Reaction mass of 3-[3-(9-butyl-1,1,3,3,5,5,7,7,9,9-decamethylpentasiloxanyl)propoxy]-2-hydroxypropyl 2methylprop-2-enoate and 1-[3-(9-butyl-1,1,3,3,5,5,7,7,9,9-decamethylpentasiloxanyl)propoxy]-3-hydroxypropan-2-yl 2-methylprop-2-enoate

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

The substance is not a PBT substance as the Toxicity 'T' criteria is not met.

The substance is considered to be a vPvB substance, as although the substance may be considered as vP (based on available data), the substance is considered unlikely to meet the criteria for vB.

However, due to the identified persistence and bioaccumulation potentiual of the substance it will be handled and controled under conditions to minimise exposures and emissions to the environment.

Bioaccumulation:

A weight of evidence approach based on the following information has been made for the assessment of vB

-Estimated log Kow values:

The experimental log Kow was >6.5. A log Kow prediction using EPISUITE model KOWWIN (v 1.68) gives a predicted log Kow 11.19.

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. The aquatic BCF of a substance is probably lower than 2000 if the calculated log Kow is higher than 10. This may therefore indicate that based on the high log Kow of the substance, bioaccumulation may not be 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 estimated log Kow): BCF = 118 L/kg

- Arnot-Gobas BCF Method (assuming a biotranformation rate of zero): BCF = 6.382 L/kg

- Arnot-Gobos BCF Methods (including biotransformation rate estimates): BCF = 3.73 - 5.546 L/kg (range for upper trophic to lower trophic level)

These results of this model support the substance as not vB.

US EPA T.E.S.T model (v4.2.1 - nearest neighbour): BCF = 159.23 L/kg

VEGA (BCF models included):

-CAESAR (v2.1.14): BCF = 0.62 L/kg

-Meylan (v.1.0.3): BCF = 555 L/kg

-Arnot-Gobas (v1.0.0): BCF = 2006

It should be noted that the above models are not considered to be of high reliability due to models being outside the applicability domains, poor statistics and limited datasets in models. However, the BCF results available from these models would not support the substance as being vB.

-Chronic toxicity studies with mammals:

No chronic toxicity studies are available for the substance. However, a sub-acute oral (gavage) combined OECD 422 study 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 substances high log Kow does suggest an affinity to accumulate in fatty tissues, but this accumulation is expected to be limited by low absorption/uptake of the substance.

Summary:

The substance does have bioaccumulation potential based on available data and is considered to meet the B criteria (BCF >2000 L/kg) based on screening criteria (log Pow >4.5), Based on a weight of evidence assessment it is considered that the bioaccumulation potential of the substance is unlikely to meet the vB criteria.

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