2-ethylhexanol was extensively oxidatively metabolized and excreted. There was no evidence for the phase I metabolism of the partial esters of trimellitic acid in contrast with findings for phthalates such as DEHP. Due to differences in absorption and metabolism, it is unlikely that the compound will produce the same toxic effects that were reported for DEHP.

Prediction of metabolites by the hydrolysis simulator (acidic) and hydrolysis simulator (basic) resulted in an identical set of 7 metabolites in each case for tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate, and a set of 8 metabolites for tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate. Obviously, the prediction is based on the assumption that the ester bonds of trimellitic acid and pyromellitic acid, respectively, are successively hydrolysed, with the result that all of the possible isomers are released. An overview of predicted hydrolysis products and compounds yielded by the metabolism simulators is presented in Table 1, along with experimental data.

Table 1: Overview of metabolites including hydrolysis products

Chemical	Target substance	Source substance
EC name, EC No, CAS No	Tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate, EC No 221-508-0, CAS No 3126-80-5	Tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate, EC No 222-020-0, CAS No 3319-31-1
	Presumed metabolites based on experimental data of the source	Analysis data from toxicokinetics study acc. to OECD TG 419 (one dose level only)
Compounds in urine	2-Ethylhexan-1-ol, 2-ethylhexanoic acid, 2-heptanone, mono-(2-ethylhexyl) pyromellitate	2-Ethylhexan-1-ol, 2-ethylhexanoic acid, 2-heptanone, mono-(2-ethylhexyl) trimellitate (only 1 out of 3 possible isomers)
Compounds in faeces	Tetra(2-ethylhexyl) pyromellitate, tris(2-ethylhexyl) pyromellitate, di-(2-ethylhexyl) pyromellitate, mono-(2-ethylhexyl) pyromellitate	Tris(2-ethylhexyl) trimellitate (86%), di-(2-ethylhexyl) trimellitate (7%), mono-(2-ethylhexyl) trimellitate (1% - only 1 out of 3 possible isomers)
Probably absorbed compounds	2-Ethylhexan-1-ol, mono-(2-ethylhexyl) pyromellitate	2-Ethylhexan-1-ol, mono-(2-ethylhexyl) trimellitate (only 1 out of 3 possible isomers)
	Compounds predicted by OECD Toolbox (v. 4.1)
Hydrolysis simulator (acidic/basic)	7 metabolites: 2-ethylhexan-1-ol, tris(2-ethylhexyl) pyromellitate, di-(2-ethylhexyl) pyromellitate (3 isomers), mono-(2-ethylhexyl) pyromellitate (1 isomer), pyromellitic acid	8 metabolites: 2-ethylhexan-1-ol, di-(2-ethylhexyl) trimellitate (3 isomers), mono-(2-ethylhexyl) trimellitate (3 isomers), trimellitic acid
In vivo rat liver metabolism simulator	7 metabolites: 2-ethylhexanoic acid, 2-ethylhexanal, 2-ethylhexan-1-ol, tris(2-ethylhexyl) pyromellitate, di-(2-ethylhexyl) pyromellitate (3 isomers)
Rat liver S9 metabolism simulator	7 metabolites: 2-ethylhexanoic acid, 2-ethylhexanal, 2-ethylhexan-1-ol, tris(2-ethylhexyl) pyromellitate, di-(2-ethylhexyl) pyromellitate (3 isomers)	10 metabolites: 2-ethylhexanoic acid, 2-ethylhexanal, 2-ethylhexan-1-ol, di-(2-ethylhexyl) trimellitate (3 isomers), mono-(2-ethylhexyl) trimellitate (3 isomers), trimellitic acid
Skin metabolism simulator	2 metabolites: 2-ethyl hexan-1-ol, tris(2-ethylhexyl) pyromellitate	4 metabolites: 2-ethylhexan-1-ol, di-(2-ethylhexyl) trimellitate (3 isomers)
Tautomerism	1 metabolite	1 metabolite
Microbial metabolism simulator	94 metabolites	166 metabolites

Justification of the read-across hypothesis in terms of human health effects

Structural similarity

 

Functional groups and substituents

The chemical structures of the target and the source substances can be described as esters of 2-ethylhexanol with pyromellitic acid and trimellitic acid, respectively. Four or three formic acid residues which show an ester bond with branched alkane substituents are attached to an aromatic ring (benzol), respectively. The organic functional groups are specified in Table 2 which shows that the target and the source chemical are characterized by the same type of organic functional groups. Only the number of ‘carboxylic acid esters’ with ‘alkanes, branched with tertiary carbon’ is varying (4 vs 3, respectively). The sub-structure feature, which is shared by phthalates as well as the source and target compound, is phthalic acid, synonym 1,2-benzenedicarboxylic acid. The conformation, i.e. spatial arrangement of atoms in the molecules of the target and the source substance, is flexible.

Table 2: Comparison of chemical structures, functional groups and substituents, under consideration of profiling results (OECD Toolbox v. 4.1)

Chemical	Target substance	Source substance
EC name, EC No, CAS No	Tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate, EC No 221-508-0, CAS No 3126-80-5	Tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate, EC No 222-020-0, CAS No 3319-31-1
Chemical structure
Description of basic structure	Esters of 2-ethylhexanol with pyromellitic acid	Esters of 2-ethylhexanol with trimellitatic acid
Key substituents	Branched alkyl	Branched alkyl
Organic functional groups (nested)	Alkane, branched with tertiary carbon (4) Aryl Carboxylic acid ester (4) Overlapped groups	Alkane, branched with tertiary carbon (3) Aryl Carboxylic acid ester (3) Overlapped groups
Organic functional groups (US EPA)	Aliphatic carbon [CH] Aliphatic carbon [-CH2-] Aliphatic carbon [-CH3] Aromatic carbon [C] Carbonyl, one aromatic attach [-C(=O)-] Ester, aliphatic attach [-C(=O)O] Miscellaneous sulfide (=S) or oxide (=O) Olefinic carbon [=CH- or =CH<] Tertiary carbon	Aliphatic carbon [CH] Aliphatic carbon [-CH2-] Aliphatic carbon [-CH3] Aromatic carbon [C] Carbonyl, one aromatic attach [-C(=O)-] Ester, aliphatic attach [-C(=O)O] Miscellaneous sulfide (=S) or oxide (=O) Olefinic carbon [=CH- or =CH<] Tertiary carbon
Organic functional groups, Norbert Haider (checkmol)	Aromatic compound Carboxylic acid derivative Carboxylic acid ester	Aromatic compound Carboxylic acid derivative Carboxylic acid ester
Tautomers	Stable form	Stable form

In case of the supporting substance, the substituents are linear, straight-chain alkanes.

PubChem substructure similarity features

The structural similarity of the target and source read-across substances has in addition been verified by application of PubChem substructure similarity features which are implemented in OECD Toolbox (v. 4.1).

 

Method: The PubChem generates a substructure fingerprint for each chemical structure. These fingerprints are used for similarity neighboring. In this context, a substructure is a fragment of chemical structure. A fingerprint is an ordered list of binary (1/0) bits. Each bit represents a Boolean determination of specific atom or test features. 7 groups of PubChem features have been defined:

·        Hierarchical element counts;

·        Rings;

·        Simple atom pairs;

·        Simple atom nearest neighbors;

·        Detailed atom neighbors;

·        Simple SMARTS patterns (SMART is a language that allows specifying substructures by using rules that are straightforward extensions of SMILES);

·        Complex SMARTS patterns.

 

Results: The target compound shares 111 out of 112 substructure features with the source whereas the source compound shares 111 out of 113 substructure features with the target substance.

Similarities in compounds including metabolites the organism is exposed to

The assessment of similarities in compounds the organism is exposed to relies on experimental data regarding the toxicokinetics of tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate as well as the prediction of hydrolysis products and metabolites by OECD Toolbox (v. 4.1) both for the source and target read-across substance. Hydrolysis of ester bonds by intestinal and liver esterases is also well established (Younggil, 2001). Moreover, substantial information on in vivo metabolism of phthalates such as mono(2-ethylhexyl) phthalate (MEHP, CAS No 4376-20-9, EC No 224-477-1) is considered since differences in metabolism can endorse the view that tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate and tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate are less toxic than low molecular weight phthalates

Discussion of the experimental results in comparison to toxicokinetic characteristics of phthalates

In contrast to the low oral absorption noted after administration of the source substance the extent of absorption of the phthalate DEHP was around 50% for doses up to about 200 mg/kg bw in rats, non-human primates and humans, probably in the form of the mono-ester (European Chemicals Bureau, 2008). Only at higher doses, it appears that absorption in non-human primates is dose-limited in contrast to rodents. Unlike the mono-ester produced by hydrolysis of the source substance, the mono-ester of the phthalate (MEHP) is further intensively metabolised in the liver by oxidation. As a consequence, some 20 metabolites have been identified in the urine of rats.

Table 3: Studies on absorption, metabolism, distribution and elimination

Method	Results	Remarks	Reference
rat (Sprague-Dawley) male oral: gavage Exposure regime: Dosed once only Doses/conc.: 100 mg/kg body weight (16-18 microCi/animal) equivalent or similar to OECD Guideline 417 (Toxicokinetics)	Main ADME results: absorption: Half-life - 0.7 hours excretion: Half-life - 42 hours Metabolites identified: yes Details on metabolites: Radioactivity in the faecal extracts was identified as 86% TOTM, 7% di-(2-ethylhexyl) trimellitate and 1% mono-(2-ethylhexyl) trimellitate. Only one out of three possible mono-ester isomers was found. Analysis of urine by GC/MS revealed the presence of 2-ethylhexanol, 2-ethylhexanoic acid, 2-heptanone and mono-(2-ethylhexyl) trimellitate. HPLC retention times indicated that the mono-ester was the same isomer found in faecal extracts. No isomers of di-(2-ethylhexyl) trimellitate were found. Evaluation of results: low bioaccumulation potential based on study results	1 (reliable without restriction) key study experimental result Test material (Common name): Tri-(2- ethylhexyl) trimellitate	Enriquez PM, Giordano CJ, DiVincenzo GD, 1984
rat (Sprague-Dawley) male intravenous Exposure regime: Single i.v. dose Doses/conc.: 10.5 mg/kg (59.9 uCi/kg) TOTM/TEHTM for blood sampling 15.6 mg/kg (28.0 uCi/kg) TOTM/TEHTM for tissue distribution & excretion To investigate the distribution & elimination kinetics of TOTM (TEHTM) following i.v. administration to rats	Main ADME results: distribution: See table below for the distribution of radioactivity in various tissues as a function of time. excretion: After 14d 16.9% of the administered dose was found in the faeces. See table below. excretion: After 14d 3.3% of the administered dose was found in the urine. See Table below. Metabolites identified: not measured Evaluation of results: low bioaccumulation potential based on study results	2 (reliable with restrictions) supporting study experimental result Test material (EC name): tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate	Martis L Freid E Woods E (1987)
in vitro study rat (Sprague-Dawley) male Not applicable Exposure regime: Not applicable Doses/conc.: Not applicable The rate of hydrolysis of a number of plasticisers has been examined using rat gut (small intestine) homogenates. Four plasticisers were examined, including tri((2-ethylhexyl) trimellitate. All were tested at concentrations to yield an equimolar concentration of 2-ethylhexanol. Homogenates were incubated with the substance for up to 30 minutes and samples taken at intervals during this time. Following inactivation of enzymes, solvent extraction was undertaken to provide samples for analysis.The kinetics of 2-ethylhexanol formation was examined.	Main ADME results: metabolism: No hydrolysis (metabolism) observed Evaluation of results: bioaccumulation potential cannot be judged based on study results	2 (reliable with restrictions) supporting study experimental result Test material (common name): tris(2-ethylhexyl) trimellitate	Fox JA, Enriques PM and DiVincenzo GD (1984)
In vitro dermal absorption study using full-thickness skin samples, which had been excised from female nude mice and specific pathogen-free pigs, in a Franz diffusion cell system	Accumulation 1.32 ± 0.53 nmol/mg in nude mouse and 0.35 ± 0.19 nmol/mg in pig skin; flux 0 nmol/cm2/h for both mouse and pig skin. The substance was not found in the receptor medium indicating no systemic bioavailability of the compound after dermal exposure.	2 (reliable with restrictions) key study Test material (common name): tris(2-ethylhexyl) trimellitate	Pan et al., 2014
IH SkinPerm model of dermal absorption (v. 2.0) as provided by the American Industrial Hygiene Association (AIHA): Calculation of the absorbed fraction as a result of dermal deposition at a rate of 1 mg/cm^2/h to 2000 cm^2skin area (hands and forearms) during 1 h	Absorbed fraction: 0.00165% Amount absorbed: 0.0331 mg Maximum dermal absorption: 1.03 x 10^-6mg/cm^2/h Dermal/respiratory uptake ratio (from airborne vapor): 0.86 Based on molecular weight 546.8 g/mol, vapour pressure 0.000000068 Pa at 25 °C (exp.), water solubility 0.00306 mg/L at 25 °C (exp.), octanol-water partition coefficient Log Po/w 8.0 (exp.), density 988.5 mg/cm^3(exp.), melting point -43 °C (exp.)	2 (reliable with restrictions) supporting study   Test material: tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate
IH SkinPerm model of dermal absorption (v. 2.0) as provided by the American Industrial Hygiene Association (AIHA): Calculation of the absorbed fraction as a result of dermal deposition at a rate of 1 mg/cm^2/h to 2000 cm^2skin area (hands and forearms) during 1 h	Absorbed fraction: 0.0000824% Amount absorbed: 0.00165 mg Maximum dermal absorption: 1.03 x 10^-6mg/cm^2/h Dermal/respiratory uptake ratio (from airborne vapor): 0.032 Based on molecular weight 702.5 g/mol, vapor pressure 0.00209 Pa (MPBPWIN™ by EPI Suite v.4.1), water solubility 1 mg/L (exp.), octanol-water partition coefficient Log Po/w 6.01 (exp.), density 0.9908 mg/cm^3(exp.), melting point -34 °C (exp.)	2 (reliable with restrictions) key study   Test material: tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate

Conclusions:

In conclusion, except for the hydrolysis product 2-ethylhexan-1-ol, the biotransformation products or metabolites of the source and target compound are similar as they show the same type but not the same number of functional groups. Available toxicokinetic data may imply that the extend of monoester formation in the gastrointestinal tract, as well as the absorption and systemic bioavailability decreases with an increasing number of ester bonds (2 ester bonds occur in phthalates, 3 in the source substance, 4 in the target substance). Therefore, it seems to be plausible that the gastrointestinal absorption of hydrolysis products of the target substance, i.e. the potential metabolites 2-ethylhexan-1-ol and mono-(2-ethylhexyl) pyromellitate, is very low. The latter metabolite will possibly not undergo a phase-I metabolism but rather be excreted unchanged in the urine, similarly to mono-(2-ethylhexyl) trimellitate. Especially due to low water solubility < 1 mg/L, the target substance is predicted by the IH SkinPerm model to be not absorbed through the skin. The low volatility of the target substance as well as the octanol-water partition coefficient (log Po/w of 6.01) will obviate a significant respiratory uptake.

Executive summary:

In order to assess the toxicokinetic behaviour of tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate the available physico-chemical and toxicological data for it and its near read across substances have been evaluated.

Hydrolysis by esterases is considered to be an important first step in the oral absorption of ortho-phthalates. The potential for such hydrolysis to occur with the source substance tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate has been examined in an in-vitro study using rat gut homogenate. There was no evidence of hydrolysis occurring wheras the corresponding phthalate, bis(2-ethylhexyl) phthalate (abbreviation DEHP, EC No 204-211-0, CAS No 117-81-7), was significantly hydrolysed.

The absorption, distribution, metabolism and elimination of the radiolabeled source substance have been investigated in the rat following oral administration of a single dose. Recovery of the administered dose was 94%, with approximately 75% eliminated unchanged in the faeces, 16.3% found in the urine and 1.9% in expired air. Residual radioactivity in the carcass after 6 days was <0.6% of the administered dose. Findings indicate that the compound may be partially hydrolysed in the gastro-intestinal tract to 2-ethylhexan-1-ol and the corresponding di-ester and, following further hydrolysis, the mono-ester. Only 2-ethylhexanol and a single isomer of the monoester (i.e. mono-(2-ethylhexyl) trimellitate) appear to be absorbed. Following absorption, 2-ethylhexanol was extensively metabolised with metabolites eliminated in the urine and as expired¹⁴CO₂. There was no evident metabolism of mono-(2-ethylhexyl) trimellitate, this being eliminated unchanged. Urinary excretion of radioactivity was bi-phasic with half-lives of 3.1 and 42 hours.

When barriers to absorption are by-passed by intravenous administration, the source chemical has been found to distribute mainly in the liver, lungs and spleen. Excretion of the substance or its metabolites over 14 days was slow with 21.3% and 2.8% of the administered dose found in the faeces and urine, respectively, suggesting a half-life of approximately 40 days. While data from the intravenous route may suggest a possible concern for potential bioaccumulation, the substance is poorly absorbed by the oral route, and the kinetics of urinary elimination suggest a far shorter half-life, indicating a lower potential for bioaccumulation.

An in vitro dermal absorption study using full-thickness skin samples in a Franz diffusion cell system showed that the compound is not systemically bioavailable after dermal exposure. This finding is supported by the results of the IH SkinPerm model. Due to the low vapor pressure, a significant respiratory uptake from airborne vapors can be excluded.

 

Regarding similarities in chemical structures, physico-chemical properties (see below), and in addition results of OECD Toolbox profiling, similar toxicokinetic characteristics are expected for the target substance. This means that the ester bonds of tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate will probably be successively hydrolysed at a low rate in the gastrointestinal tract. The hydrolysis products 2-ethylhexan-1-ol and mono-(2-ethylhexyl) pyromellitate will likely be absorbed to a low extend. 2-Ethylhexan-1-ol but not the mono-ester will undergo further phase-I metabolism. There is no evidence that carboxyl groups of the source and target compounds are modified during phase I-metabolism, or metabolites are produced which play a role for the toxicological behavior of phthalates.

In conclusion, except for the hydrolysis product 2-ethylhexan-1-ol, the biotransformation products or metabolites of the source and target compound are similar as they show the same type but not the same number of functional groups. Available toxicokinetic data may imply that the extend of monoester formation in the gastrointestinal tract, as well as the absorption and systemic bioavailability decreases with an increasing number of ester bonds (2 ester bonds occur in phthalates, 3 in the source substance, 4 in the target substance). Therefore, it seems to be plausible that the gastrointestinal absorption of hydrolysis products of the target substance, i.e. the potential metabolites 2-ethylhexan-1-ol and mono-(2-ethylhexyl) pyromellitate, is very low. The latter metabolite will possibly not undergo a phase-I metabolism but rather be excreted unchanged in the urine, similarly to mono-(2-ethylhexyl) trimellitate. Especially due to low water solubility < 1 mg/L, the target substance is predicted by the IH SkinPerm model to be not absorbed through the skin. The low volatility of the target substance as well as the octanol-water partition coefficient (log Po/w of 6.01) will obviate a significant respiratory uptake.

So in summary, taking into account the above mentioned facts, the following absorption rates may be estimated and applied in subsequent risk assessment while performing route-to-route extrapolations:

- Absorption via oral route: 100% (worst case value due to very limited absorption)

- Absorption via inhalative route: 100% (worst case)

- Absorption via dermal route: 10% (for substances with molecular masses above 500 and LogPow values outside the range of 1-4; refer to R.7c)

Reference 2

Endpoint:

dermal absorption, other

Remarks:

in silico

Type of information:

(Q)SAR

Remarks:

IH Skin Perm

Adequacy of study:

key study

Study period:

June 2016

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

Estimation method using accepted and valid (Q)SAR method.

Principles of method if other than guideline:

The rate of mass build-up (or loss) on the skin comes from the deposition rate onto the skin minus the absorption rate into the Stratum Corneum (SC) and the amount evaporating from the skin to the air.

IH Skin Perm provides two primary dermal exposure modes to the modeler. The first is “instantaneous deposition” in which the substance is assumed to be on the skin as the result of a single exposure event. The second is “deposition over time” in which the substance is assumed to be applied at a constant rate over time. In the first case (instantaneous deposition) the above DepositionRate is zero and IH Skin Perm then works to keep track of this single dose over time as it is absorbed into the SC or evaporates from the surface of the skin. In the second case (deposition over time) the rate of the substance going to the skin is assumed constant and the thickness of the film on the skin will either increase or decrease with time depending on the relative rates of deposition and removal.

The user inputs the amount going onto the skin as a single dose or as a constant rate and IH SkinPerm calculates the amount of chemical absorbed into the SC over time until all the material disappears from the surface via absorption and evaporation or the exposure is considered to be over.
Ultimately, the program estimates the amount of chemical absorbed into the systemic circulation of the body using clearly defined assumptions.
IH SkinPerm does all of this using relatively few physical chemical inputs for the substance. The details of these calculations are all available from Dr. ten Berge (ref: specific documents (http://home.planet.nl/~wtberge/qsarperm.html).

GLP compliance:

no

Remarks:

Computer model

Specific details on test material used for the study:

CAS 3126-80-5
EC 221-508-0
Molecular weight: 703
Temperature: 25 °C
Vapour Pressure:
Water solubility:
Log Kow (skin, pH= 5.5):
Density: 988.5 mg/cm3 (exp.)

Key result

Time point:

1 h

Dose:

1 mg/cm-2/h to 2000 cm-2 skin area

Parameter:

rate

Absorption:

0 mg cm-2 h-1

Key result

Time point:

1 h

Dose:

1 mg/cm-2/h to 2000 cm-2 skin area

Parameter:

amount

Absorption:

0.002 other: mg

Key result

Time point:

1 h

Dose:

of 1 mg/cm-2/h to 2000 cm-2 skin area

Parameter:

percentage

Absorption:

0 %

Conclusions:

Absorbed fraction: 0.0000824%
Amount absorbed: 0.00165 mg
Maximum dermal absorption: 1.03 x 10-6 mg/cm2/h
Dermal/respiratory uptake ratio (from airborne vapor): 0.032

The dermal absorption of tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate is expected to be negligible.

Executive summary:

The dermal absorption of the test item was calculated with IH SkinPerm model of dermal absorption (v. 2.0) as provided by the American Industrial Hygiene Association (AIHA): Calculation of the absorbed fraction as a result of dermal deposition at a rate of 1 mg/cm²/h to 2000 cm²skin area (hands and forearms) during 1 h. The calculation is based on molecular weight of 702.5 g/mol, vapor pressure of 0.00209 Pa (MPBPWIN™ by EPI Suite v.4.1), water solubility of 1 mg/L (exp.), an octanol-water partition coefficient of Log Po/w 6.01 (exp.), density of 0.9908 mg/cm³(exp.) and a melting point of -34 °C (exp.) of the test item.

The calulated values are as follows:

Absorbed fraction: 0.0000824%

Amount absorbed: 0.00165 mg

Maximum dermal absorption: 1.03 x 10^-6mg/cm²/h

Dermal/respiratory uptake ratio (from airborne vapor): 0.032

The dermal absorption of tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate is negligible and the compound is expected to be not systemically bioavailable after dermal exposure .

Description of key information

In order to assess the toxicokinetic behaviour of tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate the available physico-chemical and toxicological data for it and its near read across substances have been evaluated.

Hydrolysis by esterases is considered to be an important first step in the oral absorption of ortho-phthalates. The potential for such hydrolysis to occur with the source substance tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate has been examined in an in-vitro study using rat gut homogenate. There was no evidence of hydrolysis occurring wheras the corresponding phthalate, bis(2-ethylhexyl) phthalate (abbreviation DEHP, EC No 204-211-0, CAS No 117-81-7), was significantly hydrolysed.

The absorption, distribution, metabolism and elimination of the radiolabeled source substance have been investigated in the rat following oral administration of a single dose. Recovery of the administered dose was 94%, with approximately 75% eliminated unchanged in the faeces, 16.3% found in the urine and 1.9% in expired air. Residual radioactivity in the carcass after 6 days was <0.6% of the administered dose. Findings indicate that the compound may be partially hydrolysed in the gastro-intestinal tract to 2-ethylhexan-1-ol and the corresponding di-ester and, following further hydrolysis, the mono-ester. Only 2-ethylhexanol and a single isomer of the monoester (i.e. mono-(2-ethylhexyl) trimellitate) appear to be absorbed. Following absorption, 2-ethylhexanol was extensively metabolised with metabolites eliminated in the urine and as expired¹⁴CO₂. There was no evident metabolism of mono-(2-ethylhexyl) trimellitate, this being eliminated unchanged. Urinary excretion of radioactivity was bi-phasic with half-lives of 3.1 and 42 hours.

When barriers to absorption are by-passed by intravenous administration, the source chemical has been found to distribute mainly in the liver, lungs and spleen. Excretion of the substance or its metabolites over 14 days was slow with 21.3% and 2.8% of the administered dose found in the faeces and urine, respectively, suggesting a half-life of approximately 40 days. While data from the intravenous route may suggest a possible concern for potential bioaccumulation, the substance is poorly absorbed by the oral route, and the kinetics of urinary elimination suggest a far shorter half-life, indicating a lower potential for bioaccumulation.

An in vitro dermal absorption study using full-thickness skin samples in a Franz diffusion cell system showed that the compound is not systemically bioavailable after dermal exposure. This finding is supported by the results of the IH SkinPerm model. Due to the low vapor pressure, a significant respiratory uptake from airborne vapors can be excluded.

 

Regarding similarities in chemical structures, physico-chemical properties (see below), and in addition results of OECD Toolbox profiling, similar toxicokinetic characteristics are expected for the target substance. This means that the ester bonds of tetrakis(2-ethylhexyl) benzene-1,2,4,5-tetracarboxylate will probably be successively hydrolysed at a low rate in the gastrointestinal tract. The hydrolysis products 2-ethylhexan-1-ol and mono-(2-ethylhexyl) pyromellitate will likely be absorbed to a low extend. 2-Ethylhexan-1-ol but not the mono-ester will undergo further phase-I metabolism. There is no evidence that carboxyl groups of the source and target compounds are modified during phase I-metabolism, or metabolites are produced which play a role for the toxicological behavior of phthalates.

In conclusion, except for the hydrolysis product 2-ethylhexan-1-ol, the biotransformation products or metabolites of the source and target compound are similar as they show the same type but not the same number of functional groups. Available toxicokinetic data may imply that the extend of monoester formation in the gastrointestinal tract, as well as the absorption and systemic bioavailability decreases with an increasing number of ester bonds (2 ester bonds occur in phthalates, 3 in the source substance, 4 in the target substance). Therefore, it seems to be plausible that the gastrointestinal absorption of hydrolysis products of the target substance, i.e. the potential metabolites 2-ethylhexan-1-ol and mono-(2-ethylhexyl) pyromellitate, is very low. The latter metabolite will possibly not undergo a phase-I metabolism but rather be excreted unchanged in the urine, similarly to mono-(2-ethylhexyl) trimellitate. Especially due to low water solubility < 1 mg/L, the target substance is predicted by the IH SkinPerm model to be not absorbed through the skin. The low volatility of the target substance as well as the octanol-water partition coefficient (log Po/w of 6.01) will obviate a significant respiratory uptake.

So in summary, taking into account the above mentioned facts, the following absorption rates may be estimated and applied in subsequent risk assessment while performing route-to-route extrapolations:

- Absorption via oral route: 100% (worst case value due to very limited absorption)

- Absorption via inhalative route: 100% (worst case)

- Absorption via dermal route: 10% (for substances with molecular masses above 500 and LogPow values outside the range of 1-4; refer to R.7c)

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Absorption rate - oral (%):

100

Absorption rate - dermal (%):

10

Absorption rate - inhalation (%):

100