Barium zirconium trioxide

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

Deviations:

yes

Remarks:

Slight temperature deviation - not significant for the results of the test.

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

CES Ref#: 2018-0530
Bx #: WON 2958

Analytical monitoring:

yes

Remarks:

Analysis was carried out at an external laboratory on solutions supplied by Cheshire Eco Solutions

Details on sampling:

Appropriate sub-samples of the contents of each test vessel were removed after 24, 48 and 72 hours of incubation . Samples were supplied to Thermograde who arranged ICP analysis of the filtered sub samples for soluble Ba and Zr

Vehicle:

yes

Remarks:

OECD Nutrient Medium (Batch number OECD / 18006).

Details on test solutions:

Test material preparation: Water Accommodated Fractions (WAF's) containing concentrations of BARIUM ZIRCONATE over a range of 56.2, 100.0, 177.8, 316.2, 562.3, and 1000.0 mg/l were prepared in OECD test media. After a stirring and settling period the WAF's were observed to contain settled sediment on the bottom of the flasks and were increasingly cloudy with concentration. The central portion of each was siphoned and used as the test concentration.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

Supplier:Culture Collection of Algae and Protozoa, Ambleside.
Stock cultures were maintained in OECD Nutrient Medium in accordance with Cheshire Eco Solutions SOP 1.2.
Batch Number PSI 8001 (A) inoculation date 29.10.18.

Test type:

static

Water media type:

other: OECD Nutrient Medium (Batch number OECD / 18006).

Remarks:

The sample was found to be insoluble in freshwater and so Water Accommodated Fractions (WAF's) were prepared in the dilution media.

Total exposure duration:

72 h

Test temperature:

All parameters measured in this study lay within the acceptable tolerance limits with the exception of the initial temperatures which were slightly below the 21C lower tolerance limit. However the test flasks rapidly acclimated to the 21-24C target temperature range within one hour of being placed on the orbital shaker under illumination. This slight deviation did not affect the test outcome

pH:

6.04 (10.0 mg/l solution in Deionised water stirred for approx. 24 hours)

Nominal and measured concentrations:

The control sample, the 56.2 mg/l, the 100 mg/l and the 1000.0 mg/l were analysed. Barium zirconate is insoluble but there is a small amount of barium carbonate impurity which is sparingly soluble.
The values obtained for the Control sample (no added substance) and the test samples were as follows;
Control Ba = <0.1 mg/l; Control Zr = <0.1 mg/l
56.2 mg/l BaZrO3 - Ba = 1.2 mg/l, Zr = <0.1 mg/l
100 mg/l BaZrO3 - Ba = 2.1 mg/l, Zr = <0.1 mg/l
1000 mg/l BaZrO3 - Ba = 5.8 mg/l, Zr = <0.1 mg/l

Details on test conditions:

Test conditions: Six replicate control flasks and three replicate flasks at each test concentration, were prepared with algae added from a culture concentrate to give an initial algal cell concentration of approximately 9856 cells per ml. The culture flasks were incubated in a rotary incubator at a target temperature of 21-240C under continuous white light (4500-9000 lux) for 72 hours.

Reference substance (positive control):

yes

Remarks:

The reference material, 3,5-dichlorophenol was tested over a concentration range of 1.0, 1.78, 3.16, 5.62 and 10.0 mg/l prepared in OECD Nutrient Media from a 1.0 g/l stock solution (DCP-18005)

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

201.4 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

Microscopic examination indicated no unusual cell growth or deformity at any of the test concentrations. Negative inhibition was not observed after 72 hours in this study. The lowest concentration of test material producing complete (100%) inhibition of the test culture could not be determined after 72 hours in this study. There was clear evidence of a dose response in this study.

Results with reference substance (positive control):

The 3,5-Dichlorophenol Reference toxicant tested in this study produced a 72 hour EC50 value of 1.32 mg/l . This is slightly below the mean value for 3,5-DCP results (3.38 mg/l with 1.30 SD's) quoted in OECD 201 (via reference to the ISO 8692: 2012(E) method). However the method does state that a high number of outliers were observed due to the use of different growth media and the DCP reference test result is not one of the validity criteria for assessment within the OECD 201 method.

Summary Table

Time (Hours)	EC50 (mg/l)	95% Fiducial Limits (mg/l)		EC90 (mg/l)	95% Fiducial Limits (mg/l )	NOEC (mg/l)	LOEC (mg/l)
24	163.7	142.3	179.2
48	594.8	489.5	695.7
72	201.4	80.6	448.1	>1000.0	494.5 - 130511	<56.2	56.2

NOEC — No Observed Effect Concentration

LOEC — Lowest Observed Effect Concentration

EC10 value 72 hour: Calculated to be 35.0 mg/l

Conclusions:

In study CES180722 a sample of BARIUM ZIRCONATE was assessed for its potential toxicity to the freshwater alga Pseudokirchnereilla subcapitata in a static test over 72 hours according to the procedure described in OECD Guideline 201 Alga, Growth Inhibition Test and as detailed in Cheshire Eco Solutions SOP 111.20.
Water Accommodated Fractions (WAFs) containing concentrations of BARIUM ZIRCONATE, were prepared over the range 56.2 to 1000.0 mg/l .
Cultures of Pseudokirchnereilla subcapitata were exposed to determine the concentration which inhibited algal growth rate by 50% over 72 hours (EC50).
The 72 hr EC50 result was 201.4 mg/l

Description of key information

Water Accommodated Fractions (WAFs) containing concentrations of barium zirconate, were prepared over the range 56.2 to 1000.0 mg/l .

Cultures of Pseudokirchnereilla subcapitata were exposed to determine the concentration which inhibited algal growth rate by 50% over 72 hours (EC50).

The 72 hr EC50 result was 201.4 mg/l. The Ba2+ ion level in the 1000mg/l sample was determined to be ~5.2 mg/l at a pH of ~6.0.

Water solubility of this material is very low at around 5 mg/l as Ba2+ ions at a pH of ~ 8.0, and is likely to be due to barium carbonate impurity rather than the solubility of the barium zirconate ion itself.

The effect seen on the algal growth is likely to be associated with Ba ions in solution as a result of dissolution of barium carbonate impurity under the conditions of the test.

Key value for chemical safety assessment

EC50 for freshwater algae:

201.4 mg/L

EC10 or NOEC for freshwater algae:

35 mg/L