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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Reference
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:
The rationale to read across the data is attached in Section 13.
Reason / purpose for cross-reference:
read-across source
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
1.7 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
other: Test substance corrected for water content (specified in report as "solids")
Basis for effect:
growth rate
Remarks on result:
other: 95% confidence interval: 1.1-2.5 mg solids/L
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
13 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
other: Test substance corrected for water content (specified in report as "solids")
Basis for effect:
growth rate
Remarks on result:
other: 95% confidence interval: 11-16 mg solids/L
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.23 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
other: Test substance corrected for water content (specified in report as "solids")
Basis for effect:
growth rate
Remarks on result:
other: Based on statistical significance
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.87 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
other: Test substance corrected for water content (specified in report as "solids")
Basis for effect:
growth rate
Remarks on result:
other: Based on biological relevance
Details on results:
- Exponential growth in the control: yes
- Observation of abnormalities: Microscopic observations at the end of the test revealed a normal and healthy appearance of the algal cells exposed to 2.6 mg solids/L when compared to the control.
- Measured concentrations: The initial measured concentrations were 0.90, 2.9, 8.1, 27 and 98 mg solids/L, respectively, in WAFs prepared at loading rates of 1.0, 3.2, 10, 32 and 100 mg solids/L. At the end of the test, the three lowest measured test concentrations had decreased below the LOQ (i.e. 0.01 mg solids/L), while the two highest measured test concentrations were at the level of 54 - 82% of initially measured. Small responses were measured in the analytical blank and in the control samples. The concentrations measured in the control samples at the start of the test and after 24 hours of exposure were comparable to the responses measured in the analytical blank and were considered caused by carry over, hence not relevant. The concentration measured in the control sample at the end of the test was higher than the analytical blank. The reason for this response is unknown. However, since the biological effects in the final test were comparable to the biological effects observed in the combined limit/range-finding test at similar test item concentrations and validity criteria for the control were met, it was assumed that the eventual presence of the test item at the measured concentration during the last phase of the exposure had negligible effect on the algal growth.
- All water quality parameters remained within the requirements as laid down in the study plan throughout the test.
Results with reference substance (positive control):
- Results with reference substance valid? Yes
- EC50 for growth rate inhibition (72h-ErC50) was 0.90 mg/L with a 95% confidence interval ranging from 0.88 to 0.93 mg/L. The historical ranges for growth rate inhibition lie between 0.82 and 2.3 mg/L. The observed 72h-ErC50 for the algal culture tested corresponds with this range.
Reported statistics and error estimates:
Statistical significance: Step-down Jonckheere-Terpstra Test Procedure, α=0.05, one-sided, smaller.
ECx calculation: probit analysis using linear max. likelihood regression with the percentages of growth rate inhibition versus the logarithms of the corresponding TWA concentrations
ToxRat Professional v 3.2.1 (ToxRat Solutions® GmbH, Germany) was used to perform the analysis.

Table 1: Time Weighted Average Versus Loading Rate

Loading rate (mg solids/L)

Measured concentration (mg solids/L)

TWA (mg solids/L)

t=0h

t=24h

t=72 h

Control

0.000078 #

0.000073 #

0.00554

0.00045

1.0

0.900

0.510

0.00025 #

0.23

3.2

2.88

2.26

0.00025 #

0.87

10

8.06

7.63

0.00013 #

2.6

10 *

8.52 *

7.60 *

0.00027 *,#

2.7 #

32

27.2

26.5

14.6

22

100

98.3

76.2

81.0

81

* without algae, # estimated by extrapolation of the calibration curve.

Table 2: Growth Rate and Percentage Inhibition for the Total Test Period


TWA conc.
(mgsolids/L) 

Mean

Std. Dev.

n

%Inhibition

Control

1.854

0.0454

6

 

0.23

1.808

0.0291

3

2.48

0.87

1.807

0.0285

3

2.54*

2.6

1.510

0.0283

3

19*

22

0.764

0.0651

3

59*

81

0.156

0.2699

3

92*

* - effect was statistically significant.

Table 3: Growth Rate and Percentage Inhibition at Different Time Intervals 

TWA conc.

(mgsolids/L)

n

0 – 24 h

24 – 48 h

48 – 72h

Mean

%Inhibition

Mean

%Inhibition

Mean

%Inhibition

Control

6

2.025

 

1.879

 

1.657

 

0.23

3

2.095

-3.4

1.707

9.2

1.623

2.0

0.87

3

2.047

-1.1

1.758

6.5

1.616

2.5

2.6

3

1.714

15

1.450

23

1.367

17

22

3

1.408

30

0.144

92

0.741

55

81

3

1.166

42

-0.940

150

0.241

85

Validity criteria fulfilled:
yes
Remarks:
See 'Overall remarks' for details on validity criteria.
Conclusions:
The ErC10 and ErC50 were 1.7 and 13 mg solids/L, respectively. NOErC was 0.23 mg solids/L based on statistical significance and 0.87 mg solids/L based on biological relevance. This result is read across to Amphoacetates C8.
Executive summary:

In a 72 h toxicity study conducted according to OECD guideline 201 and GLP principles, freshwater algae (Pseudokirchneriella subcapitata) were exposed to individually prepared Water Accommodated Fractions of the test item prepared at nominal loading rates of 1.0, 3.2, 10, 32, and 100 mg solids/L (3 replicates per concentration) and an untreated control (6 replicates). Measured concentrations were not stable throughout the exposure period, therefore Time Weighted Average concentrations were calculated to be 0.23, 0.87, 2.6, 22 and 81 mg solids/L in WAFs prepared at loading rates of 1.0, 3.2, 10, 32 and 100 mg solids/L. A concentration-related increase of growth rate inhibition was observed at all test concentrations. A statistically significant growth rate inhibition was observed at the four highest WAFs tested, but a biologically relevant growth rate inhibition was observed only in the three highest WAFs tested. The EC50 for growth rate inhibition (72h-ErC50) and 72h-ErC10 were 13 and 1.7 mg solids/L, respectively. The 72h-NOErC was 0.23 mg solids/L based on statistical significance and 0.87 mg solids/L based on biological relevance. The study met all validity criteria, and is considered reliable without restriction. This result is read across to Amphoacetates C8.

Description of key information

In a 72 h toxicity study conducted according to OECD guideline 201 and GLP principles, freshwater algae (Pseudokirchneriella subcapitata) were exposed to individually prepared Water Accommodated Fractions of an analogoes substance (C8 -C18 amphoacetates) prepared at nominal loading rates of 1.0, 3.2, 10, 32, and 100 mg solids/L (3 replicates per concentration) and an untreated control (6 replicates). Measured concentrations were not stable throughout the exposure period, therefore Time Weighted Average concentrations were calculated to be 0.23, 0.87, 2.6, 22 and 81 mg solids/L in WAFs prepared at loading rates of 1.0, 3.2, 10, 32 and 100 mg solids/L. A concentration-related increase of growth rate inhibition was observed at all test concentrations. A statistically significant growth rate inhibition was observed at the four highest WAFs tested, but a biologically relevant growth rate inhibition was observed only in the three highest WAFs tested. The EC50 for growth rate inhibition (72h-ErC50) and 72h-ErC10 were 13 and 1.7 mg solids/L, respectively. The 72h-NOErC was 0.23 mg solids/L based on statistical significance and 0.87 mg solids/L based on biological relevance. The study met all validity criteria, and is considered reliable without restriction. This data is read across to the registered substance (rationale attached in Section 13.

Key value for chemical safety assessment

EC50 for freshwater algae:
13 mg/L
EC10 or NOEC for freshwater algae:
1.7 mg/L

Additional information

ErC50: 13 mg/L based on analytically confirmed test substance corrected for water content (and specified in the report as "solids")

ErC10: 1.7 mg/L based on analytically confirmed test substance corrected for water content (and specified in the report as "solids")

NOErC: 0.87 mg/L (biological relevance), based on analytically confirmed test substance corrected for water content (and specified in the report as "solids")