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PBT assessment

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PBT assessment: overall result

PBT status:
the substance is not PBT / vPvB

DBTO is not readily biodegradable according to a ready biodegradability study (OECD 301F, Hanstveit, R. (2003)) and therefore in the absence of any further data it can be concluded that DTBO fulfils the P-screening criteria

Although BCF values >5000 estimated with QSARs are available, these are not considered to be reliable for organometallic chemicals due to the fact that EPI Suite (the programme used to generate the prediction) is not validated for these types of materials for this endpoint. The program estimates BCFs of an organic compound using the log octanol-water partition coefficient (Kow). However, the log Kow estimation for the test material used to calculate the BCF was itself also determined in EPI Suite which is, again, not validated for organometallic substances with respect to this particular endpoint. As a result of this, the QSAR findings must be considered to be unreliable.

In the absence of any experimental data for dibutyltin oxide (DBTO), it is considered justifiable to read across from data on the similar compound dibutyltin dichloride (DBTC). In aquatic bioaccumulation studies, DBTC produced BCFs of 5 to 135; these values are significantly below 2000.

Therefore based on the fact that the known and readily available QSARs are not considered reliable for organometallic chemicals, it is suggested that the use of the read-across data is preferable. Consequently, DBTO can be considered not to satisfy the bioaccumulation criterion.

At the moment no chronic data are available, although a daphnia reproduction study is planned (see section 6.1.4). All the acute endpoints (EC/LC50s) are >0.1 mg/L. No NOEC was obtained in the algal study (also considered a long term end point); indications are that it is <0.2 mg/L, though the effects in this study were not considered to be dose related.

Therefore DBTO is not considered to satisfy the T criterion based on the aquatic environment.