Bis(2-ethylhexyl) tetrabromophthalate

Endpoint summary

Description of key information

Physicochemico data, in-vitro and limited in vivo studies, as well as toxicological studies indicate a low bioaccumulation potential of bis(2-ethylhexyl) tetrabromophthalate. As metabolites only minor amounts of mono(2-ethylhexyl) tetrabromophthalate (TBMEHP) and tetrabromo phthalic acid (TBPA) were found.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

Bis(2-ethylhexyl) tetrabromophthalate (TBPH) is an organic liquid (melting point -27°C) with a MW of 706.2 g/mol and a high boiling point (calculated boiling point = 539.75°C (at 1013 hPa)). The QSAR determination of the vapour pressure of the substance using the model MPBPWIN included in the Estimation Program Interface (EPI) Suite v4.11 revealed a value of 3.56E-7 Pa at 25°C. Due to the low vapour pressure and high boiling point human exposure via the inhalation route is assumed to be limited.

The calculated values for water solubility is 1.983E-9 mg/L at 25°C and 11.95 for Log Pow (according High Production Volume (HPV) challenge Program, Test Plan for Phthalic acid tetrabromo bis 2-ethylhexyl-ester (CAS #26040 -51 -7). In an experimental study, the water solubility of the substance could not be detected without solubilizer and is reported to be < 0.05 µg/l at 20°C. The partition coefficient of the substance determined by HPLC was log Pow = 10.2 at 25°. Based on these values there is no evidence of absorption due the insolubility of the substance in water and the high octanol-water partition coefficient.

TBPH has very low acute toxicity (discriminating dose oral > 5000 mg/kg bw and discriminating dose dermal > 2000 mg/kg bw (highest applied doses). TBPH is not irritating to skin and eyes and not sensitizing.

In a subacute toxicity study with TBPH doses of 200, 2 000 or 20 000 ppm (= ca. 21.97, 223.4 or 2331 mg/kg/day) there were no significant changes in clinical signs, clinical chemistry, hematology, organ weights, or histopathology. None of the animals died due to the application of the test substance. Slightly low overall bodyweight gain was recorded for females receiving the highest dietary concentration of the test item. Males treated with the test substance were unaffected. Marginally low alanine amino-transferase activities were seen in females receiving the highest dietary concentration of the test substance, and marginally low phosphorus concentrations were seen in all females and males receiving the highest dietary concentration of the test substance.

In a subchronic 90 day repeated dose toxicity study according to OECD 408, oral administration of Bis(2-ethylhexyl) tetrabromophthalate (CAS No. 26040-51-7) to male and female Wistar Han™:RccHan™:WIST strain rats for ninety consecutive days at dose levels of 100, 300 and 1000 mg/kg bw/day resulted in no treatment related changes.  The No Observed Effect Level (NOEL) is considered to be 1000 mg/kg bw/day, the highest dose tested.

TBPH (called BEH-TEBP in this study) was administered to 4 female SD rats per dose by oral gavage at 0.1 or 10 µmol/kg, and to 4 male B6C3F1/Tac mice at 0.1 µmol/kg. The doses correspond to 0.07 (0.1 µmol/kg) and 7 mg/kg bw (10 µmol/kg). Disposition and elimination was assessed (Knudsen et al., 2014 and 2017). The results of the current studies indicate poor absorption and rapid elimination of BEH-TEBP as parent compound. 92-98% of the radioactive compound was found unchanged in feces after oral administration to mice and rats. A minor amount of each dose (0.8-1%) was found in urine after 82 hours.

To determine disposition and elimination of systemically available TBPH, TBPH was injected as a single intravenous bolus dose of 0.1 µmol/kg to the SD rats (Knudsen et al., 2017). IV-administeredTBPH was slowly eliminated in feces, with > 15% retained in tissues after 72 h. Bile and feces contained the metabolite mono-ethylhexyl tetrabromophthalate.

Subsequent studies on four female SD rats with 10 daily oral doses of 0.1 µmol/kg radioactive TBPH were initated by Knudsen et al. (2017) to determined the bioaccumulation potential of TBPH. Tissues and excreta were collected 24 h after the last treatment and racioactivity recoveries were recorded. Also after repeated oral exposure elimination occurred mainly via feces (nearly 100%). Only a small amount of TBPH was recovered in urine (about 0.6%). Thus, absoption was shown to be very poor. Radioactivity was recorded in tissues, e.g. in liver and adrenals with 113 and 207 pmol-eq/g, respectively. This accounts to 0.4% and 0.01% of the cumulated administered dose, respectively.

A parallelogram approach was used by Knudsen et al., (2016) to predict human dermal absorption and flux for TBPH (called BEH-TEBP in this study). [14C]-TBPH was applied to full thickness skin of 4 human individuals and of 4 rats at 100 nmol/cm2 in toluene using a flow-through system. Intact rats received analogous dermal doses. Treated skin was washed and tape-stripped to remove “unabsorbed” [14C]-radioactivity after continuous exposure (24 h). “Absorbed” was quantified using dermally retained [14C]-radioactivity; “penetrated” was calculated based on [14C]-radioactivity in media (in vitro) or excreta + tissues (in vivo).

TBPH in vitro penetrance was minimal (< 0.01%) for rat or human skin. TBPH absorption was 12± 11% for human skin and 41± 3% for rat skin. In vivo, total absorption was 27±9%; 1.2% reached systemic circulation. In vitro maximal TBPH flux was 0.3±0.2 and 1±0.3 pmol-eq/cm²/h for human and rat skin; in vivo maximum flux for rat skin was 16±7 pmol-eq/cm2/h. TBPH-derived [14C]-radioactivity in the perfusion media could not be characterized. Only <1% of the dose of TBPH is estimated to reach the systemic circulation following human dermal exposure under the conditions tested.

In a metabolism study rats received by gavage 500 mg/kg bw (125 mg/250 mg bw) of technical grade Uniplex FRP-45 (> 95% TBPH) in corn oil (Silva et al., 2015). No TBPH or oxidative metabolites were reported in urine or serum. TBPA (2,3,4,5-tetrabromo phthalic acid) was identified as an in vivo urinary and serum metabolite (mean urinary levels ca. 0.5 mg/liter and mean serum levels ca. 0.05 mg/liter). The rats used in the experiment weighing ca. 250 g. Assuming that the rats produced ca. 20 ml urine per day, about 0.01 mg in 20 ml were found. This means, about 0.008 % TBPA (tetrabromo phthalic acid) was found in the urine within 24 hours after application. Assuming a blood volume of 10 % (equivalent to ca. 5% serum) in the rat, this correlates with 50 ml serum per kg/bw (12.5 ml/250 mg bw). This means, of the 125 mg test substance per rat about 0.0005% was detected as TBPA after 48 h in the rat serum. Additionally, TBBA (2,3,4,5-tetrabromo benzoic acid; mean urinary levels ca. 45.6 mg/l and mean serum levels ca. 1.2 mg/l), a known metabolite of 2-ethylhexyl-2,3,4,5-tetrabromo-benzoate was detected at concentrations much higher than TBPA (2,3,4,5-tetrabromo phthalic acid), even thought TBPH was the main component of Uniplex FRP-45 (> 95%) and 2-ethylhexyl-2,3,4,5-tetrabromo-benzoate was only a minor constituent (<< 5%). Because Uniplex-45 was technical grade and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate was present in the formulation, 2,3,4,5-tetrabromobenzoic acid likely resulted from the metabolism of 2-ethylhexyl-2,3,4,5-tetrabromobenzoate. The authors “hypothesized that because of its relatively low solubility and high molecular weight, BEH-TEBP [=TBPH] may excrete preferentially unchanged in feces. Regrettably, we did not collect feces for this experiment” (Silva et al 2015). Due to the above mentioned limitation and insufficient characterization of the test compound (Uniplex 45-FRP) the reliability of the study is limited.

In experiments with human liver microsomes (HLM) of Roberts et al. (2012), a significant loss of TBPH was not observed, and no metabolites were detected by GC/MS analysis of the sample extracts. An LC/MS-MS method was developed to monitor mono(2-ethylhexyl) tetrabromophthalate (TBMEHP), a potential hydrolysis metabolite of TBPH. After a 6-h incubation with HLM, TBMEHP was not detected as a metabolite of TBPH, and no significant loss of TBPH was observed. However, TBPH was slowly metabolized to form TBMEHP in the presence of 0.1mg/mL of porcine hepatic carboxylesterase (PCE). This reaction was monitored at multiple time points up to 6 h and maintained linearity at an approximate rate of 1.08 pmol/min/mg esterase.

In a previous study with PCE, DEHP (50 μM) was metabolized to form MEHP at a rate of 127 pmol/min/mg protein. This rate was approximately 100 times faster than the hydrolysis of TBPH observed in this study (1.08 pmol/min/mg protein).

The prominent difference between the metabolic hydrolysis of DEHP and TBPH may be a result of steric hindrance by the fully brominated phenyl ring of TBPH.

Altogether, no metabolites of TBPH were observed with HLM in vitro. From this study there is no indication that TBPH is degraded to TBMEHP in vivo. In an in-vitro experiment the hydrolysis rate of TBPH with PCE is by factor 100 slower compared with DEHP.

Overall, for the human health risk assessment it can be assumed that TBPH is unreactive, insoluble, not inhalable and there is no evidence of significant absorption and no evidence of severe toxicity in a 28-day study at doses above the limit dose. In a subchronic 90 day repeated dose toxicity study no treatment related changes were found.  The No Observed Effect Level (NOEL) is considered to be 1000 mg/kg bw/day, the highest dose tested.