Tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate

Endpoint summary

Description of key information

Distribution in environmental compartments has been calculated using a Fugacity model according to Mackay, Level III. Soil and sediments were found to be the major target compartments.

 

If released to air, a calculated vapour pressure of 6.8E-10 hPa at 20 °C indicates that the substance will exist mainly in the particulate phases in the ambient atmosphere. Any material in the vapour-phase will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air estimated to be ca. 12 hours. Any substance in the particulate-phase will be removed from the atmosphere by wet and dry deposition.

 

If released into water, the substance is expected to adsorb to suspended solids and sediment based upon the measured Koc. Volatilization from water surfaces is not expected to be an important fate process based upon this compound's estimated Henry's Law constant. The hydrolysis half-lives were estimated to be 15.7 years at pH 7 and 57.4 days at pH 9.

 

If released to soil, the substance is expected to have low mobility based upon a measured Koc of 9.1E22 L/kg. Volatilization from moist soil surfaces is not expected to be an important fate process based upon an estimated Henry's Law constant of .0506 Pa m³/mol at 25°C. The substance is not expected to volatilize from dry soil surfaces based upon its estimated vapor pressure.

 

The substance is expected to slowly biodegrade under aerobic conditions and it is possible that the rate of biodegradation may be limited by the rate of hydrolysis of the test substance and/or the rate with which the substance dissolves. Modelling of possible biodegradation pathways indicate that aerobic degradation is likely, the first steps in this being hydrolysis to trimellitic acid and 2 -ethylhexanol, both of which have been shown to be readily biodegradable. Degradation of the registered substance under aerobic conditions has been examined in two aquatic sediment systems at 12°C. One metabolite was formed in both studied water-sediment systems at levels greater than 10 % of the applied radioactivity. This metabolite was identified in both systems as the di-esters of the parent substance, a tri-ester. Minor metabolites were identified as the mono-esters and trimellitic acid together with one other, unidentified, minor metabolite. The DT50 of the parent substance from the two systems was <1 day from the water phase, 39 -54 days from the sediment phase and 16 -25 days from the total system. There was evidence that mineralisation occurs, significant levels of radio-labelled carbon dioxide being measured. The mineralisation rate, based on carbon dioxide production, was 0.126 - 0.166 for both systems. Degradation and dissipation of the substance has been demonstrated to be bi-phasic within a water-sediment system. Dissipation was driven by multiple processes - partition into the water and the sediment phase, initial degradation to di-esters of the parent compound followed by further degradation and formation of carbon dioxide. The registered substance does not fulfil the persistence criterion according to REACH, Annex XIII for fresh water sediment (degradation half-life for fresh water sediment > 120 days) and would not therefore require classification as persistent (P) or very persistent (vP).

 

Bioaccumulation potential has been evaluated in fish according to OECD test methods. A measured BCF of up to 2.7 suggests the potential for bioconcentration in aquatic organisms is low. However, there are some uncertainties in the experimental data mainly due to testing at concentrations above the water solubility of the substance by the use of solubilising agents which are recognised as having the potential to lead to an underestimation of the BCF. Information for the potential of a substance to bioaccumulate within aquatic organisms may be obtained from toxicokinetic studies with mammals, the available information on TOTM indicating that the parent substance is poorly absorbed. Dermal absorption is expected to be negligible (see Section 7.1.2). Studies in the rat (see Section7.1.1) indicate that, following oral administration, hydrolysis to the di-ester and mono-ester with release of 2-ethylhexanol occurs. Modelling to predict likely biodegradation/environmental metabolites indicates the same with complete ester hydrolysis to trimellitic acid and 2-ethylhexanol, both of which are readily biodegradable (See Section 5.2.1 – Biodegradation in water: screening tests – Pathway modelling). Q(S)AR estimate of the bioconcentration factor using the model NTP NICEATM indicate, for the substance itself, 387 L/Kg wet wt:

Extending the estimates of the bioconcentration factor using the EPA Epi Suite, we have:

Di-ester (CAS 58978-43-1): 56.2 L/kg wet wt at default logPow 7.93 and water solubility 0.31μg/L

Mono-ester (CAS 68735-92-2): 3.2 L/kg wet wt at default logPow 4.61 and water solubility 1043μg/L

Trimellitic acid (CAS 528-44-9): 3.2 L/kg wet wt at default logPow 0.95 and water solubility 5963 mg/L

2-ethylhexanol (CAS 104-76-7): 29.5 L/kg wet wt at default logPow 2.73 and water solubility 1379 mg/L

These considerations suggest that the potential for bioaccumulation is low.