Tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate

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

Study period:

11/2008

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Origin: aeration tank of a domestic sewage treatment plant (Municipal STP Cologne-Stammheim)

Laboratory culture:Date of collection: 2008-11-24

Microbial inoculum:
- first, the sludge was settled and the supernatant was decanted
- after centrifuging (15 min at 4000 rpm and 20°C) the supernatant was decanted
- approx. 1 g of the wet sludge was dried in order to calculate the amount of wet sludge to achieve a concentration of activated sludge of 3 g/L (dry weight) suspended solids
- the calculated amount of sludge was first dissolved in synthetic medium and than filled up to a defined end volume with deionised water - before start of the test 10 mL of the sludge suspension were sucked of and the dry weight was controlled again. The sludge suspension was diluted with water to obtain a concentration of activated sludge of 2 g/L (dry weight) suspended solids

Storage of sludge: aeration of the activated sludge at 20°C ± 2°C, daily fed with synthetic medium

pH of the suspension before application: 7.7

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

Test item: 18.5 - 18.7 °C

pH:

Test item: 8.0 - 8.1

Dissolved oxygen:

Start: 6.2 - 6.4 mg O2/L
End: 2.8 - 3.7 mg/L

Nominal and measured concentrations:

Nominal: 10; 100; 1000 mg/L

Reference substance (positive control):

yes

Remarks:

3.5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 504 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: The 50.4% aqueous solution of 2-phosphonatobutane-1,2,4-tricarboxylate acid showed 4.3 % respiration inhibition of activated sludge at the highest test item concentration of 1000 mg/L corresponding to a concentration of 504 mg/L of PBTC

Key result

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 504 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: The 50.4% aqueous solution of 2-phosphonatobutane-1,2,4-tricarboxylate acid showed 4.3 % respiration inhibition of activated sludge at the highest test item concentration of 1000 mg/L corresponding to a concentration of 504 mg/L of PBTC

Results with reference substance (positive control):

The results with 3.5-Dichlorophenol:
15% inhibition and 18.0 mg/L*h at a concentration of 5 mg/L.
59.1% inhibition and 8.7 mg/L*h at a concentration of 10 mg/L.
83.8% inhibition and 3.4 mg/L*h at a concentration of 20 mg/L.

Reported statistics and error estimates:

probit analysis

Table: Results of test item

Test item concentration (nominal) [mg/L]	Respiratory rate test item [mg/L*h]	Phys.-chem. O2consumption [mg/L*h]	Respiratory rate - phys.-chem. O2consumption [mg/L*h]	Inhibition [%]
10	23.3	0.0*	23.3	0.0
100	22.7	0.0*	22.7	0.0
1000	20.3	0.0	20.3	4.3

* The physico-chemical oxygen consumption has been determined at 1000 mg/L test item concentration. As no physico-chemical oxygen consumption was observed at that test item concentration this observation also holds true for the lower test item concentrations.

Validity criteria fulfilled:

yes

Conclusions:

The substance showed 4.3 % respiration inhibition of activated sludge at a test item concentration of 1000 mg/L. The 3h-EC50 is higher than 1000 mg/L. Based on the PBTC concentration in the test item (50.4%), the result can be converted yielding a 3h-EC50 of 504 mg/l for the further consideration of this study.

Executive summary:

A study was performed to assess the toxicity of 2-phosphonatobutane-1,2,4-tricarboxylate acid to microorganisms. The study was conducted in accordance with Council Regulation (EC) No 440/2008, Method C.11 "Activated sludge respiration inhibition" (2008). This test method is equal to OECD Guideline 209 (1984). The activated sludge was exposed to a 50.4% aqueous solution of 2-phosphonatobutane-1,2,4-tricarboxylate acid at different concentrations. The respiration rate of each mixture was determined after aeration periods of 3 hours. The 50.4% aqueous solution of 2-phosphonatobutane-1,2,4-tricarboxylate acid (marketed as Bayhibit AM) showed 4.3 % respiration inhibition of activated sludge at a test item concentration of 1000 mg/L. The 3h-EC50 and the 3h-EC10 are therefore higher than 1000 mg/L. The effect value related to nominal concentration, since no analytical monitoring was performed. Based on the PBTC concentration in the test item (50.4%), the result can be converted yielding a 3h-EC50 of 504 mg/l for the further consideration of this study.

Description of key information

As there is no data available for tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate, results of the parent acid, 2-phosphonobutane-1,2,4-tricarboxylic acid are taken into account for this endpoint.
A 50.4% aqueous solution of 2-phosphonobutane-1,2,4-tricarboxylic acid showed 4.3 % respiration inhibition of activated sludge at a test item concentration of 1000 mg/L. The EC50 is higher than 1000 mg/L. Based on the amount of substance in the test item, the result can be converted yielding an EC50 of 504 mg/l for the further consideration of this study.

Key value for chemical safety assessment

EC50 for microorganisms:

504 mg/L

EC10 or NOEC for microorganisms:

504

Additional information

As there is no data available for tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate a read-across approach with the corresponding parent acid 2-phosphonobutane-1,2,4-tricarboxylic acid is proposed.

In aqueous media, tetrasodium hydrogen 2-phosphonatobutane-tricarboxylate and 2-phosphono-butane-1,2,4-tricarboxylic acid dissociate into the corresponding anion (2-phosphonatobutane-tricarboxylate ion) and the sodium ion and hydrogen ion (proton), respectively. Fate, behavior and the ecotoxicological properties of 2-phosphonobutane-1,2,4-tricarboxylic acid and its tetrasodium salt are thought to be an effect of the phosphonato-carboxylate ion rather than of the sodium ion or the hydrogen ion (proton), which are normal constituents in environmental systems and have no relevant ecotoxic properties in low concentrations.

Therefore a read-across between tetrasodium hydrogen 2-phosphonatobutane-tricarboxylate and 2-phosphonobutane-1,2,4-tricarboxylic acid is justified.

 

To assess the toxicity of 2-phosphonobutane-1,2,4-tricarboxylic acid to microorganisms, a study was conducted in accordance with Council Regulation (EC) No 440/2008, Method C.11 "Activated sludge respiration inhibition" (2008) - equivalent to OECD Guideline 209 (1984). The activated sludge was exposed to a 50.4% water solution of 2-phosphonobutane-1,2,4-tricarboxylic acid at different concentrations. The respiration rate of each mixture was determined after aeration periods of 3 hours. 2-phosphonobutane-1,2,4-tricarboxylic acid solution showed 4.3 % respiration inhibition of activated sludge at a test item concentration of 1000 mg/L. The EC50 is higher than 1000 mg/L. The effect value related to nominal concentration of the water solution, since no analytical monitoring was performed. Therefore the effect concentration can be converted based upon the water content of the test item, resulting in an EC10 and EC50 of 504 mg/l for further consideration of this study.