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Toxicity to aquatic algae and cyanobacteria

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Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
see section 13.1 for read-across justification
Reason / purpose:
read-across source
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Details on sampling:
To assess the concentration of dissolved tellurium, all test solutions were sampled at the beginning of the exposure periods prior to addition of the algae. At the end of each exposure period, samples were taken from each replicate of each treatment, pooled for chemical analysis and solutions and algae were separated using a 0.45 μm PET filter.
Vehicle:
no
Details on test solutions:
Due to the very low water solubility of the test item, a Water Accommodated Fraction (WAF) of was prepared according to the OECD guidance No. 23 to obtain an eluate used as the highest test concentration for the test.

A test preparation with a loading of 200 mg test item per 2 litre was prepared according to the OECD Guideline No. 23 and stirred using a star shape magnetic stirring bar for 72 h at room temperature (~20°C) for 72 hours. Finally, the test preparation was filtered by using a 0.2 μm filter (e.g. Sartolab 150v, PES-membrane, Sartorius Stedim Biotech S.A., Aubagne Cedex, France) according to OECD Guideline No. 29 to separate insoluble parts from the aqueous phase.

A volume of 100 mL of the filtrated WAFs was directly used as highest test concentration for the algal growth test. The filtrated WAF was then diluted with growth medium under sterile conditions to obtain the other four test concentrations. To obtain the nominal concentrations of 31.6, 10.0, 3.16 and 1.0 mg test item/L 158, 50, 15.8 and 5 mL of the filtrated WAF were diluted to 500 mL in a volumetric glass flask.

Test media:
The sterilised synthetic OECD medium according to OECD 201 was used as growth medium. As stated in the guideline OECD 201, the molar ratio of EDTA to iron slightly exceeds unity in this medium. This prevents iron precipitation and at the same time, chelation of heavy metal ions is minimised (molar ratio EDTA / Fe(III+) = 1.135). Considering the molar ratio and the stability constants of EDTA with Fe(III+) (log Ks are 25.0), it is assumed that the chelation of tellurium dioxide remains negligible in comparison with nominal test concentrations. In a pre-test it was demonstrated that the growth of P. subcapitata in the OECD 201 growth medium with 50 % EDTA concentration fulfils the validity criteria of the OECD 201 guideline while it did not in an EDTA-free OECD 201 medium. All stock solutions and the medium were prepared with purified water processed using an ELGA „PURELAB Ultra“.

Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Common name: Pseudokirchneriella subcapitata,
- Strain: Pseudokirchneriella subcapitata, Chlorophycea, Chlorophyta.
- Source (laboratory, culture collection): SAG, Culture Collection of Algae at Pflanzenphysiologisches Institut of the University at Göttingen, Albrecht von Haller Institut, Untere Klarspüle 2, D-37073 Göttingen, Catalog No 61.81 SAG.
- Age of inoculum (at test initiation): no data
- Method of cultivation: The stock cultures are maintained fulfilling the criteria of the OECD guideline 201.

ACCLIMATION

- Culturing media and conditions (same as test or not):
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
22.5 to 23.0
pH:
pH of control solutions at test start and end of the exposure period: 8.08 and 9.32 – 9.55
Nominal and measured concentrations:
nominal: 100, 31.6, 10.0, 3.16 and 1.0 mg test item/L (tellurium dioxide)
measured: 14.7, 4.174, 1.418, 0.422, 0.174 mg tellurium dioxide/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 250 mL conical glass flasks
- Aeration: The cultures were oscillated by continuously stirring on a laboratory shaker with 100 rpm
- Initial cells density: 1X10E4/ mL
- Control end cells density: 334.39 x 10E4/ mL
- No. of organisms per vessel: 676 μL at a cell density of 1.479 x 106 cells/mL
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 8


GROWTH MEDIUM
- Standard medium used: yes - EDTA and iron concentration adapted
- Detailed composition if non-standard medium was used:
The sterilised synthetic OECD medium according to OECD 201 was used as growth medium. As stated in the guideline OECD 201, the molar ratio of EDTA to iron slightly exceeds unity in this medium. This prevents iron precipitation and at the same time, chelation of heavy metal ions is minimised (molar ratio EDTA / Fe(III+) = 1.135). Considering the molar ratio and the stability constants of EDTA with Fe(III+) (log Ks are 25.0), it is assumed that the chelation of tellurium dioxide remains negligible in comparison with nominal test concentrations. In a pre-test it was demonstrated that the growth of P. subcapitata in the OECD 201 growth medium with 50 % EDTA concentration fulfils the validity criteria of the OECD 201 guideline while it did not in an EDTA-free OECD 201 medium. All stock solutions and the medium were prepared with purified water processed using an ELGA „PURELAB Ultra“.


TEST MEDIUM / WATER PARAMETERS
All stock solutions and the medium were prepared with purified water processed using an ELGA „PURELAB Ultra“.


OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: no
- Photoperiod: 24 hours
- Light intensity and quality: light intensity (OSRAM “day light”) adjusted to approximately 4440 - 8880 lux



EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: electronic particle counter (CASY 1 Model TT, Roche Diagnostics GmbH, Germany)


TEST CONCENTRATIONS
A non-GLP pre-test was performed with nominal loadings of tellurium dioxide of 0.1, 1.0, and 10.0 mg/L, without chemical analysis. Inhibition of algal growth rate of 26 % (yield 69 %) was observed at the 72 h mark by the tellurium dioxide concentration of 10.0 mg/L.
The NOEC was calculated at 1.0 mg/L.

Based on the results of the range-finder test, following nominal test concentrations of the definitive test were agreed upon with the monitor:
100, 31.6, 10.0, 3.16 and 1.0 mg/L.
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol, routinely checked
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
4.17 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
dissolved
Remarks:
Tellurium dioxide
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 14.7 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
dissolved
Remarks:
Tellurium dioxide
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
3.34 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
dissolved
Remarks:
Tellurium
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 11.7 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
dissolved
Remarks:
Tellurium
Basis for effect:
growth rate
Details on results:
In the growth inhibition test with Pseudokirchneriella subcapitata exposed to the test item over a period of 72 hours, the inhibition of growth rate was 18.5 % at the highest test concentration.
Therefore, no effect concentrations could be calculated and the EC50 for growth rate is estimated to > 14.7 mg test item/L.
The NOEC value for growth rate was calculated to be 4.17 mg test item/L.
For yield EC50 and EC10 values of 10.3 and 3.40 mg test item/L were calculated. The NOEC for yield was 1.42 mg test item/L.
Results with reference substance (positive control):
The nominal ErC50 value of 2.91 mg/L (95% confidence limits 2.35 - 3.63 mg/L) of the last test was in good agreement with the results of an international ring test with ErC50 of 3.38 ± 1.30 mg/L.
Reported statistics and error estimates:
The test results for yield were statistically analysed to determine an EC50, EC20 and EC10, and the respective 95 % confidence intervals, using Probit-analysis assuming log-normal distribution of the values. Individual replicate responses were used for the regression analysis. For growth rate EC
values could not be calculated since the inhibition was clearly below 50 % at the highest treatment.
The NOEC and LOEC values for growth rate and yield were determined by the Welch t-test for inhomogeneous variances or Williams Multiple
Sequential t-test using the computer program ToxRat Solutions.

Validity of the test:

The algae growth inhibition test with 2 consecutive exposure periods of 72 h each fulfils all validity criteria of the OECD guideline 201: The cell number in the control cultures increased by a factor of 334 within the test period of 72 h (validity criterion: > 16).

Evaluation of the sectional growth rates of the controls: The mean of the replicate coefficients of variations in the section-by-section growth rate of controls was 18.8 % during the test period of 3 days (validity criterion CV % 35 %).

The coefficient of variation of average specific growth rate at test end in replicate control cultures for the test periods was 0.9 % (validity criterion 7%).

Chemical analysis:

Tellurium concentrations of filtered samples (0.2 μm, Polyethersulfone membrane) were determined by ICP-MS (LOQ 0.063 μg Te/L)

At test end, the measured tellurium concentrations were between 90.9 and 112 % of the initial measured levels. Due to the stability of the test item during the test the growth test was evaluated using the measured initial concentrations.

Percent inhibition of growth rate and yield by the test item compared to controls after 72 h.

Measured test item [mg TeO2/L]

Nominal test item [mg TeO2/L]

% Inhibition of growth rate

% Inhibition of yield

Control

Control

0.0

0.0

0.174

1.0

-1.3

-8.0

0.422

3.16

-2.2

-13.3

1.418

10.0

-1.9

-11.7

4.174

31.6

2.8

14.8

14.65

100

18.5

66.1

 

Effect concentrations based on measured test item concentrations for the exposure of P. subcapitata for 72 h.

Parameter

 

EC50 [mg TeO2/L]

EC10[mg TeO2/L]

NOEC [mg TeO2/L]

Growth rate (r)

Value

> 14.7

-

4.17

Yield (y)

Value

10.3

3.40

1.42

 

95 %-cl lower

9.63

2.94

 

 

95 %-cl upper

10.90

3.83

 

Validity criteria fulfilled:
yes
Conclusions:
Growth rate:
EC50: > 14.7 mg tellurium dioxide/L (> 11.7 mg tellurium /L)
NOEC: 4.17 mg tellurium dioxide/L (3.34 mg tellurium/L)
 
Yield:
EC50: 10.3 mg tellurium dioxide/L (8.19 mg tellurium/L)
EC10: 3.40 mg tellurium dioxide/L (2.72 mg tellurium/L)
NOEC: 1.42 mg tellurium dioxide/L (1.13 mg tellurium/L)
 
Executive summary:

A study was performed to determine the toxicity of the test item “Tellurium dioxide” on the growth of the uni-cellular fresh water green alga Pseudokirchneriella subcapitata. Exponentially-growing cultures of the alga were exposed to various dilutions of a water accommodated fraction of the test item (WAF) obtained with a loading rate of 100 mg/L. The algae were exposed over several generations under defined conditions for a period of 72 hours according to the OECD guideline 201. For the determination of algal growth eight replicates of the control (test medium only) and four replicates of each test concentration were exposed to nominal concentrations of 1.0, 3.16, 10.0, 31.6 and 100 mg test item/L.

The concentrations of the dissolved tellurium were determined using ICP-MS at start and end of the test. The tellurium concentrations were stable during the test period (91 and 112 % of the initial measured levels) and the initial measured test item concentrations were used for the evaluation, based on the measured tellurium levels (0.174, 0.422, 1.42, 4.17 and 14.7 mg tellurium dioxide/L). The test item concentration was calculated from the measured tellurium concentrations using a factor of 1.251 (Te molecular weight 127.61 g/mol; TeO2 molecular weight 159.61 g/mol).

For the relevant measurement parameter growth rate, a slight inhibition of 18.5 % was observed at the highest test concentration. There was a concentration-dependent effect on the cell number increase (yield) of P. subcapitata starting at the second highest concentration of 4.17 mg TeO2/L.

 

Growth rate:

EC50: > 14.7 mg tellurium dioxide/L (> 11.7 mg tellurium /L)

NOEC: 4.17 mg tellurium dioxide/L (3.34 mg tellurium/L)

 

Yield:

EC50: 10.3 mg tellurium dioxide/L (8.19 mg tellurium/L)

EC10: 3.40 mg tellurium dioxide/L (2.72 mg tellurium/L)

NOEC: 1.42 mg tellurium dioxide/L (1.13 mg tellurium/L)

 

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
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Details on sampling:
To assess the concentration of dissolved tellurium, all test solutions were sampled at the beginning of the exposure periods prior to addition of the algae. At the end of each exposure period, samples were taken from each replicate of each treatment, pooled for chemical analysis and solutions and algae were separated using a 0.45 μm PET filter.
Vehicle:
no
Details on test solutions:
Due to the very low water solubility of the test item, a Water Accommodated Fraction (WAF) of was prepared according to the OECD guidance No. 23 to obtain an eluate used as the highest test concentration for the test.

A test preparation with a loading of 200 mg test item per 2 litre was prepared according to the OECD Guideline No. 23 and stirred using a star shape magnetic stirring bar for 72 h at room temperature (~20°C) for 72 hours. Finally, the test preparation was filtered by using a 0.2 μm filter (e.g. Sartolab 150v, PES-membrane, Sartorius Stedim Biotech S.A., Aubagne Cedex, France) according to OECD Guideline No. 29 to separate insoluble parts from the aqueous phase.

A volume of 100 mL of the filtrated WAFs was directly used as highest test concentration for the algal growth test. The filtrated WAF was then diluted with growth medium under sterile conditions to obtain the other four test concentrations. To obtain the nominal concentrations of 31.6, 10.0, 3.16 and 1.0 mg test item/L 158, 50, 15.8 and 5 mL of the filtrated WAF were diluted to 500 mL in a volumetric glass flask.

Test media:
The sterilised synthetic OECD medium according to OECD 201 was used as growth medium. As stated in the guideline OECD 201, the molar ratio of EDTA to iron slightly exceeds unity in this medium. This prevents iron precipitation and at the same time, chelation of heavy metal ions is minimised (molar ratio EDTA / Fe(III+) = 1.135). Considering the molar ratio and the stability constants of EDTA with Fe(III+) (log Ks are 25.0), it is assumed that the chelation of tellurium dioxide remains negligible in comparison with nominal test concentrations. In a pre-test it was demonstrated that the growth of P. subcapitata in the OECD 201 growth medium with 50 % EDTA concentration fulfils the validity criteria of the OECD 201 guideline while it did not in an EDTA-free OECD 201 medium. All stock solutions and the medium were prepared with purified water processed using an ELGA „PURELAB Ultra“.

Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Common name: Pseudokirchneriella subcapitata,
- Strain: Pseudokirchneriella subcapitata, Chlorophycea, Chlorophyta.
- Source (laboratory, culture collection): SAG, Culture Collection of Algae at Pflanzenphysiologisches Institut of the University at Göttingen, Albrecht von Haller Institut, Untere Klarspüle 2, D-37073 Göttingen, Catalog No 61.81 SAG.
- Age of inoculum (at test initiation): no data
- Method of cultivation: The stock cultures are maintained fulfilling the criteria of the OECD guideline 201.

ACCLIMATION

- Culturing media and conditions (same as test or not):
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
22.5 to 23.0
pH:
pH of control solutions at test start and end of the exposure period: 8.08 and 9.32 – 9.55
Nominal and measured concentrations:
nominal: 100, 31.6, 10.0, 3.16 and 1.0 mg test item/L (tellurium dioxide)
measured: 14.7, 4.174, 1.418, 0.422, 0.174 mg tellurium dioxide/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 250 mL conical glass flasks
- Aeration: The cultures were oscillated by continuously stirring on a laboratory shaker with 100 rpm
- Initial cells density: 1X10E4/ mL
- Control end cells density: 334.39 x 10E4/ mL
- No. of organisms per vessel: 676 μL at a cell density of 1.479 x 106 cells/mL
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 8


GROWTH MEDIUM
- Standard medium used: yes - EDTA and iron concentration adapted
- Detailed composition if non-standard medium was used:
The sterilised synthetic OECD medium according to OECD 201 was used as growth medium. As stated in the guideline OECD 201, the molar ratio of EDTA to iron slightly exceeds unity in this medium. This prevents iron precipitation and at the same time, chelation of heavy metal ions is minimised (molar ratio EDTA / Fe(III+) = 1.135). Considering the molar ratio and the stability constants of EDTA with Fe(III+) (log Ks are 25.0), it is assumed that the chelation of tellurium dioxide remains negligible in comparison with nominal test concentrations. In a pre-test it was demonstrated that the growth of P. subcapitata in the OECD 201 growth medium with 50 % EDTA concentration fulfils the validity criteria of the OECD 201 guideline while it did not in an EDTA-free OECD 201 medium. All stock solutions and the medium were prepared with purified water processed using an ELGA „PURELAB Ultra“.


TEST MEDIUM / WATER PARAMETERS
All stock solutions and the medium were prepared with purified water processed using an ELGA „PURELAB Ultra“.


OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: no
- Photoperiod: 24 hours
- Light intensity and quality: light intensity (OSRAM “day light”) adjusted to approximately 4440 - 8880 lux



EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: electronic particle counter (CASY 1 Model TT, Roche Diagnostics GmbH, Germany)


TEST CONCENTRATIONS
A non-GLP pre-test was performed with nominal loadings of tellurium dioxide of 0.1, 1.0, and 10.0 mg/L, without chemical analysis. Inhibition of algal growth rate of 26 % (yield 69 %) was observed at the 72 h mark by the tellurium dioxide concentration of 10.0 mg/L.
The NOEC was calculated at 1.0 mg/L.

Based on the results of the range-finder test, following nominal test concentrations of the definitive test were agreed upon with the monitor:
100, 31.6, 10.0, 3.16 and 1.0 mg/L.
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol, routinely checked
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
4.17 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
dissolved
Remarks:
Tellurium dioxide
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 14.7 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
dissolved
Remarks:
Tellurium dioxide
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
3.34 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
dissolved
Remarks:
Tellurium
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 11.7 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
dissolved
Remarks:
Tellurium
Basis for effect:
growth rate
Details on results:
In the growth inhibition test with Pseudokirchneriella subcapitata exposed to the test item over a period of 72 hours, the inhibition of growth rate was 18.5 % at the highest test concentration.
Therefore, no effect concentrations could be calculated and the EC50 for growth rate is estimated to > 14.7 mg test item/L.
The NOEC value for growth rate was calculated to be 4.17 mg test item/L.
For yield EC50 and EC10 values of 10.3 and 3.40 mg test item/L were calculated. The NOEC for yield was 1.42 mg test item/L.
Results with reference substance (positive control):
The nominal ErC50 value of 2.91 mg/L (95% confidence limits 2.35 - 3.63 mg/L) of the last test was in good agreement with the results of an international ring test with ErC50 of 3.38 ± 1.30 mg/L.
Reported statistics and error estimates:
The test results for yield were statistically analysed to determine an EC50, EC20 and EC10, and the respective 95 % confidence intervals, using Probit-analysis assuming log-normal distribution of the values. Individual replicate responses were used for the regression analysis. For growth rate EC
values could not be calculated since the inhibition was clearly below 50 % at the highest treatment.
The NOEC and LOEC values for growth rate and yield were determined by the Welch t-test for inhomogeneous variances or Williams Multiple
Sequential t-test using the computer program ToxRat Solutions.

Validity of the test:

The algae growth inhibition test with 2 consecutive exposure periods of 72 h each fulfils all validity criteria of the OECD guideline 201: The cell number in the control cultures increased by a factor of 334 within the test period of 72 h (validity criterion: > 16).

Evaluation of the sectional growth rates of the controls: The mean of the replicate coefficients of variations in the section-by-section growth rate of controls was 18.8 % during the test period of 3 days (validity criterion CV % 35 %).

The coefficient of variation of average specific growth rate at test end in replicate control cultures for the test periods was 0.9 % (validity criterion 7%).

Chemical analysis:

Tellurium concentrations of filtered samples (0.2 μm, Polyethersulfone membrane) were determined by ICP-MS (LOQ 0.063 μg Te/L)

At test end, the measured tellurium concentrations were between 90.9 and 112 % of the initial measured levels. Due to the stability of the test item during the test the growth test was evaluated using the measured initial concentrations.

Percent inhibition of growth rate and yield by the test item compared to controls after 72 h.

Measured test item [mg TeO2/L]

Nominal test item [mg TeO2/L]

% Inhibition of growth rate

% Inhibition of yield

Control

Control

0.0

0.0

0.174

1.0

-1.3

-8.0

0.422

3.16

-2.2

-13.3

1.418

10.0

-1.9

-11.7

4.174

31.6

2.8

14.8

14.65

100

18.5

66.1

 

Effect concentrations based on measured test item concentrations for the exposure of P. subcapitata for 72 h.

Parameter

 

EC50 [mg TeO2/L]

EC10[mg TeO2/L]

NOEC [mg TeO2/L]

Growth rate (r)

Value

> 14.7

-

4.17

Yield (y)

Value

10.3

3.40

1.42

 

95 %-cl lower

9.63

2.94

 

 

95 %-cl upper

10.90

3.83

 

Validity criteria fulfilled:
yes
Conclusions:
Growth rate:
EC50: > 14.7 mg tellurium dioxide/L (> 11.7 mg tellurium /L)
NOEC: 4.17 mg tellurium dioxide/L (3.34 mg tellurium/L)
 
Yield:
EC50: 10.3 mg tellurium dioxide/L (8.19 mg tellurium/L)
EC10: 3.40 mg tellurium dioxide/L (2.72 mg tellurium/L)
NOEC: 1.42 mg tellurium dioxide/L (1.13 mg tellurium/L)
 
Executive summary:

A study was performed to determine the toxicity of the test item “Tellurium dioxide” on the growth of the uni-cellular fresh water green alga Pseudokirchneriella subcapitata. Exponentially-growing cultures of the alga were exposed to various dilutions of a water accommodated fraction of the test item (WAF) obtained with a loading rate of 100 mg/L. The algae were exposed over several generations under defined conditions for a period of 72 hours according to the OECD guideline 201. For the determination of algal growth eight replicates of the control (test medium only) and four replicates of each test concentration were exposed to nominal concentrations of 1.0, 3.16, 10.0, 31.6 and 100 mg test item/L.

The concentrations of the dissolved tellurium were determined using ICP-MS at start and end of the test. The tellurium concentrations were stable during the test period (91 and 112 % of the initial measured levels) and the initial measured test item concentrations were used for the evaluation, based on the measured tellurium levels (0.174, 0.422, 1.42, 4.17 and 14.7 mg tellurium dioxide/L). The test item concentration was calculated from the measured tellurium concentrations using a factor of 1.251 (Te molecular weight 127.61 g/mol; TeO2 molecular weight 159.61 g/mol).

For the relevant measurement parameter growth rate, a slight inhibition of 18.5 % was observed at the highest test concentration. There was a concentration-dependent effect on the cell number increase (yield) of P. subcapitata starting at the second highest concentration of 4.17 mg TeO2/L.

 

Growth rate:

EC50: > 14.7 mg tellurium dioxide/L (> 11.7 mg tellurium /L)

NOEC: 4.17 mg tellurium dioxide/L (3.34 mg tellurium/L)

 

Yield:

EC50: 10.3 mg tellurium dioxide/L (8.19 mg tellurium/L)

EC10: 3.40 mg tellurium dioxide/L (2.72 mg tellurium/L)

NOEC: 1.42 mg tellurium dioxide/L (1.13 mg tellurium/L)

 

Description of key information

Study was conducted according to OECD guideline 201, data are reliable without restrictions. 

Key value for chemical safety assessment

EC50 for freshwater algae:
11.7 mg/L

Additional information

The toxicity of Tellurium dioxide on the growth of the uni-cellular fresh water green alga Pseudokirchneriella subcapitata was tested in a study according to OECD guideline 201.

Alga were exposed to various dilutions of a water accommodated fraction of the test item (WAF) obtained with a loading rate of 100 mg/L.

For the relevant measurement parameter growth rate, a slight inhibition of 18.5 % was observed at the highest test concentration. There was a concentration-dependent effect on the cell number increase (yield) of P. subcapitata starting at the second highest concentration of 4.17 mg TeO2/L.

Growth rate:

EC50: > 14.7 mg tellurium dioxide/L (> 11.7 mg tellurium /L)

NOEC: 4.17 mg tellurium dioxide/L (3.34 mg tellurium/L)  

Yield:

EC50: 10.3mg tellurium dioxide/L (8.19 mg tellurium/L)

EC10: 3.40 mg tellurium dioxide/L (2.72 mg tellurium/L)

NOEC: 1.42 mg tellurium dioxide/L (1.13 mg tellurium/L)  

Justification for read-across:

This read-across is based on the hypothesis that source and target substances do possess similar ecotoxicological properties.

Since the physico-chemical behaviour of elemental Tellurium and Tellurium dioxide is the same with regard to their metabolic fate (reduction to the Telluride cation) there seems to be good evidence that Tellurium from different moieties will behave very similar with regard to systemic toxicity.

Elemental Tellurium and Tellurium dioxide are relatively poorly water soluble and their systemic uptake by environmental organisms will be directly comparable.

Thus the bioavailability will be an important factor for assessment of ecotoxicity of both substances. The water solubility of both substances is relatively low, with 1.7 and 2.5 mg/L for Tellurium and Tellurium dioxide, respectively.

Data from transformation dissolution tests at different pH values and loadings are available for both substances, indicating Tellurium dioxide to be more soluble at pH 8.

 

Corresponding standard information requirement

Source substance

Tellurium dioxide

Target substance

Tellurium

Water solubility

Transformation dissolution test: OECD guideline 29

 

Target pH 8 at 21.5 °C.

Loadings TeO2: Te concentrations after 7 days:

1 mg/L: 698.9 µg/L

10 mg/L: 6.254 mg/L

100 mg/L: 30.72 mg/L

Transformation dissolution test: OECD guideline 29

 

Target pH 8 at 21.5 °C.

Loadings: Te concentrations after 7 days:

1 mg/L: 20.02 µg/L

10 mg/L: 183.3 µg/L

100 mg/L:1.762 mg/L.

Water solubility:

OECD guideline 105

 

2.5 mg/L at 23 °C

pH 6.4

Water solubility:

OECD guideline 105

 

1.7 mg/L at 20 °C

pH 5.5 – 6.3

 

Underlying the basic assumption that effects caused by the bioavailable metal fraction and the same toxicokinetic behaviour (outlined in detail in the chapter toxicokinetic), ecotoxicity data from the relatively higher soluble Tellurium dioxide were considered appropriate for the ecotoxicity assessment of Tellurium.

In conclusion read-across is considered an appropriate adaptation for ecotoxicological endpoints to meet the standard information requirements according to REACH Regulation.

A detailed justification for read-across describing the toxicokinetic profile, comparing physico-chemical and toxicological properties as well as classification and labelling is outlined in IUCLID chapter 13 in a separate paper.