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IN VITRO GENE MUTATION STUDY IN BACTERIA

Ogorek. B (1992) a study performed to the OECD guideline 471 on a 65% pure sample of the test material was included as the key study for this data requirement. It has been conducted with generally accepted scientific principles, possibly with incomplete reporting or methodological deficiencies, which do not affect the quality of the relevant results, accordingly the study was assigned a reliability score of 2 in criteria with Klimisch (1997). The results with a Confirmatory Assay indicate that under the conditions of this study, in both initial and confirmatory assays, the test article, did not cause a positive increase in the numbers of revertants per plate of any of the tester strains either in the presence or absence of microsomal enzymes prepared from induced rat liver (S9).

IN VITRO CYTOGENICITY STUDY IN MAMMALIAN CELLS OR IN VITRO MICRONUCLEUS STUDY

 

Reimann R & Gramlich U (1990) was provided as the key study for this data requirement. The study was performed in compliance with GLP and the method was comparable to that of OECD 473. The study was accordingly assigned a reliability score of 2 and considered reliable and adequate for assessment. An evaluation of the clastogenic potential in the human lymphocyte test indicated clastogenic potential of the test material in the human lymphocyte test in vitro at clearly cytotoxic concentrations. From the four assays conducted without and with an extrinsic metabolizing system in two independent studies, one assay without and one with S9 mix gave statistically significant (P < 0.05) increases in the frequency of chromosomal aberrations at the highest concentrations evaluated, whereby in the remaining assays the results were borderline negative. In each assay of this investigation, the test material was tested up to cytotoxic concentrations as indicated by an obvious reduction of the mitotic index.

 

The CHO gene mutation study from the publication by Li AP et al (1982) was provided as a supporting study to this endpoint. The study was conducted to good scientific principles (GLP status was not reported), however the study did not include metabolic activation. The study was accordingly assigned a reliability score of 2. The LC50 value of DBTC for CHO cells, as determined by cloning efficiency, was approximately 0.35 µg/ml (1.12 µM). DBTC induced mutations at the HGPRT gene locus in CHO cells. The mutant frequency increased with dose up to 0.2 µg/ml (0.66 µM) for DBTC. A decrease in mutant frequency was observed at higher concentrations.

 

IN VITROGENE MUTATION STUDY IN MAMMALIAN CELLS

 

Lang R & Schmitt R (1989) was provided as the key study for this data requirement. The study was well documented, performed in compliance with GLP and to a method comparable to OECD 476. The study was assigned a reliability score of 2 and considered reliable and adequate for use. The study was a HGPRT-test with V79 cells. The test material was found to have cytotoxic effects without metabolic activation by S9 mix at 0.00006 µl/ml and with metabolic activation a clear toxic effect could be observed at 0.0003 µl/ml in the first experiment and at 0.0005 µl/ml in the second assay of the second experiment. The test material did not show a mutagenic potential in the HGPRT/V79 mammalian cell gene mutation test neither in the absence nor in the presence of rat liver S9 mix in two independently performed experiments.

 

IN VIVO MUTAGENICITY

 

Dance C (1991) was provided as the key study for this data requirement. The study was performed in compliance with GLP and according to the guideline OECD 474 (and EU Method B.12). The study was therefore assigned a reliability score of 1 and considered reliable and adequate for assessment. The study investigated the clastogenic action on bone marrow erythrocytes in a micronucleus. The test material showed evidence of induced chromosomal or other damage leading to micronucleus formation in polychromatic erythrocytes of mice treated orally with DBTC at 50 mg/kg and sacrificed 48 or 72 hours later. A biologically and statistically significant increase in the incidence of micronucleated polychromatic cells was observed in the bone marrow of mice treated with DBTC at 50 mg/kg and killed 48 and 72 hours later (0.01<p<0.05): this effect was seen more clearly in females than in males. No such effect was apparent for any group treated with DBTC and killed 24 hours later (p>0.05). Statistically significant increases over controls were also seen in positive control group animals given chlorambucil at 30 mg/kg (p<0.01).

 

A further in vivo mutagenicity study, (Lang R & Wedel JV (1990) was provided as supporting information. The GLP status of the study was not reported and no guidelines were listed. The study was performed to a good scientific standard with a good level of reporting of the methodology and the results. The study investigated the mutagenic potential of the test material in the mouse micronucleus test. The test material failed to show any evidence of mutagenic potential, when administered by gavage up to the toxic dose level of 200 mg/kg in the mouse micronucleus test. Triaziquone, the positive reference, gave the expected mutagenic response. After application of the high dose four males and one female died; after application of the mid dose, one male died. More than half of the animals of the two highest dose groups showed signs of toxicity (e.g. apathy, eyelid closure, ruffled fur).

 

OTHER:

In the second part to the Li AP et al (1982) study, a test was performed to determine the cytotoxicity of the test material to rat lymphocytes. The test is not a standard endpoint and was therefore provided for information purposes only. The study was performed to a good scientific standard with a good level of reporting. The LC50 for lymphocytes as determined by dye-exclusion was approximately 50 µg/ml (0.16 mM). At the same concentration of DBTC, the number of antibody-forming cells (AFC) was reduced to approximately 10 % of the control.

Overall summary:

The SPCFC (2004) review of organotins concluded that (organotins in general) did not exhibit any significant genotoxic potential in vivo, and that carcinogenicity seen with some organotin compounds was likely attributable to hormonal or immunotoxic actions. Dibutyltin salts are recommended for classification as mutagenic (R68) within the EU classification system. The available data for dibutyltin oxide and dibutyltin chloride as described above are inadequate to challenge that recommendation.



Short description of key information:
The following studies were submitted as key studies to address the genetic toxicity of the substance:

Ogorek. B (1992). Bacterial Mutagenicity Screening Test. Testing Laboratory: Genetiec Toxicity, CIBA-GEIGY Limited, CH-4002, Basle, Switzerland. Report Number: 924151. Owner Company: Additives Division, CIBA-GEIGY Limited, CH-4002, Basle, Switzerland. Report Date: 1992-11-05

IN VITRO CYTOGENICITY STUDY IN MAMMALIAN CELLS OR IN VITRO MICRONUCLEUS STUDY

Reimann R & Gramlich U (1990). ZK 22.663: Evaluation of the clastogenic potential in the human lymphocyte test. Testing laboratory: Schering AG, Pharmaceutical Research, Bergkamen, Germany. Owner company: Schering AG, Pharmaceutical Research, Bergkamen, Germany. Report No.: IC 1/90. Report Date: 1990-09-17.

IN VITRO GENE MUTATION STUDY IN MAMMALIAN CELLS

Lang R & Schmitt R (1989). ZK 22.663: Evaluation of gene mutations in mammalian cells in culture: HGPRT-test with V79 cells. Testing laboratory: Schering AG, Pharmaceutical Research, Bergkamen, Germany. Owner company: Schering AG, Pharmaceutical Research, Bergkamen, Germany. Report No.: IC 16/89. Report date: 1989-03-30.

IN VIVO MUTAGENICITY

Dance C (1991). Dibutyl tin chloride: assessment of clastogenic action on bone marrow erythrocytes in the micronucleus test. Testing Laboratory: Life Sciences Research Limited, Eye, Suffolk, IP23 7PX, England. Owner company: Atochem North America Incorporated, 900 first Avenue, P.O. Box C, King of Prussia, Pennsylvania, 19406-0018, USA. Report No.: 91/0357. Report date: 1991-11-08

With the exception of Ogorek (assigned a reliability score of 2 and performed on dibutyltin oxide), all the above listed studies were read-across from dibutyltin dichloride (a similar organotin compound) to the substance in question and assigned a reliability score of 2.

Endpoint Conclusion: Adverse effect observed (positive)

Justification for classification or non-classification

According to directive 67/548/EEC the substance is assigned the classification Mutagenicity category 3 and labelled with R68 – possible risk of irreversible effects. According to Regulation (EC) no 1272/2008 the test substance would be classified as Muta. 2 with the Hazard statement: H341: Suspected of causing genetic defects and should be accompanied with the signal word 'Warning'.