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 soil

Administrative data

Endpoint:

biodegradation in soil: simulation testing

Type of information:

(Q)SAR

Remarks:

OASIS Catalogic Soil Simulator (v.03.09)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model, but not (completely) falling into its applicability domain, with adequate and reliable documentation / justification

Remarks:

Dihexyl dithiophosphate was in the parametric domain of the model and 94.12% in the structural domain (94.12% correct fragments; 5.88% unknown).

Applicant's summary and conclusion

Executive summary:

The OASIS Catalogic Soil Simulator (v.03.09) was used to model the transformation of dihexyl dithiophosphate to determine whether the same transformations will occur in media other than water/STP. As seen in the figure in the ‘illustration’ sections, transformation in soil is similar to STP in that the thio group is transformed to oxo and a minor pathway is also alkyl side chain oxidation and subsequent degradation (0.073 mol/mol parent, compared to 0.095 mol/mol parent predicted by Catalogic 301C). In soil, there is one pathway not predicted by Catalogic 301C: alkylphophinite hydrolysis. Unlike with Catalogic 301C, the alkyl side chain group is hydrolyzed on the parent molecule directly instead of first undergoing oxidative desulfuration. Oxidation of the sulfur group occurs after this transformation, ultimately leading to the same transformation products. A comparison of the metabolic maps from the soil simulator and 301C results in a similarity of the degradation products of 91.4% (see attached weight of evidence assessment in summary endpoint record for biodegradation screening in water). This is reasonable to expect as dihexyl dithiophosphate is a relatively simple molecule and microbial enzymatic activity is conserved among bacteria resulting in common degradation pathways. Therefore, the same transformation products are expected in water, soil, and sediment.