Dibutyltin oxide

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation in aquatic species: fish

Data waiving:

study technically not feasible

Justification for data waiving:

other:

Description of key information

This study was waived on the basis that it was not technically feasible to conduct.

Additional information

Following decision number CCH-D-0000003196-74-05/F, it was attempted to conduct the bioaccumulation in aquatic species study (OECD 305) required under point 9.3.2. of Annex IX of Regulation (EC) No. 1907/2006. It was determined however that it is not technically feasible to conduct this study, due to the inability to develop a substance specific analytical method that could be used to monitor the substance during the performance of the test.

 

DBTO does not exist as (CH3CH2CH2CH2)2-SnO, but rather as a polymeric species of tin and oxygen linkages. There is no exact molecular weight or fixed structure. The polymer is insoluble in virtually all common solvents. Initially an evaluation to determine the solubility of DBTO in methanol, water, acetonitrile, isopropylalcohol, dimethylformaldehyde and acetone was attempted. In each of the solutions none of the DBTO visibly dissolved even after sonification. Following this further solvents were then used, tetrahydrofuran, acidified water, dichloromethane, hexane, diethyl ether, petroleum ether, isooctane, toluene, ethyl acetate, dimethyl sulfoxide and 50 % hydrochloric acid in water, but again no solubility was observed. It can therefore be concluded DBTO was completely insoluble in all solvents tested.

 

A very thorough attempt was made to develop methodology for the quantification of the registered material (DBTO) and its organic acid salt in aqueous and tissue matrices. The following techniques were tried.

 

- Attempted Chromatography of DBTO by GCMS/EI

A literature search indicated that DBTO is transformed in weak, organic acids. In a weak organic acid like formic acid, DBTO is transformed to the tin diformate salt. The acid solution was diluted with methanol and a scan was run on GCMS with electron impact (E.I.) against an acid/methanol blank. The two chromatograms were identical. The solutions were scanned on a UV/VIS spectrophotometer in hopes that the transformation produced some absorption in the low UV range. The absorption of formic acid was all that was noted. The solutions were analysed by high performance liquid chromatography (HPLC) with UV detection using a simple gradient of acetonitrile and 0.1 % phosphoric acid. No peaks in the fortified sample were observed that were not present in the blank sample.

 

- Attempted Chromatography of DBTO by GCMS/CI

This procedure was repeated with acetic acid with GCMS/EI scans, UV/VIS scans and HPLC analyses. No analyte was detected in any analyses. In hopes of producing a CI active derivative, the procedures were repeated with trifluoroacetic acid. By producing the di-(trifluoroacetyl) derivative, it was hoped to impart mass spectrometry CI activity. The samples were reacted with trifluoroacetic acid, dissolved in hexane and analysed by GCMS/CI and GCMS/EI. No derivatives were detected.

 

- Attempted Chromatography of DBTO Derivative by HPLC/UV

DBTO (having polymeric characteristics) could not be solubilised and therefore could not be analysed by traditional methods. The chance of forming an ion pair with a UV absorbing chromophore that could be analysed by HPLC was evaluated with the hope that if a diaromatic tin complex by reaction with an acid could be formed it, might elute from a short HPLC column. A methanolic stock of benzoic acid was prepared and DBTO was added. A concurrent blank was analysed with the degraded sample by gradient elution, reverse phase HPLC at 220 nm. No difference in the fortified sample and the blank was noted. Various wavelengths were attempted with no success.

 

In conclusion it was not possible to analyse the substance using GCMS/EI, GCMS/CI or HPLC/UV. DBTO cannot be analysed by gas chromatography and although many polymers can be analysed by high performance liquid chromatography, this species will not absorb UV light, fluoresce or be detected by other traditional methods. Refractive index and ELSD detectors will not afford the sensitivity required for soil and aquatic toxicity testing. DBTO can be transformed into its diacid tin salt, but this solution cannot be analysed by GCMS due to lack of volatility. Similarly, the diacid salt cannot be analysed by HPLC due to a lack of a chromophore. It was therefore not possible develop a substance specific analytical method that could be used to monitor the substance during the performance of the test and as such the study is determined not to be technically feasible to conduct.

 

Additional information:

 

A literature search was conducted in order to determine the available data on the registered substance. No appropriate data that was judged to be both reliable and relevant to the material itself was uncovered. 

It should also be noted that although BCF values in excess of 5000 estimated with QSARs are available, these are not considered to be reliable. This is due to the fact that EPI Suite (the programme used to generate the prediction) is not validated for these types of materials (organometallic chemicals) for this endpoint. The program estimates BCFs of an organic compound using the log octanol-water partition coefficient (Kow). However, the log Kow estimation 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 are not considered to be unreliable.