Sodium salts of [hexane-1,6-diylbis[nitrilobis(methylene)]]tetrakisphosphonic acid (4-7 Na:1)

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes

Analytical monitoring:

no

Details on sampling:

not reported

Vehicle:

no

Details on test solutions:

no further information

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Inoculum source: Buckland sewage treatment works, Newton Abbot, Devon, UK (predominantly domestic sewage)
- Pretreatment: kept aerated and maintained at 20ºC
- Initial biomass concentration: suspended solids 5112 mg/L

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Post exposure observation period:

not reported

Hardness:

not reported

Test temperature:

20ºC

pH:

not reported

Dissolved oxygen:

not reported

Salinity:

not reported

Nominal and measured concentrations:

Nominal concentration: 100 mg/L as active acid.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

other: active acid

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

The % inhibition reported for this test substance after 3 h duration was 5.4%.

Results with reference substance (positive control):

- Result with reference substance was valid
- Relevant effect levels: EC50 19.5 mg reference substance/L

Reported statistics and error estimates:

not reported

Validity criteria fulfilled:

yes

Remarks:

The EC50 for the reference substance was in the expected range. The oxygen uptake in the blank control is not reported.

Conclusions:

The EC50 to WWTP micro-organisms was determined to be >100 mg/L as active acid, in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

No study of toxicity to micro-organisms is available  for HMDTMP(4-7Na). A reliable study, performed with the analogue substance, EDTMP-xNa, 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.

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 K_ow(≤-4 for both substances) and are highly soluble in water. The substances generally possess 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 read-across is presented in the Target EPSR and in a data summary in IUCLID Section 13.