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Environmental fate & pathways

Biodegradation in water: screening tests

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biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to the appropriate OECD test guideline, and in compliance with GLP.
according to guideline
OECD Guideline 301 E (Ready biodegradability: Modified OECD Screening Test)
GLP compliance:
Oxygen conditions:
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
Activated sludge from the HRC sewage treatment plant. The nature of the influent to this treatment plant is not known.

The activated sludge was filtered through Whatman No 1 paper (first 200 ml discarded) and the filtrate was kept aerated until used. 
Duration of test (contact time):
28 d
Initial conc.:
40 other: mg C/l
Based on:
Parameter followed for biodegradation estimation:
other: dissolved organic carbon removal
Reference substance:
other: sodium benzoate
% degradation (DOC removal)
Sampling time:
28 d
Details on results:
Briquest 462-25S attained 0% degradation after 28 days and
was not considered readily biodegradable under OECD
Guideline No. 301-E. The control substance attained 85%
degradation after 14 days and 97% after 28 days, confirming
suitability of the inoculum and culture conditions.

Degradation products: no
Results with reference substance:
Day 7: 79%
Day 14: 85%
Day 28: 97%
Validity criteria fulfilled:
Interpretation of results:
under test conditions no biodegradation observed

Description of key information

No study of ready biodegradation of potassium salts of HMDTMP are available. 0% removal (based on DOC removal) was observed in a reliable study conducted using an analogous sodium salt of HMDTMP.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

This result is supported by findings in a further reliable test of ready biodegradability, showing extremely low levels of biodegradation of HMDTMP-H over 28 days (Martienssen, 2010.

Two studies of inherent biodegradation are also available for HMDTMP-H. Both show significant but highly variable levels of removal over the test period, probably due to adsorption combined with slow abiotic and biotic degradation mechanisms.

The acid, sodium and potassium salts in the HMDTMP category are freely soluble in water. The HMDTMP anion can be considered fully dissociated from its sodium or potassium cations when in dilute solution. Under any given conditions, the degree of ionisation of the HMDTMP species is determined by the pH of the solution. At a specific pH, the degree of ionisation is the same regardless of whether the starting material was HMDTMP-H, HMDTMP.4Na, HMDTMP.7K or another salt of HMDTMP.

Therefore, when a salt of HMDTMP is introduced into test media or the environment, the following is present (separately):

1. HMDTMP is present as HMDTMP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the media and not whether HMDTMP (4-7K) salt, HMDTMP (4-7Na) salt, HMDTMP-H (acid form), or another salt was used for dosing. At pH 5.5 - 6, the HMDTMP anions would be present on average as the HMDTMP trivalent anion according to the pH curves.  At neutral pH (7), the HMDTMP anions would be present on average as the HMDTMP pentavalent anion according to the pH curves. At pH 8, the HMDTMP anions would be present on average as the HMDTMP hexavalent anion according to the pH curves.

2. Disassociated potassium or sodium cations. The amount of potassium or sodium present depends on which salt was added.

3. It should also be noted that divalent and trivalent cations would preferentially replace the sodium or potassium ions. These would include calcium (Ca2+), magnesium (Mg2+) and iron (Fe3+). These cations are more strongly bound by HMDTMP than potassium and sodium. This could result in HMDTMP-dication (e.g. HMDTMP-Ca, HMDTMP-Mg) and HMDTMP-trication (e.g. HMDTMP-Fe) complexes being present in solution.