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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

No standard guideline screening studies of biodegradation in fresh water are available for BHMT acid or its salts. A screening biodegradation study in seawater in accordance with OECD 306 is available which shows very low levels of biodegradation. Together with evidence of very low biodegradability from standard tests with other aminomethylenephosphonates, this gives weight of evidence for low levels of biodegradability.

Key value for chemical safety assessment

Additional information

The registration substance is part of a category family (super-category; see CSR for more details) which consists of several phosphonates that share a common chemistry incorporating alkyl backbones with one or more tertiary amine centres and multiple methylphosphonate groups present.

 

HMDTMP-H (CAS 23605-74-5) has two aminobismethylphosphonate groups, connected by a hexyl chain. BHMT acid (CAS 34690-00-1) has three amine centres (five methylphosphonate groups), connected by hexyl chains.

 

As well as being structural analogues, both phosphonates have consistent chemical properties including high MW (492 and 685 respectively), very low log Kow(≤-4 for both substances) and are highly soluble in water. The substances generally posses similar physico-chemical properties and are not readily biodegradable.

 

The sodium counterion of HMDTMP-xNa is not significant in respect of the properties under consideration and has been assessed in depth in the public literature. Additionally, the counterion is expected to dissociate when in contact with water, including atmospheric moisture.

Therefore, for the purpose of this assessment, read-across is considered valid. Further information on the super-category and the validity of read-across are presented in the CSR Chapter 1.