Ditantalum pentaoxide

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 November 2000 - 24 November 2000

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study conducted to GLP in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results.

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

yes

Remarks:

No analytical determination of concentration performed due to low solubility of test substance.

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Deviations:

yes

Remarks:

No analytical determination of concentration performed due to low solubility of test substance.

Principles of method if other than guideline:

Deviations not considered to have affected the validity of the test.

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
1.1 mg of the test substance were added directly to 1 litre of dilution water and treated for 1 h in an ultrasonic bath and afterwards stirred for 24 h on a magnetic stirrer. Finally undissolved particles of the test substance were removed by filtration.

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

Test Species: Scenedesmus subspicatus CHODAT
Source: Non-axenic strain of the test species obtained from 'The Collection of Algal Cultures' of the Institute of Plant Physiology at the University of Gottingen (Germany)
Maintenance of stock cultures: Exponentially-growing stock cultures are maintained in the test facility under constant temperature conditions (23 +/- 2°C) at a light intensity in the range 60 - 120 µE. x m^-2 x s^-1 (measured in the range 400 to 700 nm using a spherical quantum flux meter). The nutrient medium (according to BRINGMANN & KUHN (1977) is renewed once a week. Cell density measurements are made using a microcell counter.
Preparation of pre-cultures: Pre-cultures are set up three days before the start of a test. They are grown under identical exposure conditions as the stock cultures, except from the use of a different nutrient medium.
Test cultures: The algal inocula for a test are taken from an exponentially-growing pre-culture and are mixed with the nutrient medium to make up to a final cell density of about 10^4 cells per ml in the test medium.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Post exposure observation period:

None

Hardness:

NDA

Test temperature:

21 - 25 °C

pH:

pH 8.0 - 10.3

Dissolved oxygen:

NDA

Salinity:

N/A

Nominal and measured concentrations:

Test concentration/s (nominal): 1 mg/L

Details on test conditions:

EXPERIMENTAL PROCEDURE
In the main test, the algae are exposed to the test substance added to water at a range of concentrations for a period of 72 hours. Defined concentrations of the test substance will lead to a certain inhibition of algal growth and growth rate at the end of the 72 hour study period. Cell densities are recorded at 24-hour intervals. The 72 hour EC 50 (based on both, growth [b] and growth rate [r], is calculated or read from the concentration/percentage response curve. During the test a temperature range of 21 - 25°C is to be maintained in the test vessels. The pH is measured at the beginning of the test and at 72 hours.

The cell density in the control cultures should increase by a factor of at least 16 within 72 hours.

In order to avoid an impairment of the test system, an additional replicate is used for analysis and pH measurement at the beginning of the test (control: replicate VII; test concentrations: replicate IV). Analysis and pH measurement at the end of the test are performed using replicate I.

In order to check whether or not significant amounts of the test substance are incorporated into the algal biomass during the test period, a test flask at the highest test concentration without algae is run in parallel to the geometric series of test concentrations.

EXPOSURE CONDITIONS
Test vessels: 300 mL Erlenmeyer flasks with stoppers
Culturing apparatus: Light chamber in which a temperature in the range 21°C to 25°C can be maintained at +/- 2°C, and continuous uniform illumination is provided in the spectral range 400 to 700 nm.
Light intensity: At the average of the test solutions, a light intensity in the range 60 to 120 µE. x m^-2 x s^-1, or an equivalent range of 6.000 to 10.000 lx, is recommended to use.
Cell density measurements: Cell densities are measured in a microcell counter or, alternatively, are determined by means of a microscopic counting chamber.
Experimental design:
> 1 test concentration plus 1 control
> 3 replicates per concentration, 6 replicates per control
> initial cell density in the test cultures approximately 10^4 cells per millilitre
Test concentration/s (nominal): 1 mg/L
Method of administration: direct weighing
Duration of exposure: 72 hours

Criteria of effects:
The criteria of adverse effects used in this study were the substance-induced inhibition of growth [b] and growth rate [r], respectively, of the algal population.

Nutrient medium of pre-cultures and test cultures:
Nutrient Concentration in stock solution Final concentration in the solution of the pre- and test cultures

Stock solution 1: macro-nutrients
NH4Cl 1.5 g/L 15 mg/L
MgCl2 x 6 H2O 1.2 g/L 12 mg/L
CaCl2 x 2 H2O 1.8 g/L 18 mg/L
MgSO4 x 7 H2O 1.5 g/L 15 mg/L
KH2P04 0.16 g/L 1.6 mg/L

Stock solution 2: Fe-EDTA
FeCl3 x 6 H2O 80 mg/L 80 µg/L
Na2EDTA x 2 H2O 100 mg/L 100 µg/L

Stock solution 3: trace elements
H3BO3 185 mg/L 185 µg/L
MnCl2 x 4 H2O 415 mg/L 415 µg/L
ZnCl2 3 mg/L 3 µg/L
CoCl2 x 6 H2O 1.5 mg/L 1.5 µg/L
CuCl2 x 2 H2O 0.01 mg/L 0.01 µg/L
Na2MoO4 x 2 H2O 7 mg/L 7µg/L

Solid NaHCO3 is added to the nutrient media to make up a final concentration of 50 mg/L in the solutions of the pre-cultures and test cultures.

Reference substance (positive control):

no

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Details on results:

Analysis of the growth and growth rate of the algal population within the 72 h exposure period give the following results:

No toxic effects against algae at 1 mg/L.

The test result is expressed in terms of nominal concentration.
Considering the low aqueous solubility of the test substance (< 1 mg/L) no specific analysis was established.

Results with reference substance (positive control):

N/A

Reported statistics and error estimates:

None

Table 1: Growth rates in control vessels

Replicate	Cell density [cells/mL] (initial cell density = 10^4cells/mL)			Growth (b) [integral of biomass]	Growth rate (r)
	24 h	48 h	72 h
I	63333	210000	456667	476667	1.27
II	60000	220000	453333	481667	1.27
III	63333	213333	413333	458333	1.24
IV	63333	203333	433333	458333	1.26
V	66667	216667	413333	465000	1.24
VI	60000	210000	430000	460000	1.25
Ø	62778	212222	433333	466667	1.26

Growth (b)

Area under growth curve (Ø): 466667

Percentage inhibition of cell growth: 0.0

 

Growth rate (r)

Specific growth rate (Ø): 1.26

Percentage inhibition of cell growth rate: 0.0

 

Table 2: Growth rates in test vessels (1 mg/L)

Replicate	Cell density [cells/mL] (initial cell density = 10^4cells/mL)			Growth (b) [integral of biomass]	Growth rate (r)
	24 h	48 h	72 h
I	63333	213333	476667	490000	1.29
II	70000	220000	473333	501667	1.29
III	66667	216667	493333	505000	1.30
Ø	66667	216667	481111	498889	1.29

Growth (b)

Area under growth curve (Ø): 498889

Percentage increase of cell growth: -6.9

 

Growth rate (r)

Specific growth rate (Ø): 1.29

Percentage increase of cell growth rate: -2.8

 

SUMMARY OF RESULTS

Table 3: Mean cell density during the test:

Nominal concentration [mg/L]	Cell density [cells/mL] (initial cell density = 10^4cells/mL)
	24h	48h	72h
Control 1	62778 66667	212222 216667	433333 481111

               

Table 4: Mean growth (b) [integral of biomass]:

Nominal concentration [mg/L]	Area under growth curve	Inhibition (+) / Increase (-) [%]
Control 1	466667 498889	0.0 -6.9

                               

Table 5: Mean growth rate (r):

Nominal concentration [mg/L]	Growth rate [1/d]	Inhibition (+) / Increase (-) [1%]
Control 1	1.26 1.29	0.0 -2.8

Validity criteria fulfilled:

yes

Conclusions:

No toxic effects against algae at 1 mg/L.

Executive summary:

The acute aquatic toxicity of the test substance to algae was examined in a 72 hour static study using Scenedesmus subspicatus. The study was conducted in accordance with EEC Methods for Determination of Ecotoxicity Annex to Directive 92/69/EEC (O.J. No. L383A, 29.12.92) Part C, Method 3 'Algal inhibition test' which is in most parts equivalent to the OECD Guideline for Testing of Chemicals No. 201 'Alga, Growth Inhibition Test'.

No toxic effects against algae were observed at the only concentration of 1 mg/L.

Description of key information

The aquatic toxicity of ditantalum pentaoxide to aquatic algae and cyanobacteria was studied in Desmodesmus subspicatus at a nominal loading of 1 mg/L according to guidelines OECD 201 and  EU Method C.3 (Caspers, 2000). No adverse effects could be observed.

Based on the truly dissolved Ta concentrations measured in the T/D test according to OECD 29 (Klawonn 2022), ditantalum pentaoxide is considered highly insoluble. Therefore, aquatic toxicity is considered unlikely and no additional study to further investigate potential effects of ditantalum pentaoxide on freshwater algae is deemed necessary. The endpoint is waived in accordance with REACH Annex VII, endpoint 9.1.2, column 2.

Additional information

The key study (Casper, 2000) was conducted in line with GLP and standardised guidelines with a sufficient level of detail to assess the quality of the study. Desmodesmus subspicatus was exposed under static freshwater conditions to the test material for 72 hours. The algae were exposed to the test material at a nominal concentration of 1 mg/L. Under the conditions of the test no signs of toxicity were observed. The study determined the EC₀ of the test material to be ≥1 mg/L where the EC₅₀ is above the limits of solubility.