Zirconium propionate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

22 Nov - 22 Nov 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP-Guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

See test conditions.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- A mixed population of activated sludge micro-organisms was obtained on 21 November 2012 from the aeration stage of the Severn Trent Water Public sewage treatment plant at Loughborough, Leicestershire, UK, which treats predominantly domestic sewage.
- The activated sewage sludge sample was maintained on continuous aeration in the laboratory at a temperature of appoximately 21°C overnight prior to use in the test.
- The SS concentration was equal to 3.0 g/L prior to use.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Hardness:

not stated

Test temperature:

20 ± 2 °C

pH:

Tap water: 8.14
Activated sludge: Pre-test: 6.6, Main test: 7.0
Main test, measured at the end of the test:
- Controls: 7.5 - 7.6
- Positive controls: 7.7 - 8.5
- Test item: 7.6 - 8.5

Dissolved oxygen:

Dissolved oxygen was measured after 30 minutes contact time. In some instances, the initial and final dissolved oxygen concentrations were outside those recommended in the test guidelines (7.0 mg O2/L and 2.0 mg O2/L, respectively). This was considered to have had no adverse effect on the results of the study given that in all cases the oxygen consumption was determined over the linear portion of the oxygen consumption trace.

Nominal and measured concentrations:

10, 100 and 1000 mg/L (nominal, based on anhydrous zirconium acetate)

Details on test conditions:

TEST SYSTEM
- Test vessel: 500 mL (16 mL synthetic sewage, 250 mL tap water or tap water + stock solution, 250 mL inoculum)
- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates): 4
- Dry matter in the test: 3 g suspended solids/L


PRE-TEST
- An amount of test item (11590 mg) was dissolved in water and the volume adjusted to 1 liter to give a 2500 mg a.i./L stock solution from which dilutions were made to give 250 and 25 mg a.i./L stock solutions. The 2500 mg a.i./L stock solution was adjusted to pH 7-8. On pH adjustment the test item dropped out of solution and was observed as a cloudy dispersion, however, this was considered acceptable for use in the test. An aliquot (200 mL) of the 25 mg a.i./L stock solution was dispersed with synthetic sewage (16 mL), activated sewage sludge (250 mL) and tap water to a final volume of 500 mL, to give the required test concentration of 10 mg a.i./L. similarly, aliquots (200 mL) of the 250 mg a.i./L and 2500 mg a.i./L stock solutions were used to prepare the test concentrations of 100 and 1000 mg a.i./L. The 1000 mg/L test concentration was prepared in triplicate. The volumetric flasks containing the stock solutions were inverted several times to ensure homogeneity of the stock solutions.

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol (CAS No. 591-35-5

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Remarks:

zirconium acetate, anhydrous

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Remarks:

zirconium acetate, anhydrous

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 530 mg/L

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Zr

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 530 mg/L

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Zr

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

The test item contained 40% anhydrous zirconium acetate (i.e. the active ingredient).
The effect of the test item on the respiration of activated sewage sludge gave a 3-hr EC50 value of greater than 1000 mg a.i./L. The No Observed Effect Concentration (NOEC) after 3 hours exposure was >= 1000 mg a.i./L. It was considered unnecessary and unrealistic to test at concentrations in excess of 1000 mg a.i./L.
At the Sponsors request the test concentrations have also been calculated based on zirconium (%w/w): 10, 100 and 1000 mg a.i./L are equivalent to 8, 74 and 742 mg Zr/L.

The dissolved oxygen concentrations in all vessels were less than 60% of the dissolved oxygen saturation level of 8.9 mg O2/L with the exception of control R1, reference item 10 and 32 mg/L and test item 100 mg a.i./L. This deviation was considerd to have had no adverse effect on the study given that all oxygen consumption values were measured/calculated over the linear portion of the traces.

The coefficient of variation of oxygen update in the control vessel was 4.2% and the specific respiration rate of the controls was 26.89 mg O2 per gram dw of sludge per hour.

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels:
EC50 = 15 mg/L (95% CI 13-18 mg/L)

Validity criteria fulfilled:

yes

Conclusions:

No statistically significant toxic effects were observed at all test concentrations employed. It was therefore considered justifiable not to perform a definitive test. The relatively large increase in respiration rate observed in the test vessels at 1000 mg a.i./L was considered to be due to metabolism of the acetate component of the test item. The 3-h EC50 and NOEC were determined to be > 1000 mg/L and >= 1000 mg/L anhydrous zirconium acetate, respectively, equivalent to >530 mg/L and ≥530 mg/L zirconium.

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the substance is highly insoluble in water, hence indicating that aquatic toxicity is unlikely to occur

Description of key information

Based on analysis of thermodynamic stability of aqueous zirconium species, the concentration of free Zr4+ ions under environmental conditions is barely detectable. Ionic zirconium (Zr4+) at relevant pH conditions (pH 7 - 8) of aquatic and terrestrial environments will rapidly transform to zirconium-oxide and -hydroxide complexes, precipitate and not be bioavailable to aquatic organisms. In accordance with REACH Annex VIII, 9.1.4 column 2, a study on toxicity to aquatic microorganisms does not need to be conducted if the substance is highly insoluble in water. Microorganisms in the STP will not be exposed to ZrO2, as it will either be removed in the primary settling tank before reaching the microorganisms, or it will not be bioavailable due to complexation. Furthermore ZrO2 is highly insoluble in water and consequently no study needs to be performed.

A standard activated sludge respiration inhibition study was still performed with zirconium acetate. No statistically significant toxic effects were observed at all test concentrations employed. The 3-h EC50 and NOEC were determined to be >1000 mg/L and ≥1000 mg/L anhydrous zirconium acetate, respectively, equivalent to >530 mg/L and ≥530 mg/L zirconium.

Key value for chemical safety assessment

EC50 for microorganisms:

530 mg/L