Strontium oxide

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:

2016-01-21

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study including analytical monitoring

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2011-02-07

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
not applicable

Analytical monitoring:

yes

Details on sampling:

- Concentrations: Samples from test start were taken before inoculum was added. Samples from test end were centrifuged to remove suspended solids. All samples for the chemical analysis were filtered through 0.22 μm PES filter (polyethylensulfone, Nalgene, bottle top filter). Exactly 20 mL of aqueous samples were transferred into disposable 50 mL polyethylene vials (Sarstedt, Nuembrecht, Germany), and acidified by addition of 200 μL of conc. nitric acid for stabilization. After storage, three control samples, the abiotic control and the three samples of the highest concentration were analysed.
- Sampling method: Exactly 20 mL of aqueous samples were transferred into disposable 50 mL polyethylene vials (Sarstedt, Nuembrecht, Germany), and acidified by addition of 200 μL of conc. nitric acid for stabilisation.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The test item was added directly into the test vessels. The required mass to obtain accurate test concentrations was applied on pieces of Teflon, which were subsequently added to the dilution water. To achieve a maximum dilution of the test item, the assay was stirred for 20 ± 2 h.
- Controls: Control (blank), abiotic control and reference assay

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Source: Fresh samples of activated sludge; withdrawn on 20-01-2016 from sewage treatment plant "Ruhrverband Kläranlage, Sunthelle 6, 57392 Schmallenberg, Germany; mainly fed with municipal wastewater
- Preparation of inoculum for exposure: Supernatant from settled sludge was decanted before the slugde was washed one time. A stock solution of activated sludge in tap water was prepared with a mixed liquor suspended solids level of 3.5 g dry mass sludge/L.
- Pretreatment: Sludge stock solution was fed with 50 mL/L synthetic sewage feed and incubated areated overnight at 20 ± 2°C in the dark.
- Initial biomass concentration: Mixed liquor suspended solids level in the test vessel was nominally 1.5 g/L.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

20°C at test start and end

pH:

pH 7.15 - 8.51

Nominal and measured concentrations:

The nominal treatment concentrations during the incubation phase were slightly lower as indicated in the study plan due to a calculation error. Since respiration inhibition was not observed up to the highest treatment level, this deviation is assessed to be without influence on reliability of the study.

Nominal added strontium neodecanoate concentration: 8.9, 87.5, 871.3 mg Strontium neodecanoate/L (in terms of pure substance, corresponding to 1.7, 16.5, 163.8 mg Sr). Measured concentration at the start and end of 3 h exposure period are within 88 to 95% of the nominal test concentration.

Details on test conditions:

TEST SYSTEM
- Test vessel: 1L Erlenmeyer flask
- Material, size, headspace, fill volume: 500 mL
- Aeration: during incubation (air flow 0.5-1 L/min)
- No. of organisms per vessel: MLSS level was nominally 1.5 g/L
- No. of vessels per concentration (replicates): one for test concentrations 8.9 and 87.5 mg/L (corresponding to 1.7 and 16.5 mg/L Sr); 3 replicates for the highest concentration 871.3 mg/L (corresponding to 163.8 mg/L Sr)
- No. of vessels per control (replicates): 6

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: deionised water, free from inhibitory concentrations of toxic substances

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
The microbial respiration rate of activated sludge was measured after 3 hours.

TEST CONCENTRATIONS
- Test concentrations: nominal added strontium neodecanoate concentration: 8.9, 87.5 and 871.3 mg Strontium neodecanoate/L (corresponding to 1.7, 16.5 and 163.8 mg Sr/L).

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 163.8 mg/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: (analytically verified)

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 163.8 mg/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: (analytically verified)

Details on results:

An inhibition of the respiration rate (compared to the control) was not observed at the highest test concentration of 871.3 mg strontium neodecanoate/L, corresponding to 163.8 mg strontium/L.

Results with reference substance (positive control):

The EC50 of the reference substance amounts to 10 mg/L and is within the accepted range of 2-25 mg/L.

Validity criteria fulfilled:

yes

Conclusions:

The EC10 and EC50 for the 3-h respiration inhibition of activated sludge are estimated with > 163.8 mg strontium per litre (nominal, analytically verified), the highest concentration tested.

Description of key information

The assessment of aquatic toxicity of strontium oxide to aquatic microorganisms is based on elemental strontium concentrations. Read-across of aquatic toxicity data available for soluble strontium substances is applied since strontium ions determine the ecotoxicological potential of strontium oxide.