tetrakis(2,6-dimethylphenyl)-m-phenylene biphosphate

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

The substance displays a low ready biodegradability in that it achieved 13.23% biodegradation in a 28-day study, indicating that it is unlikely to achieve a half-life of less than 40 or 60 days within fresh water attributed to ready biodegradation alone.

The hydrolysis of the substance has not been assessed by testing due to the limitations of the study method with insoluble substances. Furthermore, studies on direct photo transformation in water are not available but it is assumed on the basis of chemical structure that the substance is not degraded by hydrolysis or direct photolysis.

The substance is considered to be persistent in the environment were exposure to occur based on the known lack of ready biodegradation and a perceived likelihood that abiotic processes would not contribute significantly to the depletion of the substance within the environment.

The partition coefficient of the substance was measured to be >6.2 by means of the HPLC method. The limit value is due to the limitation of the method. It was therefore considered appropriate to undertake an estimation of the partition coefficient by means of QSAR estimation based upon the SMILES code of the molecule using US EPA KOWWIN v1.67 of the EPI Suite v4. Based upon structural fragmentation drawn from a database of >40,000 substances, including aryl phosphate esters and aromatic species predicted for the fragmentation estimates, the log Pow is estimated to be 11.79.

Based on these data, the substance may be considered to be of concern as potential for bioaccumulation, according to screening criteria for bioaccumulation in ECHA guidance (Chapter R.11 PBT Assessment). The likely reliability of the log Pow is, however, considered to diminish above a value of 6, as noted in Appendix R.11-1 Annex 1 of ECHA guidance on PBT Assessment. Substances with log Pow between 4.5 and 6 are considered likely to be highly accumulating; however no substantial bioconcentration is assumed for compounds having log Pow with values less than 4.5 or greater than 6. For compounds having log Pow greater than 6, a gradual decrease of the BCF is observed and it has been hypothesised within the published literature that a high log Pow is more an effect of solubility than a tendency of the substance to be lipophilic.

Considering that the measured log Pow is a limit value at 6.2 and has been estimated based on structure to be 11.79, the results indicate that the substance is likely to be non-bioaccumulating based on the partition coefficient.

Acute toxicity studies:

No acute toxicity recorded up to levels of water solubility (LC50/EC50 values therefore not identified and studies concluded as limit tests).

Chronic Toxicity studies:

Chronic toxicity studies in daphnia available for the substance itself and a related aryl phosphate substance both showed an absence of chronic toxicity effects at the solubility limit and chronic toxicity NOEC values were determined to be greater than the water solubility limit.

Sediment organism studies:

The sediment organism study data available by read across on a representative and related aryl phosphate show no toxicity to Chironomus riparius or Lumbriculus variegatus achieving the EC50 and NOEC values as limit values greater than the maximum required dose for the test guideline.

Soil macro-organisms study:

The earthworm toxicity study available by read across on a representative and related aryl phosphate showed no toxicity to earthworms, achieving the EC50 and NOEC values as limit values greater than the maximum required dose for the test guideline.

Soil micro-organisms:

The nitrogen transformation study available by read across on a representative and related aryl phosphate showed no inhibition of the nitrate formation rate, achieving the EC50 and NOEC values as limit values greater than the maximum required dose for the test guideline.

Toxicity to terrestrial plants:

The terrestrial plant toxicity study data available by read across on a representative and related aryl phosphate show no inhibition to growth of the soybean, tomato and oat seedlings achieving the EC50 and NOEC values as limit values greater than the maximum required dose for the test guideline.

Mammalian toxicity

The submission substance was found to be non-toxic by both the oral and dermal routes of exposure duing OECD Guideline studies. A study to determine the inhalation toxicity of the substance has not been conducted due to it being considered scientifically unjustified.

The submission substance was found to be neither toxic nor harmful by the oral route of exposure during a 28-day repeat dose toxicity study.

Repeat dose studies via the dermal and inhalation routes of exposure were not conducted on the basis of a lack of exposure to the submission substance.

Likely routes of exposure:

The substance is a white powder of a particle size that is not breathable and is generally used in closed conditions until formulated into product.

The likely route of exposure to workers would be by dermal exposure.