Strontium oxide

Water solubility

Administrative data

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2017-08-22 to 2017-09-29

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Version / remarks:

1995

Deviations:

yes

Remarks:

Two vessels were set up under argon in a parallel design, each vessel was sampled several times instead of one vessel at each sampling time. Mean temp. was 20.8 ± 0.4 °C instead of 20.0 ± 1.0 °C; turbidity ≥ 0.7 NTU (Sr conc. may include reac. products)

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Version / remarks:

2008

Deviations:

yes

Remarks:

Two vessels were set up under argon in a parallel design, each vessel was sampled several times instead of one vessel at each sampling time. Mean temp. was 20.8 ± 0.4 °C instead of 20.0 ± 1.0 °C; turbidity ≥ 0.7 NTU (Sr conc. may include reac. products)

GLP compliance:

yes (incl. QA statement)

Remarks:

signed, 2016-12-16

Type of method:

flask method

Test material

Test material information

Constituent 1

Reference substance name:

Strontium oxide

EC Number:

215-219-9

EC Name:

Strontium oxide

Cas Number:

1314-11-0

Molecular formula:

OSr

IUPAC Name:

Strontium oxide

Test material form:

solid

Details on test material:

Appearance: white/off-white

Specific details on test material used for the study:

Storage: Keep in original tightly closed container in a cool well-ventilated place. Keep container upright and protect from damage

Results and discussion

Water solubility

Water solubility:

7.63 g/L

Conc. based on:

test mat. (dissolved fraction)

Loading of aqueous phase:

42.01 g/L

Incubation duration:

>= 6 - <= 8 d

Temp.:

20 °C

pH:

13.2

Remarks on result:

other: SD: 0.04g/L, turbidity: ≥ 0.7

Details on results:

Observations
Strontium oxide reacts heavily with water under heat generation and precipitation of a white crystalline solid. After filtration and filtration followed by centrifugation the solution was visually clear but the measured turbidity was never below 0.7 NTU in these samples. Various approaches have been made to reduce the turbidity.

Temperature
The temperature in the thermostatically controlled incubation cabinet was monitored by a thermo data logger (Testo 175-T2. Testo AG. Leutkirch. Germany). The mean temperature was 20.8 ± 0.4 °C. During the study the maximum temperature was 21.3 °C and the minimum was measured to be 19.0 °C. Therefore, some measuring points were slightly above 21.0 °C and not within 20.0 °C ± 1.0 °C. However, the mean temperature was within the range given in the study plan.

Solution pH
The pH of solutions containing the test item increased to a pH value in the range of 13.1 – 13.2. The pH of method blanks remained constant at 6.1 – 6.5.
The pH was measured on sampling days using a Multi 9430 devices from WTW (Weilheim, Germany). Measurements were taken after readings had stabilized and waiting for an additional minute. The pH electrodes (Sentix 940-3) were calibrated every week during the test and checked on each sampling day.

Oxygen concentration
During the test, the oxygen concentration in the acrylic glass box was monitored with a MICRO IV oxygen sensor. Oxygen concentrations (in %) remained at about 0 %.

ICP-OES measurement
Stable strontium concentrations according to the study guideline OECD 105 as well as the Regulation 440/2008/EC A.6 were measured during the test from day 6 to day 8, i.e. an increase of Sr concentrations was not observed.

Sample a from vessel 1 after 7 days (diluted 10000-fold, 0.5 M nitric acid) exhibits a Sr concentration which was measured to be above the highest calibration (1000 µg/L) of the measurement series. Moreover, the concentration in this sample was above the amount the detector can register. This is denoted in the instrument software. The other samples of d6 exhibits concentrations of 617 - 619 µg Sr/L (diluted 10000-fold, 0.5 M nitric acid). Due to this the Sr concentration of this sample is considered as not to be valid and not used for further evaluation. This contamination of the sample might be due to a filter rupture. As the loading of the test item is very high, there is still a lot of strontium in solution/dispersion after centrifugation without preliminary filtration. Due to this considerationsthese considerations a repetition of measurement of this sample is considered not to be feasible.

Method blanks show increased Sr levels. That hints at cross contaminations (155.42 – 268.70 µg Sr/L = 0.0002 – 0.0003 g Sr/L). However, these values are far below concentrations in actual test item loaded samples (6.12– 6.52 g Sr/L) and therefore, have no influence on the validity of this study.

Any other information on results incl. tables

Method validation summary

validation parameter	results	comment
selectivity	strontium-selective wavelength of 407.771 nm	no matrix effects observed
linearity	applied calibration functions were linear	correlation coefficients were 0.999414 (pre-test) 0.999262 (main test)
limit of detection (LOD)	pre-test: 0.008 µg Sr/L main test: 0.014 µg Sr/L
limit of quantification (LOQ)	pre-test: 0.025 µg Sr/L main test: 0.043 µg Sr/L
method blanks	main test: Sr concentrations hints at cross contaminations (155.42 – 268.70 µg Sr/L = 0.0002 – 0.0003 g Sr/L) but far below conc. in actual test item loaded samples (6.12 – 6.52 g Sr/L)	method blanks
accuracy and precision	mean Sr recovery in CRM TMDA-52.4: main test: 101.1 ± 0.5 % (n = 4)	139 µg Sr/L (dilution 2-fold with 0.5 M nitric acid)
accuracy and precision	mean Sr recovery in CRM TMDA-70.2: main test: 99.6 ± 0.7 % (n = 4)	225 µg Sr/L (dilution 2-fold with 0.5 M nitric acid)
accuracy and precision	mean Sr recovery in quality control standard from Carl Roth: main test: 101.1 ± 0.5 % (n = 4)	Diluted to 600 µg Sr/L with 0.5 M nitric acid
accuracy and precision	mean Sr recovery in quality control standard #23: preliminary test: 102.8 ± 0.1 % (n = 2)	Diluted to 50 µg Sr/L with 0.5 M nitric acid
accuracy and precision	mean Sr recovery in quality control standard #23: preliminary test: 99.4 ± 1.2 % (n = 2)	Diluted to 500 µg Sr/L with 0.5 M nitric acid
accuracy and precision	mean Sr recovery in recalibration standard main test: 105.9 ± 0.6 % (n = 4)	Diluted to 500 µg Sr/L with 0.5 M nitric acid
accuracy and precision	mean Sr recovery in recalibration standard preliminary test: 108.1 ± 0.9 % (n = 2)	Diluted to 250 µg Sr/L with 0.5 M nitric acid
trueness	main test: Sr recoveries in fortified samples: 94.4 – 100.3 % (n = 5)

Applicant's summary and conclusion

Conclusions:

Strontium oxide is expected to heavily react with water to form Sr(OH)2, yielding a white precipitate in test vessels. After introducing the test item into the agon-purged water, a heavy reaction with generation of heat was observed.
Under the conditions of this test (flask method under protective gas atmosphere, loading of 42 g/L test item), it was technically not possible to separate solid/dispersed or colloidal from aqueous fractions. Measured turbidity in samples did not fall below 0.7 NTU, although various separation methods (diverse filtration and centrifugation approaches) were tested. Therefore, a major fraction of the measured Sr concentrations may originate from dispersed / colloidal reaction products.
Stable strontium concentrations were measured at 20.0 ± 1.0 °C and pH 13.2 on day 6, 7 and 8 amount to 6.26 ± 0.04 g Sr/L corresponding to SrO of 7.63 ± 0.04 g/L. Since it was technically not possible to separate solid/dispersed or colloidal from aqueous fractions, measured Sr concentrations may include dispersed / colloidal reaction products. Thus, the estimated solubility of SrO is expected to represent a worst case.