3-[3-(1,1,1,3,5,5,5-heptamethyltrisiloxan-3-yl)propoxy]- 2-hydroxypropyl methacrylate and 1-[3-(1,1,1,3,5,5,5-heptamethyltrisiloxan-3-yl)propoxy]-3-hydroxypropan-2-yl methacrylate

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

The substance is not considered to be a PBT, as the Toxicity 'T' criteria is not met.

The substance is not considered to be a vPvB, as the although the substance can be considered P/vP and B, a weight of evidence assessment indicates bioaccumulation is unlikely to be sufficient to meet the vB criteria (see details on bioaccumulation below).

However, due the identified persistence and bioaccumuation potential of the substance the substance will be handled and controlled as if it was a PBT/vBvP e.g. conditions of use to minimise exposures and emissions to humans and the environment.

Bioaccumulation:

Based on the log Kow screening criteria the substance meets the criteria for B as log Kow >4.5. The assumption behind this is that the uptake of an organic substance in aquatic organisms is driven by its hydrophobicity.

The screening criteria is not sufficient for concluding on whether the substance also meets the vB criteria. No bioaccumulation study (in aquatic species) is available, so a weight of evidence approach based on the following information has been made for the assessment of vB.

- Estimated log Kow values:

Experimental log Kow was >6.5. log Kow prediction was made using EPISUITE model KOWWIN (v1.68) and gave predicted log Kow of 6.81.

At log Kow values between 4 and 5, Log BCF increases linearly with log Kow, if the substance is absorbed at the same rate and if it is not biotransformed.   This linear relationship is the basis for the B screening threshold value of log Kow > 4.5. However, at very high log Kow (>6), a decreasing relationship between the two parameters is observed. This may therefore indicate that based on the high log Kow of the substance, bioaccumulation may not sufficient to meet the vB crieria (aquatic BCF >5000 L/kg).

- Estimated BCF values:

A number of models have been run to estimate aquatic BCF results for the substance:

EPISUITE model BCFBAF (v3.01): This model provides a number of results:-

- Regression-based estimated (based on log Kow): BCF = 14400 L/kg

- Arnot-Gobas BCF Method (assuming a biotranformation rate of zero): BCF = 14630 L/kg

- Arnot-Gobos BCF Methods (including biotransformation rate estimates): BCF = 876 - 1337 L/kg (range for upper trophic to lower trophic level)

These results of this model (assuming no biotransformation) support the substance as vB.

US EPA T.E.S.T model: BCF = 159 L/kg

OECD Toolbox: BCF = 43 L/kg

VEGA (3 BCF models included):-

-CAESAR (2.1.14): BCF = 24 L/kg

-Meylan (1.0.3): BCF = 290 L/kg

-KNN (1.1.0): BCF = 3.3 L/kg

It should be noted that the above models are not considered to be of high reliability due to some models being outside the applicability domain, poor statistics and limited datasets in models. However, as a weight of evidence the BCF results from these models would not support the substance as being vB or even B.

Octanol solubility:

The substance has been found to be highy soluble in octanol. Based on the results of a preminlary test, the octanol solubility can be given as >1000 g/L at room temperature.

Octanol is often used as a surrogate for fish lipids but the solubility in n-octanol is not a parameter that is directly related to the BCF value. Octanol solubility is only an indicator for substances accumulating in fatty tissues and certain substances may bind to proteins instead of partition into lipids.

Therefore, on its own the high solubility of the substance in octanol does not provide conclusive evidence that the substance would meet the vB criteria (BCF >5000 L/kg).

Chronic toxicity studies with mammals:

No chronic toxicity studies are available for the substance. However, a sub-acute oral (gavage) combined OECD 422 study (conducted on a structurally similar analogue substance) did not show any adverse systemic toxicity effects of treatment at 1000 mg/kg bw/day (highest dose level). This gives some indication that the substance is non-toxic and/or that it is not taken up to a significant extent.

Toxicokinetics:

A toxicokinetic assessment of the substance concluded that there was limited evidence of absorption/uptake of the substance via the oral and dermal routes based on the available data. Uptake of the substance after exposure is therefore expected to be low. The substance high log Pow does suggest an affinity to accumulate in fatty tissues, but this accumulation is expected to be limited by low absorption/uptake of the substance.

Conclusion: The substance does have bioaccumulation potential and based on the available data is considered to meet the B criteria (BCF >2000 L/kg). Based on a weight of evidence assessment it is considered that the bioaccumualtion potential of the substance is unlikely to be sufficient to meet the vB criteria (BCF >5000 L/kg).