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Environmental fate & pathways

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In the biodegradation in water screening test, the test material was found to inhibit the degradation of the reference substance and also inhibited the oxygen consumption in the biodegradability test. From the available data it was not possible to accurately draw conclusions, as any potential biodegradation of tributylchlorostannane would have been masked by its inhibiting effect on the inoculum, howerver, the test material is not toxic according to the definitions given by the guidelines.

From the two available studies on biodegradation screening in water and sediment, biodegradation of TBT to DBT and MBT was noted in both studies in water. A difference was noted between the effectiveness of the different bacterial cultures in Errécalde et al (1995), where some appeared to be more effective than others in degrading TBT. In Adelman et al (1990), it was noted that there was no noticeable degradation of TBTC in the sediment. Although Errécalde et al (1995) stated that all seven microorganisms utilised in the study possessed the ability to metabolise TBTCl to various extents ranging from 6 to 32 %. However, partitioning of the substrate remaining at the end of the reaction, and the resulting metabolites (DBT and MBT), between the solution and the biomass was found to vary considerably in relation to the nature of the organotin and the microorganism present. For fungi, TBT and DBT were mainly recovered from the biomass, whereas MBT was mostly in solution. For yeasts and bacteria, there was no apparent trend, except that MBT was recovered almost exclusively from solution. It was not determined whether the organotins associated with the biomass were adsorbed on the external part of the cells or included within them. A likely hypothesis behind the partition of butyltins between solution and biomass is in some way dependent on their relative hydrophobic characteristics (cf. the large proportion of monobutyltin in solution).