Reaction mass of Octadec-9-en-1-yl ammonium di-n-hexyl phosphorodithioate and Octadec-9-en-1-yl ammonium mono- and di-butylphosphate

Biodegradation in water and sediment: simulation tests

Administrative data

Endpoint:

biodegradation in water: simulation testing on ultimate degradation in surface water

Type of information:

(Q)SAR

Remarks:

OASIS Catalogic 301C (v.12.17)

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Remarks:

This is a robust prediction as the substance was in the parametric domain, structural domain (100% fragments correctly predicted), and mechanistic domain (QPRF attached).

Applicant's summary and conclusion

Executive summary:

OASIS Catalogic 301C (v.12.17) was used to predict the transformation products of dihexyl dithiophosphate. An analog substance, sodium O,O-diethyl dithiophosphate (CAS 298-06-6) was found to biodegrade to ethanol, acetaldehyde and orthophosphate (Sherburn and Large, 1999; attached). This is consistent with the transformation observed in the Catalogic 301C model for CAS 298-06-6 (see illustration in attached weight of evidence document for biodegradation). The first step is oxidative desulfuration followed by sulfur-phosphorus bond cleavage resulting in a dialkyl phosphate ester. Phosphate ester hydrolysis then cleaves the alkyl chain producing an alcohol (in this case ethanol). Acetaldehyde is then produced from the subsequent biodegradation of ethanol.

 

A similar transformation occurs with dihexyl dithiophosphate per the Catalogic 301C model. As depicted in the figure in this endpoint study record (see QPRF for the complete pathway), the majority of the transformation will occur through the same pathway as for the sodium diethyl hydrogen dithiophosphate leading to phosphate ester hydrolysis and production of the alkyl alcohol. Analogs in the Catalogic 301C training set with metabolic maps supporting this pathway are found in Appendix 5 of the QPRF.  

 

There is another, minor, pathway predicted that results in oxidation and subsequent degradation of the alkyl chain (without phosphate ester hydrolysis; right side of Figure 9). The quantity predicted for this pathway (sum of all transformation products in the entire pathway) is 0.095 mol/mol parent.

 

The parent quantity predicted as remaining is 0.385 mol/mol parent. The most stable degradant predicted is the oxidative desulfuration product, which has the thio converted to an oxo, and is present at 0.517 mol/mol parent. Ultimately, transformation to the corresponding alkyl phosphate ester occurs, which is similar to starting material 2 (dibutyl phosphate).

 

Therefore, there is sufficient evidence to determine the transformation products of dihexyl dithiophosphate ester.