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Reference
Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
21 September 2016 to 07 November 2017
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Objective of study:
other: hydrolysis is a function of pH
Qualifier:
according to guideline
Guideline:
other: OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
no
Radiolabelling:
not specified

HYDROLYSIS AT PH 4, 7 AND 9

- The unhydrolysed test material was characterised by a single signal at 76 ppm. Although the test material is composed of two constituents, the difference in the alkylchains of the ligands does not influence the chemical shift of the central tin-atom.

- At pH 4 and 7 the 119Sn-NMR spectra was not different compared to the unhydrolised test material.

- The pH 9 spectrum of the extracted hydrolysate showed a significant decrease of the product peak at 76 ppm (10 Mol%) and the appearance of a sharp peak at -45 ppm (90Mol%)

- -45 ppm is a characteristic chemical shift for DOTTG, which can be formed by initial hydrolysis of one ligand and as a subsequent nucleophilic attack of the ester function of the second thioglycolate ligand leading to a ring closure to DOTTG.

HYDROLYSIS AT PH 1.2

- The 119Sn-NMR spectrum of the organic extract the substance signal decreased to 27 Mol% in intensity.

- An additional broad peak appeared at 32 ppm (72 Mol%).

- The new peak can be attributed to the dioctyltin chloro lauryl-myristyl thioglycolate (DOTC-LMTG) the monochloroester of the test material. This hydrolytical behaviour is well known from other dialkyltin thioglycolates.

- No DOTC was formed under the conditions of the study

MASS BALANCE RECOVERY RATES

pH 4: 99 %

pH 7: 98 %

pH 9: 91 %

pH 1.2: 98 %

ATOMIC ABSORPTION SPECTOMETRY

- The aqueous phase of the low pH hydrolysis has been analysed after extraction with hexane by AAS and contained < 5mg/L Sn. So the formation of an organotin substance better soluble in water than in hexane can be excluded.

Conclusions:
The test material can be considered hydrolytically stable at pH 4 and 7. After 5 days of hydrolysis at 50 °C at pH 4 and 7 no reaction could be identified based on the 119Sn NMR spectra of the extracted hydrolysates.
At pH 9 under the same conditions DOTTG was formed as the only breakdown product.
Under simulated gastric conditions the test material was found to break down to its monochloroester,dioctyltin chloro laurylmyritylthioglycolate.
The formation of DOTC can be excluded.
The tin content in the aqueous phase of the hydrolysis remained under the detection limit of < 5 mg/L in AAS, thus the formation of a water soluble organotin species can be excluded.
Executive summary:

The hydrolysis of the test material as a function of pH was investigated in accordance with the standardised guidelines OECD 111 and EU Method C.7.

The stability of the test material was investigated at pH 4, 7 and 9 and pH 1.2 using NMR spectroscopy.

Under the conditions of the study, the test material was considered to be hydrolytically stable at pH 4 and 7. After 5 days of hydrolysis at 50 °C at pH 4 and 7 no reaction could be identified based on the 119Sn NMR spectra of the extracted hydrolysates.

At pH 9 under the same conditions DOTTG formed and was the only breakdown product.

Under simulated gastric conditions the test material was found to break down to its monochloroester, dioctyltin chloro laurylmyritylthioglycolate.

The formation of DOTC can be excluded.

The tin content in the aqueous phase of the hydrolysis remained under the detection limit of < 5 mg/L in AAS, thus the formation of a water soluble organotin species can be excluded.

Description of key information

Hydrolysis as a Function of pH

The test material can be considered hydrolytically stable at pH 4 and 7. After 5 days of hydrolysis at 50 °C at pH 4 and 7 no reaction could be identified based on the 119Sn NMR spectra of the extracted hydrolysates.

At pH 9 under the same conditions DOTTG was formed as the only breakdown product.

Under simulated gastric conditions the test material was found to break down to its monochloroester,dioctyltin chloro laurylmyritylthioglycolate.

The formation of DOTC can be excluded.

The tin content in the aqueous phase of the hydrolysis remained under the detection limit of < 5 mg/L in AAS, thus the formation of a water soluble organotin species can be excluded.

Key value for chemical safety assessment

Additional information

Hydrolysis as a Function of pH

The hydrolysis of the test material as a function of pH was investigated in accordance with the standardised guidelines OECD 111 and EU Method C.7.

The stability of the test material was investigated at pH 4, 7 and 9 and pH 1.2 using NMR spectroscopy.

Under the conditions of the study, the test material was considered to be hydrolytically stable at pH 4 and 7. After 5 days of hydrolysis at 50 °C at pH 4 and 7 no reaction could be identified based on the 119Sn NMR spectra of the extracted hydrolysates.

At pH 9 under the same conditions DOTTG formed and was the only breakdown product.

Under simulated gastric conditions the test material was found to break down to its monochloroester, dioctyltin chloro laurylmyritylthioglycolate.

The formation of DOTC can be excluded.

The tin content in the aqueous phase of the hydrolysis remained under the detection limit of < 5 mg/L in AAS, thus the formation of a water soluble organotin species can be excluded.