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Description of key information

EC 434-280-4 dissociates immediately in contact with water to its starting materials:  


 



  1. (Z)-octadec-9-enylamine (CAS 112-90-3)

  2. Dibutyl hydrogen phosphate (CAS 107-66-4)

  3. Butyl dihydrogen phosphate (CAS 1623-15-0)

  4. O,O-dihexyl hydrogen dithiophosphate (CAS 78-64-8; AKA Di-n-hexyl dithiophosphoric acid)


 


Therefore, it is technically not feasible to conduct simulation studies, as these are not designed to assess complex mixtures. Instead, the (bio)degradation potential of each is relevant to assess the potential persistence of EC 434-280-4.


 


The existing OECD 301F biodegradation study with EC 434-280-4 resulted in 0% degradation after 28-days. However, this study has little applicability to the overall weight of evidence as, per the study report, the test material was described as “an insoluble, sticky, viscous liquid” and because of this the test material was dispensed onto a glass filter paper prior to addition to the test vessels. This may have prevented dissociation and further solubilization of the dissociation products of EC 434-280-4. This is consistent with the behavior of (Z)-octadec-9-enylamine to sorb to glass. In the Committee for Risk Assessment Annex 1 Background document on (Z)-octadec-9-enylamine (2011; attached) it states in regard to biodegradation that “The prolonged lag phase may be attributed to the high sorption tendency of long-chain alkyl amines to glass surfaces or organic matter, leading to a reduced bioavailability” (page 17).


 


There is sufficient data and information to conclude that (Z)-octadec-9-enylamine and both constituents of butyl acid phosphate (dibutyl phosphate and butyl dihydrogen phosphate) are not persistent in the environment based on existing readily biodegradation studies. A weight of evidence evaluation is conducted for dibutyl phosphate to support this conclusion (see attached document). This weight of evidence includes data from larger molecular weight analogs (tributyl phosphate (CAS 126-73-8); bis(2-ethylhexyl) hydrogen phosphate (CAS 298-07-7)) that are readily biodegradable as well the data available for dibutyl phosphate itself.  


 


Regarding, dihexyl dithiophosphate, this substance meets the persistence screening criteria as it is not expected to be readily biodegradable based on OASIS Catalogic 301C modeling and analog data. However, there is reliable and adequate information on the transformation products of dihexyl dithiophosphate, satisfying the need for simulation studies to identify the transformation products. This includes OASIS Catalogic 301C predictions, which is supported by published literature on the transformation of dialkyl dithiophosphates (see attached assessment for the details and references).


 


The weight of evidence assessment of the biodegradation potential is found in the ‘Biodegradation in water screening tests’ section (summary endpoint), as this assesses the biodegradation potential of the four starting materials. Regarding the simulation studies in water, sediment, and soil, the OASIS Catalogic data for the transformation of dihexyl dithiophosphate is provided, only, as the remaining three starting materials do not meet the persistence screening criteria and are, therefore, not relevant for simulation studies. Endpoint study records for the water simulation study and soil simulation study contain this information and the QPRFs. 

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