Trixylyl phosphate

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

Persistent/very Persistent

The substance displays properties that indicate persistency within the environment, based on low ready biodegradability. Trixylyl phosphate displays a low ready biodegradability in that it achieved 14% biodegradation in a 28-day study closed bottle test. 

The substance is also not expected to hydrolyse under normal environmental conditions. Experimental studies on hydrolytic effects demonstrated that the substance was stable to hydrolysis at environmentally relevant temperature and pH’s, with a half life of > 1year at pH 7. As such, negligible to nil degradation is anticipated via this route. Studies on direct phototransformation in water are not available but it is assumed on the basis of chemical structure that the substance is not degraded by direct photolysis. It is concluded, therefore, that abiotic processes would not contribute significantly to the depletion of the substance within the environment. 

A study was conducted to assess the potential mineralization and transformation of Trixylyl Phosphate in aerobic water systems. HPLC/β-RAM analyses of samples from the live and sterile 200 μg/L treatment groups showed that the parent compound Trixylyl Phosphate remained substantially intact in all live and sterile vessels throughout the course of this study. Additionally there were no transformation products of the parent compound found. The DT50 and DT90 values are reported as >60 days, the duration of the study, confirming that the substance does not undergo mineralization in water.

Due to being not readily biodegradable, and having no significant mechanism of hydrolysis the substance is considered to be persistent. As such, the substance fulfills the requirements of Annex XIII, Para 1.1 based on evaluation of available data, and can be considered to be “P” and “vP” based on this data.

Bioaccumulative/very Bioaccumulative

An assessment of the propensity towards bioaccumulation was undertaken, utilizing appropriate techniques such as:

·        Read across to structural analogues.

·        QSAR derivation, using recognized tools

·        Literature data

The results are as follows:

Read across to Structural Analogues:

Phenol, isopropylated, phosphate (3:1).

As a recently conducted study, this is considered as the key substance for evaluation. The highest BCF of 922 is assigned to the substance from read across to this study.

The substance is not considered to be bioaccumulative, and all BCF’s are less than 1000.

Tricresyl phosphate.

This data is listed on the World Health Organisation website. The paper contains various bioaccumulation assessment studies on this structural analogue and demonstrate thattricresyl phosphate does not demonstrate a propensity towards bioaccumulation, based on the measured values within the studies.

As a weight of evidence approach, it is considered that on structural grounds, the same conclusion can be applied to trixylyl phosphate.

QSARs for substance:

QSAR prediction using BCF model (CAESAR) (Version 2.1.1.11) = BCF 36.0 L/kg based on log(L/kg) 1.56

QSAR prediction using BCF model (Meylan) (version 1.0.0) (CAESAR).= BCF 669.24 L/kg Based on log(L/kg) 2.83

QSAR prediction using BCF Read-Across (version 1.0.0) (CAESAR) = BCF >=118.0 - <=126.0 Based on log(L/kg) 2.07-2.1

QSAR prediction using US EPA On-Line EPI Suite™ v4.0 model BCFBAF = BCF  669.09 L/kg Based on Estimated Log BCF = 2.817

Literature data:

Two studies by Bengtsson et al are presented.

Conclusion:

On the basis of a weight of evidence approach, there is sufficient information available to state that the substance is not bioaccumulative without the need for further testing as requested by ECHA. Results observed across the data available indicate that the substance, as part of the phosphates group, is unlikely to be bioaccumulative within the aquatic environment.

Overall

On the basis of a weight of evidence approach, there is sufficient information available to state that the substance is not bioaccumulative.  

Toxicity

On the basis of effects noted in fish and Daphnia, the substance is deemed to be classified according to Regulation (EC) No 1272/2008 the substance is also classified as:

-        H400: Very toxic to aquatic life with long lasting effects;: Aquatic Acute and Chronic Category 1.

-       H410: Very Toxic to aquatic life with long lasting effects.

No chronic NOEC for the substance currently is available, so determination of this value is not applicable.  However, the substance is also classified as having concern for reproductive toxicity. The results triggered classification under the CLP Regulation (EC No 1272/2008) as follows:

Repr. Cat. 1B:

H360f: May damage fertility <testicular effects > <oral>.

H373: May cause damage to organs <or state all organs affected, if known> through prolonged or repeated exposure <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>. (adrenals, testes, epididymides, ovaries, liver (females only))

As such, the substance fulfils the requirements of Annex XIII, Para 1.3 based on evaluation of available data, and can be considered as “T” for the purposes of the assessment.

 

Conclusion

Although the substance can be considered to fulfil the criteria for Persistency and Toxicity, it does not fulfil the criteria for Bioaccumulation, as specified in REACH Annex XIII. As such, the substance cannot be considered as a PBT or vPvB substance, based on the available data.

 

PBT/vPvB criteria:             Not classified.