Tris(2-ethylhexyl) phosphate

Endpoint summary

Description of key information

A full suite of environmental fate studies have been conducted on the substance in order to meet the data requirements under Annexes VII to X of REACH. The results of these studies are summarised below:

 

Hydrolysis

In a single key study, the stability to hydrolysis of Tris(2-ethylhexyl) phosphate was performed at pH 4, pH 7 and pH 9 in accordance with OECD 111 (Severino, 2013).. The study was conducted with Tris (2-ethylhexyl) phosphate technical grade for five days for 50 ± 0.5. In a preliminary test conducted at 50 ± 0.5 °C, it were found that at pHs 4, 7 and 9, the Tris(2-ethylhexyl) phosphate concentration did not decrease more than 10 % during an incubation period of 5 days. Tris(2-ethylhexyl) phosphate is considered stable with half-life longer than one year (t1/2 > 1 year).

 

Phototransformation in Water

In a single key study, an assessment of photolysis was conducted according to OECD 316 (Severino, 2013). The test substance showed varying half-lives dependent on pH. However all photolytic degradation half-lives were under 4 days. Half-lives were 0.93 days (pH 4), 1.64 days (pH 7) and 3.50 days (pH 9). Validity/ quality criteria were met in accordance with those documeted by the OECD test guideline. Two degradation products were identified, and were 2-ethyl hexanol and 2 -ethyl hexanoic acid. Tris(2 -ethylhexyl)phosphate is photolytically unstable at all tested pH levels.

 

Biodegradation in Water: Screening Tests

A weight-of-evidence is presented for biodegradation in water: screening tests, consisting of 4 ready biodegradability studies.  In a modified OECD 301B study (Simon, 2017) conducted with a radiolabelled test item, the biodegradability of the test item was assessed over a 56 day period.  The radiolabelled test item consisted of three 14C atoms located at the alpha position relative to the phosphate group on each alkyl chain.  This study was commissioned to investigate whether the low water solubility (0.14 μg/L) was the rate limiting factor in the other existing ready biodegradability studies (Schroder, 2014; Bidinotto, 2013; Anon, 1992), limiting the bioavailability of the test item to the organisms when the standard addition rate of 10-20 mg C/L is used.  In this study use of radiolabelled material permitted the use of a much lower addition rate (1 μg/L test item) without compromising detection of evolved carbon dioxide.

 

The test medium was inoculated with microorganisms from a digester of a sewage treatment plant mainly fed with municipal wastewater. The test solutions were aerated by the passage of CO2 free air at a controlled rate in closed flasks at 22 °C for 56 days. The rate of degradation was monitored by measuring the 14C- carbon dioxide produced from degradation of the 14C-labelled test item. To monitor the validity of the test conditions, also carbon dioxide release of inoculum blank assays and a procedural control containing unlabelled sodium benzoate were applied. For the test item, the amount of 14C-carbon dioxide produced from the test substance was expressed as a percentage of the 14C-atoms present in the test item at test start. For the procedural control, the amount of carbon dioxide produced from the reference substance sodium benzoate (corrected for that derived from the blank inoculum) is expressed as a percentage of the ThCO2.

 

The mineralization of 14C-Tris(2-ethylhexyl) phosphate in the static test - based on the radiolabelled carbon elements in the molecule - was found to be 0.76 % after 28 days and 1.2 % after 56 days. Consequently, mineralization within the 10-day-window could not be calculated. Since only three carbon atoms in the centre of the molecule out of a total number of 24 carbon elements are labeled, it has to be stated that a possible primary degradation with a mineralization of up to 87.5 % of the lateral carbon elements could not be detected in the test design applied. This test design shows that there is a maximum of 1.2 % of total mineralization of 14C-Tris(2-ethylhexyl) phosphate.

 

The maximum biodegradation observed for the substance in ready biodegradability screening tests with standard addition rates was 14 % (Schroder, 2014).

 

Based on the available studies for this endpoint, we can conclude that the substance is not considered readily biodegradable under standard OECD 301 test conditions.  Additionally, we can conclude that up to 1 % of the carbon atoms located at the alpha position relative to the phosphate group on each alkyl chain will mineralise when the substance is added to an OECD 301B test design at 1 μg/L (7 times the water solubility, although the solubility in mineral media spiked with inoculum is expected to be lower).  The available data cannot rule out primary biodegradation and mineralisation of the alkyl chains beyond the alpha carbon when added to OECD 301B test system using test item addition rates closer to the solubility limit, nor can it rule out adsorption of the test item to glassware or organic particulates in the test system, which may also affect performance of this test.

 

The conclusion drawn is that the substance does not meet the criteria for ready biodegradability under the strict conditions of OECD 301 screening methodologies.

 

Soil simulation

The aerobic transformation of ¹⁴C-Tris(2-ethylhexyl) phosphate in four soils was performed in accordance with the OECD Guideline for Testing of Chemical No. 307 "Aerobic and Anaerobic Transformation in Soil” (2002) in response to ECHA Compliance CHeck decision (CCH-D-2114465573-43-01/F).

The study was conducted under aerobic condition at 12ºC for 120 days. Mass balance for all samples was between 90-110 %. The amount of parent in soils extracts was recorded at each timepoint by HPLC. No major metabolites were observed during the test.

DT50 and DT90 kinetics were determined for the parent compound with SFO deemed the best fit for all soil types. The DT50 geometric mean was 769 days (range: 436 - 1620 days).

 

Bioaccumulation

A bioaccumulation study in fish (OECD TG 305) is currently on-going in the framework of ECHA Compliance CHeck decision (CCH-D-2114465573-43-01/F).

Using a weight of evidence approach it has been demonstrated that the substance tris(2 -ethylhexyl) phosphate does not meet the criteria for a bioaccumulative substance, in accordance with Annex XIII of REACH.

 

In a study conducted equivalent to OECD 305 common carp (Cyprinus carpio) were exposed to two aqueous concentrations of tris(2-ethylhexyl) phosphate (0.2 and 2 mg/L) for 42 days.  Water solubility was aided by the use of suitable levels of acetone.  No significant uptake was shown after 42 days, so the study was terminated.  The maximum bioconcentration factor (BCF) determined in the study was 22 L/kg in the 0.2 mg/L dose group.  The range of BCF values determined throughout the study were 2.4 – 22 L/kg. Given the age of this study and some deficiencies compared to the most recent OECD 305 Guideline, the study has been assigned a Klimisch rating of 2 (reliable with restrictions). However, regarless of some relatively minor deficiencies from the current OECD 305 Guideline, the lack of significant uptake of TEHP over 42 days is a reliable indication of the bioaccumulating potential of this substance.

 

In support of thein vivo OECD 305 study, a series of BCF (Q)SARs were used in support of the conclusion drawn in the fish study. The following table summarises the results of the predicted BCF values.

 

Bioconcentration factor (Q)SAR data for tris(2 -ethylhexyl) phosphate

(Q)SAR	BCF	Applicability Domain
BCFBAF (v3.01)	30.34 L/kg	in domain
BCFmax (Dimitrov et al., 2005)	336 L/kg	in domain

 

The weight-of-evidence, consisting of 3 reliable, discreet assessments of the BCF of tris(2-ethylhexyl) phosphate, indicate that the substance does not meet the criteria for B or vB (BCF is <2,000 L/kg).  This weight-of-evidence approach is consistent with ECHA Guidance on Information Requirements and Chemical Safety Assessment, Chapter R,7c, Section R.7.10.6. Integrated Testing Strategy for Aquatic Bioaccumulation, and Chapter R.11 PBT Assessment.

 

Adsorption / Desorption

Two acceptable (Q)SAR predictions for tris(2 -ethylhexyl) phosphate indicate that the soil adsorption coefficient (Koc) is >10,000 L/kg. When used in exposure modelling, a Koc of 6,000 L/kg results in close to 99 % adsorption and doesn't significantly rise with increasinf Koc. Therefore, the generally accepted limit value of Koc = 10,000 L/kg is used for chemical safety assessment, which is the limit value for EUSES modelling.

 

Additional Information on Environmental Fate and Behaviour (Identification of Degradation Products)

The EAWAG-BBD Pathway Prediction System predicts the following highest likelihood biological degradation pathway for tris(2-ethylhexyl) phosphate:

Tris(2 -ethylhexyl) phosphate -> 2 -ethylhexanol -> 2 -ethylhexanoic acid

Intermediate degradation products may include bis(2 -ethylhexyl) hydrogen phosphate and 2 -ethylhexyl hydrogen phosphate.

Additional information

Identification of Degradation Products (REACH Annex IX, Section 9.2.3)

When a substance is not fully mineralised, but degraded into other substances, the PBT/vPvB properties of these should be evaluated before a final judgement of whether the parent substance fulfils the PBT/vPvB criteria. This endpoint is fulfilled through a weight of evidence argument based on observations in the phototransformation in water study (Severino, 2013) and metabolic profiling of the substance in soil using the EAWAG-BBD pathway prediction system.

In a phototransformation study conducted in accordance with OECD Guideline 316 (Severino, 2013), the substance was considered to be photolytically unstable.  The study has been assigned a Klimisch rating of 1, the study was conducted in accordance with international guidelines in a GLP facility, and all validity criteria were fulfilled.    The test solution (solution A) of tris(2-ethylhexyl) phosphate was prepared by dissolving 4.2 mg of test substance (98.99%) in 1 mL of tetrahydrofuran (solubility aid) in a 100 mL volumetric flask and making to volume with Milli-Q water. The concentration of tris(2-ethylhexyl) phosphate in the Solution A was 41.57 mg L-1.  To prepare the solution at pH's 4 (solution B), 7 (solution C) and 9 (solution D), an aliquot of 25 mL of each buffered solution was mixed with 25 mL of Solution A, giving around 20.78 mg L-1.  Buffered solutions for each pH were prepared and covered with aluminum foil.  Flasks were filled to the top leaving no headspace to minimize volatilization. All preparation steps were carried out inside a laminar flow chamber in order to avoid microbiological contamination.  Sample tubes were placed in artificial sunlight inside a Suntest XLS + unit. This unit was fitted with a Xenon-arc lamp (250W.m-2) and a special UV-glass filter, which eliminate light with wavelengths lower than 290 nm.  The irradiance inside the chamber was monitored by a sensor (lighmeter).  The temperatures and pH of the samples were also monitored during the test.  Sampling was conducted on eight occiasions between days 0 and 7, each sampling event collected four aliquots of 1.0 mL, two from sample flask and two from control flask. Immediately after collecting the samples were stored in freezer at -20°C until analysis. The quantification of Tris(2-ethylhexyl) phosphate and degradation products was performed by gas chromatography Agilent GC 6890 with mass spectrometty MS 5973.  Identification of degradation products was also supported by the analysis of reference standards, the identification was performed by comparison between retention times in an Agilent GC 6890 with mass spectrometry MS 5973. The half-life of tris(2-ethylhexyl) phosphate was determined to be 0.93 days at pH 4, 1.64 days at pH 7 and 3.50 days at pH 9.  The temperature ranged between 20.7 °C and 21.5 °C for pH's 4, 7 and 9. The irradiance ranged between 31.80 and 34.62 Klux for pH's 4, 7 and 9. Two degradations products were identified in the study, 2-ethylhexanol and 2-ethylhexanoic Acid.  In accordance with the results, with decreasing of concentration of tris(2- ethylhexyl) phosphate, there was an increasing of concentration of 2-thylhexanol and when the concentration of 2-ethylhexanol decreased, there was increase in the concentration of 2-ethylhexanoic acid.  The results indicate that the degradation pathway for tris(2-ethylhexyl) phosphate results in transformation to 2-ethylhexanol, which subsequently transforms to 2-ethylhexanoic acid.

In addition to assessment of abiotic transformation, the Registrant assessed biologically mediated transformation of the chemical substance using the EAWAG-BBD Pathway Prediction System, which predicts pathways for microbial degradation of chemical compounds. Predictions use biotransformation rules, based on reactions found in the EAWAG-BBD database or in the scientific literature.  The BBD database contains information on microbial biocatalytic reactions and biodegradation pathways for primarily xenobiotic chemical compounds. The goal of the EAWAG-BBD is to provide information on microbial enzyme-catalyzed reactions that are important for biotechnology.  The reactions covered are studied for basic understanding of nature, biocatalysis leading to specialty chemical manufacture, and biodegradation of environmental pollutants.  Individual reactions and metabolic pathways are presented with information on the starting and intermediate chemical compounds, the organisms that transform the compounds, the enzymes, and the genes.

The EAWAG-BBD Pathway Prediction System predicts the following highest likelihood biological degradation pathway for tris(2-ethylhexyl) phosphate:

Tris(2 -ethylhexyl) phosphate -> 2 -ethylhexanol -> 2 -ethylhexanoic acid

Intermediate degradation products may include bis(2 -ethylhexyl) hydrogen phosphate and 2 -ethylhexyl hydrogen phosphate.

Primary transformation from tris(2 -ethylhexyl) phosphate to the intermediate products bis(2 -ethylhexyl) hydrogen phosphate and 2 -ethylhexyl hydrogen phosphate, with subsequent cleavages forming 2 -ethylhexanol occurs via the following reaction pathways:

Rule bt0361

aliphatic Phosphoester -> Alcohol

aliphatic Phosphodiester -> Alcohol + aliphatic Phosphoester

aliphatic Phosphotriester -> Alcohol + aliphatic Phosphodiester

aliphatic Thiophosphoester -> Alcohol + aliphatic Thiophospate

This is based on the following EAWAG-BBD Database Reactions:

1,5-Anhydro-D-glucitol -----> 1,5-Anhydro-D-glucitol-6-phosphate (reacID# r1784)

S-(Diethylsuccinyl)-O-methylphosphorothioate -----> Methanol + S-(Diethylsuccinyl)-phosphorothioate (reacID# r1716)

Diethylthiophosphoric acid -----> Ethanol + Ethylthiophosphate (reacID# r1668)

O,S-Dimethyl hydrogen phosphorothioate -----> Methanol + S-Methyl dihydrogen phosphorothioate (reacID# r1711)

Dimethylphosphate -----> Methanol + Methylphosphate (reacID# r1691)

Dimethylthiophosphate -----> Methanol + Methylthiophosphate (reacID# r1684)

Ethylphosphate -----> Ethanol + Phosphate (reacID# r1662)

Malaoxon -----> Methanol + S-(Diethylsuccinyl)-O-methylphosphorothioate (reacID# r1715)

Malathion -----> Methanol + Desmethyl malathion (reacID# r1687)

Methylphosphate -----> Methanol + Phosphate (reacID# r1692)

Methylphosphate -----> Methanol + Phosphate (reacID# r1714)

Methylthiophosphate -----> Methanol + Thiophosphate (reacID# r1685)

Transformation of the primary alcohol formed is then mediated by the following reaction pathway:

primary Alcohol -> Aldehyde

This is based on the

following EAWAG-BBD Database Reactions:

Benzyl alcohol -----> Benzaldehyde (reacID# r0267)

cis-3-Chloro-2-propene-1-ol -----> cis-3-Chloroallyl aldehyde (reacID# r0691)

trans-3-Chloro-2-propene-1-ol -----> trans-3-Chloroallyl aldehyde (reacID# r0690)

2-Chloroethanol -----> Chloroacetaldehyde (reacID# r0002)

2,2-bis(4'-Chlorophenyl)ethanol (DDOH) -----> bis(4'-Chlorophenyl)acetate (DDA) (reacID# r0518)

Citronellol -----> Citronellal (reacID# r1155)

p-Cumic alcohol -----> p-Cumic aldehyde (reacID# r0393)

2,3-Dihydroxy-2-methyl propionate -----> 2-Hydroxy-2-methyl-1,3-dicarbonate (reacID# r0620)

1-Dodecanol -----> Dodecanal (reacID# r0603)

Ethanol -----> Acetaldehyde (reacID# r0172)

Furfuryl alcohol -----> Furfural (reacID# r1433)

Geraniol -----> Geranial (reacID# r1163)

1-Hydroxy-4,4-dimethylpentan-3-one -----> 4,4-Dimethyl-3-oxopentanal (reacID# r1308)

3-Hydroxybenzyl alcohol -----> 3-Hydroxybenzaldehyde (reacID# r0400)

6-Hydroxyhexanoate -----> 6-Oxohexanoate (reacID# r0174)

1-Hydroxymethylnaphthalene -----> 1-Naphthaldehyde (reacID# r0786)

2-Hydroxymethylnaphthalene -----> 2-Naphthaldehyde (reacID# r0771)

2,2-bis(4-Hydroxyphenyl)-1-propanol -----> 2,2-bis(4-Hydroxyphenyl)-1-propanoate (reacID# r0863)

4-Hydroxytoluene -----> 4-Hydroxybenzaldehyde (reacID# r0272)

Methanol -----> Formaldehyde (reacID# r0238)

2-Methyl-2-hydroxy-1-propanol -----> 2-Methyl-2-hydroxypropanal (reacID# r0616)

2-Methylbenzyl alcohol -----> 2-Methylbenzaldehyde (reacID# r0221)

3-Methylbenzyl alcohol -----> 3-Methylbenzaldehyde (reacID# r0213)

p-Methylbenzyl alcohol -----> p-Tolualdehyde (reacID# r0176)

Myrtenol -----> Myrtenal (reacID# r0710)

1-Octanol -----> 1-Octanal (reacID# r0022)

Perillyl alcohol -----> Perillyl aldehyde (reacID# r0729)

3-Phenoxylbenzyl alcohol -----> 3-Phenoxybenzaldehyde (reacID# r1766)

Pivalate -----> Dimethylmalonate (reacID# r1038)

4-Pyridoxate -----> 2-Methyl-3-hydroxy-5-formylpyridine-4-carboxylate (reacID# r1520)

4-Sulfobenzyl alcohol -----> 4-Sulfobenzaldehyde (reacID# r0291)

N,N-diethyl-3-(hydroxymethyl)benzamide -----> N,N-diethyl-3-formylbenzamide (reacID# r1839)

Pyridoxine -----> Isopyridoxal (reacID# r1525)

Pyridoxine -----> Pyridoxal (reacID# r1516)

Pyridoxine -----> Pyridoxal (reacID# r1538)

Trichloroethanol -----> Trichloroacetate (reacID# r0489)

2,4,4-Trimethyl-1-pentanol -----> 2,4,4-Trimethylpentanal (reacID# r1270)

Vanillyl alcohol -----> Vanillin (reacID# r0651)

The data presented highlight that whether the transformation of the parent tris(2-ethylhexyl) phosphate is abiotically- or biotically-mediated, the transformation products are expected to be the same.  Both 2-ethylhexanol and 2-ethylhexanoic acid are readily biodegradable and are not classified as dangerous to the environment under the CLP Regulation.  It is therefore concluded that the transformation products are not a concern for the PBT assessment or environmental risk assessment of the parent substance.