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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
Justification for type of information:
This information is used in a read-across approach in the assessment of the target substance.

Reason / purpose for cross-reference:
read-across source
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
54.1 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Remarks:
calculated sodium tungstate concentrations
Basis for effect:
growth rate
Remarks on result:
other: 95% CL 41.1 to 67.1
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
52.9 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
other: calculated sodium tungstate concentrations
Basis for effect:
growth rate
Remarks on result:
other: 95% CL 40.5-65.3 mg/L
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
< 10.9 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
other: calculated sodium tungstate concentrations
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC20
Effect conc.:
< 10.9 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
other: calculated sodium tungstate concentrations
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
< 10.9 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
other: calculated sodium tungstate concentrations
Basis for effect:
growth rate
Details on results:
- Exponential growth in the control (for algal test): yes
- Any stimulation of growth found in any treatment: none
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: none
- Effect concentrations exceeding solubility of substance in test medium: none
Results with reference substance (positive control):
N/A
Reported statistics and error estimates:
NOEC values were estimated using one-way ANOVA procedure and two-tailed Dunnett's test. Shiro-Wilke's and Levene's tests were also used as appropriate. EC values were calculated using a logistic model. All statistical analysis was conducted with SAS software.
Validity criteria fulfilled:
yes
Conclusions:
The 72 hour ErC50 of the test substance to P. subcapitata was found to be 52.9 mg sodium tungstate/L, with 95 % confidence limits of 40.5 - 65.3 mg sodium tungstate/L. The 72 hour NOErC was <10.9 mg sodium tungstate/L.
Executive summary:

In a 72 hour acute toxicity study, the cultures of Pseudokirchnerella subcapitata were exposed to sodium tungstate at mean measured concentrations of Control, 10.9, 21.9, 41.6, 84.5 and 168 mg sodium tungstate/L under static conditions in accordance with the OECD Guideline 201.  The NOEC/EC10 and EC50 values based on growth rate were < 10.9 mg/L and 52.9 mg/L, respectively.

No abnormalities were noted.

This toxicity study is classified as acceptable and satisfies the guideline requirements for an acute algae toxicity study.

 

Results Synopsis

 

Test Organism: P. subcapitata

Test Type: Static

 

72 hr NOEC/EC10: < 10.9 mg Na2WO4/L (corresponding to 6.82 mg W/L)

72 hr EC50: 52.9 mg Na2WO4/L (corresponding to 33.12 mg W/L)

 

Endpoint(s) Effected: growth rate and cell density

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
This information is used in a read-across approach in the assessment of the target substance.
Reason / purpose for cross-reference:
read-across source
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 20 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
sodium tungstate
Basis for effect:
growth rate
Remarks on result:
other: 95 % CL could not be calculated
Duration:
72 h
Dose descriptor:
EC20
Effect conc.:
15.6 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
sodium tungstate
Basis for effect:
growth rate
Remarks on result:
other: 95 % CL 14.7-16.6 mg/L
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
6.54 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
sodium tungstate
Basis for effect:
growth rate
Remarks on result:
other: 95 % CL 5.59-7.49 mg/L
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.85 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
concentration sodium tungstate
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
8.21 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
sodium tungstate
Basis for effect:
biomass
Remarks on result:
other: 95 % CL 7.27-9.15 mg/L
Duration:
72 h
Dose descriptor:
EC20
Effect conc.:
2.17 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
sodium tungstate
Basis for effect:
biomass
Remarks on result:
other: 95 % CL 1.61-2.73 mg/L
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.993 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
sodium tungstate
Basis for effect:
biomass
Remarks on result:
other: 95 % CL 0.622-1.36 mg/L
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.85 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
sodium tungstate
Basis for effect:
biomass
Details on results:
The number of algal cells in the control at test termination was greater than 16 times the number initially inoculated to verify logarithmic phase growth. The coefficient of variation for daily growth rates in the control replicates during the course of the test did not exceed 35 %. The coefficient of variation of average specific growth rates during the whole test period in control replicate did not exceed 7 %. Since the study was not conducted as a limit test, there were at least one test concentration exhibiting less than 50 % decrease in growth and once concentration exhibiting greater than 50 % decrease in growth relative to the control. The pH in the control did not increase more than 1.5 units during the study.
Reported statistics and error estimates:
All statistical analyses were performed with SAS software. NOEC values were calculated using ANOVA and Dunnett's tests. Shapiro-Wilk's and Levene's tests were conducted to test for normality and homogeneity of variance. EC estimates were calculated using a logistic model. Parametric analyses were performed on the 72-hour growth rate and yield data. Non-parametric analyses were performed on the 24- and 48-hour growth rate and yield data.

Percent inhibition of growth rate:

0.39 mg/L: 0 %

0.85 mg/L: 0 %

1.9 mg/L: 4 %

4.1 mg/L: 8 %

9.1 mg/L: 12 %

20 mg/L: 24 %

Validity criteria fulfilled:
yes
Conclusions:
The 72 hour EC50 for growth rate for P. subcapitata was >20 mg sodium tungstate/L, while the EC10 for growth rate was 6.54 mg sodium tungstate/L, with 95 % confidence limits of 5.59 and 7.49 mg/L. The 72 hour EC50 for yield was 8.21 mg/L, with 95 % confidence limits of 7.27 and 9.15 mg/L. The 72 hour NOEC was determined at 0.85 mg/L.
Executive summary:

In a 72 hour acute toxicity study, the cultures of Pseudokirchneriella supcapitata (Chlorophyceae) were exposed to sodium tungstate at nominal concentrations of 0.39, 0.85, 1.9, 4.1, 9.1, and 20 mg/L under static conditions in accordance with the OECD Guideline 201. The NOErC, ErC10 and ErC50 values based on growth rate were 0.85, 6.54, and > 20 mg/L, respectively.  The % growth inhibition in the treated algal culture as compared to the control ranged from 4 to 24 %.

 

This toxicity study is classified as acceptable and satisfies the guideline requirements for a 72 hour acute toxicity study with aquatic algae.

Results Synopsis

 

Test Organism: P. subcapitata

Test Type: Static

 

72 hr ErC10: 6.54 mg a.i./L                       95% C.I.:  5.59 to 7.49 mg a.i./L

72 hr ErC50:  > 20 mg a.i./L                95% C.I. could not be determined

72 hr NOErC: 0.85 mg a.i./L                  

Endpoint(s) Effected:  growth rate, yield (biomass)

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
This information is used in a read-across approach in the assessment of the target substance.

Reason / purpose for cross-reference:
read-across source
Duration:
72 h
Dose descriptor:
EC0
Effect conc.:
>= 1 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: biomass and growth rate
Details on results:
Growth
Area under growth curve: 408333
Percentage increase of cell growth: -7.9%

Growth rate
Specific growth rate: 1.19
Percentage increase of cell growth rate: -3.7%

Results with reference substance (positive control):
n/a
Reported statistics and error estimates:
NOEC and LOEC were determined according to DUNNETT (1955, 1964)

All results are expressed in terms of nominal concentrations. Considering the low aqueous solubility of the test substance (< 1 mg/L WO3 under exposure conditions) no specific analysis was established.

See attached results for final cell densities.

Validity criteria fulfilled:
not specified
Conclusions:
No toxic effects against algae at 1 mg/L. EC0 ≥ 1 mg/L
Executive summary:

In a 72 hour acute toxicity study, the cultures of Desmodesmus subspicatus were exposed to tungsten trioxide at a nominal concentration of 1 mg/L under static conditions in accordance with OECD Guideline 201 (EU C.3).  The NOEC (EC0) value based on growth rate and biomass was 1 mg WO3/L (corresponding to 0.79 mg W/L). 

No abnormalities were noted.

This toxicity study is classified as supplementary and satisfies the guideline requirements for an acute algae toxicity study.

 

Results Synopsis

 

Test Organism: D. subspicatus

Test Type: Static

 

72-hr NOEC: 1 mg WO3/L (corresponding to 0.79 mg W/L)

Endpoint(s) Effected: growth rate and cell density

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Description of key information

Read-across from tungsten trioxide and sodium tungstate was used for the assessment of the toxicity of tungsten hexachloride to aquatic algae:

In a 72-hr algal growth inhibition test with tungsten trioxide (Bayer, 2002) no toxic effects were observed at the saturation concentration under exposure conditions (1 mg tungsten trioxide/L).

Two growth inhibition tests using sodium tungstate (ABC Laboratories, 2009 & 2010) are available. The test conducted in 2009 applied a concentration between 0.39 and 20 mg/L. The ErC10 was 6.54 mg sodium tungstate/L. A ErC50 value is not available from this test.

The second test conducted in 2010 in the concentration range 10.9 - 168 mg/L resulted in an ErC50 of 52.9 mg sodium tungstate/L

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Recalculation of these values to corresponding concentrations of tungsten hexachloride result in theoretic values of:

- ErC10 = 8.26 mg WCl6/L

- ErC50 = 71.41 mg WCl6/L

However, these values considerably exceed the water solubility of the substance which is in the range of 20 - 42.1 µg/L and 44.8 µg/L after adjustment to pH 7 (Golz, 2017). Therefore, no adverse effects in freshwater algea are expected through the amount of soluble tungsten ions released from tungsten hexachloride in water.

Key value for chemical safety assessment

Additional information

Two toxicity tests were performed with sodium tungstate using two different concentration ranges in order to bracket the desired test endpoints (EC values and NOEC values) for the various growth parameters (yield and growth rate):

In the first study (ABC Laboratories, 2009), conducted at a nominal concentration range of 0.39 to 20 mg/L, inhibition of growth rate ranged from 0 % at the second lowest concentration to 24 % at the highest concentration. The ErC50 for growth rate was thus greater than 20 mg/L. The highest test concentration in which growth rate was not statistically significant different from the control, i.e. the NOEC, was 0.85 mg/L. This NOEC, however, must be considered as an artifact of the unusually low coefficient of variation that occurred in this test (0, 1 or 2% CV at all test concentrations). The next highest test concentration to the NOEC, 1.9 mg/L, exhibited only a 4 % inhibition of growth rate, and only 8 % inhibition occurred at 6.54 mg/L (corresponding to 3.83 mg W/L). These small effects are almost certainly not biologically significant, despite being statistically significant due to the unusual precision of the test. As stated in the ECHA guidance R10 (ECHA, 2008), when the statistical “power is high, it may occur that biologically unimportant differences are statistically significant“. There has been a recommendation within OECD to phase out the use of the NOEC, which also has the disadvantage of being highly dependent upon the selection of test concentrations and does not allow for the estimate of a confidence interval. An alternative, and according to ECHA, preferred method of expressing chronic toxicity is the use of the ErC10. The advantage of the use of a regression-based endpoint such as the ErC10 is that information from the entire concentration-effect relationship is used and confidence intervals can be calculated.

The ErC10, as determined from the results of the second test with sodium tungstate, was 6.54 mg sodium tungstate/L with 95 % confidence limits of 5.59 and 7.49 mg/L. This value is considered to be more appropriate for estimating a chronic toxicity than the NOEC for this endpoint.

In the second study with sodium tungstate (ABC Laboratories, 2010), conducted at a concentration range of 10.9 to 168 mg/L (mean measured values), showed statistically significant reductions in both yield and growth rate at all test concentrations, with inhibition of growth rate ranging from 23 % at the lowest test concentration to 65 % at the highest test concentration. The NOEC could not be determined, and the ErC50 based upon growth rate was estimated to be 52.9 mg sodium tungstate/L (mean measured concentration).