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Toxicity to microorganisms

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Description of key information

No study of toxicity to micro-organisms is available  for HMDTMP(4-7Na). A reliable study, performed with a Na/H salt of EDTMP, is available. The EC50 to WWTP micro-organisms was determined to be >100 mg active acid/L in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Key value for chemical safety assessment

EC50 for microorganisms:
100 mg/L

Additional information

In a study conducted with the sodium salt of EDTMP, according to OECD 209, 5.4% inhibition was seen at 100 mg/L loading (in terms of active acid), thus the EC50 is >100 mg active acid/L. No NOEC or EC5 was derived by the report authors, however in view of the low level of inhibition (approximately 5%) seen at a loading of 100 mg active acid/L, it is considered acceptable to interpret this concentration as an approximation of the EC5 for the purpose of PNEC derivation.

Both HMDTMP and EDTMP share a common chemistry incorporating alkyl backbones with one or more tertiary amine centres and multiple methylphosphonate groups present.


HMDTMP acid (CAS 23605-74-5) has two aminobismethylphosphonate groups, connected by a hexyl chain. EDTMP acid (CAS 1429-50-1) has two aminobismethylphosphonate groups, connected by an ethyl chain.


As well as being structural analogues, both phosphonates have consistent chemical properties including high MW (492 and 436 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 and potassium counterions of these phosphonates are not significant in respect of the properties under consideration and have been assessed in depth in the public literature. Additionally, the counterions are 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 analogue group and the validity of read-across are presented in the CSR Chapter 1.