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Toxicity to aquatic plants other than algae

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Reference
Endpoint:
toxicity to aquatic plants other than algae
Type of information:
other: read across from analogue substance
Adequacy of study:
key study
Study period:
2015
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
The test was conducted by means of Read Across approach. The reliability of the source study report is 1. Further information was attached at section 13
Qualifier:
according to guideline
Guideline:
OECD Guideline 221 (Lemna sp. Growth Inhibition Test)
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
Samples were taken from the control and each test group from the bulk test preparation on Day 0 and from the pooled replicates on Day 7. All samples were stored frozen prior to analysis. Duplicate samples were taken at each occasion and stored frozen for further analysis if necessary.
Vehicle:
no
Details on test solutions:
Range-finding test
A nominal amount of test item (154 mg) was dissolved in culture medium and the volume adjusted to 1 liter to give a 100 mg ai/L test concentration from which a series of dilutions was made to give further test concentrations of 10, 1.0 and 0.10 mg ai/L.

Each of the prepared concentrations was inverted several times to ensure adequate mixing and homogeneity.

Definitive Test
A nominal amount of test item (308 mg) was dissolved in culture medium and the volume adjusted to 2 liters to give a 100 mg ai/L test concentration from which a series of dilutions was made to give further test concentrations of 32, 10, 3.2 and 1.0 mg ai/L.

Each of the prepared concentrations was inverted several times to ensure adequate mixing and homogeneity.
Test organisms (species):
Lemna minor
Details on test organisms:
The test was carried out using Lemna minor. A culture of Lemna minor was obtained from Canadian Phycological Culture Centre, University of Waterloo, Ontario, Canada. Cultures were maintained in the laboratory by the periodic replenishment of culture medium. The culture was maintained in the laboratory at a temperature of 24 ± 1 ºC under continuous illumination (intensity approximately 7000 lux) for at least 7 days prior to the start of the test.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
7 d
Test temperature:
The temperature and light intensity in the incubator were recorded daily.
pH:
The pH of each control and test flask was recorded on Day 0 and Day 7.
Nominal and measured concentrations:
Range-finding Test: Nominal test concentrations of 0.10, 1.0, 10 and 100 mg ai/L
Definitive Test: Nominal test concentrations of 1.0, 3.2, 10, 32 and 100 mg ai/L.
Details on test conditions:
Culture Medium
The culture medium used for both the range-finding and definitive tests was the same as that used to maintain the stock culture.

Procedure
Range-finding Test
The test concentrations to be used in the definitive test were determined by a preliminary range-finding test. The range-finding test was conducted by exposing Lemna minor to a series of nominal test concentrations of 0.10, 1.0, 10 and 100 mg ai/L for a period of 7 days. At the request of the Sponsor, all test concentrations were corrected for a test item purity value of 65%.

The test was conducted in glass conical flasks (250 mL). Two replicate flasks were prepared for each control and test concentration. The test item was dissolved directly in culture medium.

A nominal amount of test item (154 mg) was dissolved in culture medium and the volume adjusted to 1 liter to give a 100 mg ai/L test concentration from which a series of dilutions was made to give further test concentrations of 10, 1.0 and 0.10 mg ai/L.

Each of the prepared concentrations was inverted several times to ensure adequate mixing and homogeneity.

The control group was maintained under identical conditions but not exposed to the test item.

At the start of the range-finding test the number of fronds present in each test and control culture was recorded along with observations on frond size, appearance, root length and number of colonies present. The flasks were then incubated at 24 ± 2 ºC under continuous illumination (intensity approximately 7000 lux) on a black, non-reflective surface for 7 days.

On Days 3 and 5 the test solutions were renewed, and observations on the test organisms were recorded on days 3, 5 and 7.

In order to determine the stability of the test item under test conditions a sample of each test concentration was taken for chemical analysis on Day 0 (fresh media) and Day 3 (old media). An additional sample of each test concentration was prepared on Day 0 and incubated alongside the test until Day 7 in order to determine stability over the entire test duration. All samples were stored frozen prior to analysis.


Definitive Test
Based on the results of the range-finding test the following test concentrations were assigned to the definitive test: 1.0, 3.2, 10, 32 and 100 mg ai/L.


Experimental Preparation
A nominal amount of test item (308 mg) was dissolved in culture medium and the volume adjusted to 2 liters to give a 100 mg ai/L test concentration from which a series of dilutions was made to give further test concentrations of 32, 10, 3.2 and 1.0 mg ai/L.

Each of the prepared concentrations was inverted several times to ensure adequate mixing and homogeneity.

The concentration and stability of the test item in the test preparations were verified by chemical analysis on Day 0 and Day7.


Exposure Conditions
As in the range-finding test glass conical flasks were used. Three flasks each containing 250 mL of solution were prepared for the control and each treatment group.

The control group was maintained under identical conditions but not exposed to the test item.

Each control and test flask was inoculated with 3 colonies of Lemna minor (total 9 fronds). The flasks were then incubated at 24 ± 2 ºC under constant illumination (intensity approximately 7000 lux) on a black, non-reflective surface for 7 days.
A static testing regime was employed.


Evaluations
Test Organism Observations
The number of fronds present in each test and control culture was recorded on days 0, 3, 5 and 7 along with observations on frond size, appearance, root length and number of colonies present.

In addition the dry weight of the fronds in each control and treatment group was determined on day 7. At the start of the test six replicate samples of fronds identical to those used to inoculate the test vessels were taken and the dry weight determined. At the end of the test the dry weight of colonies from each control and test vessel was determined by blotting the colonies dry and drying at 60 °C to constant weight.


Data Analysis
Doubling Time
The doubling time (Td) of frond number, and hence performance of the test against the validation criterion of doubling time, was calculated for the control vessels using the following formula:

Td = ln 2/µ

Where:
µ = the average specific growth rate for the control vessels.


Response Variables
In order that the test results are acceptable to regulatory authorities worldwide, the effects on the growth of Lemna were evaluated using both response variables (a) and (b) described below:

a) Average specific growth rate: this response variable was calculated on the basis of changes in the logarithms of frond numbers, and in addition, on the basis of changes in the logarithms of dry weight over time (expressed per day) in the controls and each treatment group.

b) Yield: this response variable was calculated on the basis of changes in frond number, and in addition, on the basis of changes in dry weight in the controls and in each treatment group until the end of the test.

It should be noted that toxicity values calculated using these two response variables are not comparable and the difference must be recognized when using the results of the test. ECx values based upon average specific growth rate (ErCx) will be higher than results based upon yield (EyCx) under the test conditions of this Guideline, due to the underlying mathematics of the respective approaches. This is not to be interpreted as a difference in sensitivity between the response variables: simply the values are different mathematically. The concept of average specific growth rate is based upon the general exponential growth pattern of Lemna in non-limited cultures. Toxicity is estimated on the basis of the effects on the growth rate without being dependent on the absolute level of the specific growth rate of the control, slope of the concentration-response curve or on test duration. Results based upon yield are dependent upon all these variables.


Average Specific Growth Rate
The average specific growth rate for a specific period was calculated as the logarithmic increase in the growth variables -frond numbers and dry weight - using the formula below for each replicate of the control and treatment groups:

µi-j = (1n(Nj) – 1n(Ni)) / t

Where:
µi-j = average specific growth rate from time i to j
Ni = number of fronds or dry weight in the test or control vessel at time i
Nj = number of fronds or dry weight in the test or control vessel at time j
t = time period from i to j

For each control and treatment group the mean value for growth rate along with the standard deviation was calculated.
Percentage inhibition of growth rate (Ir) was calculated as follows:

%Ir = ((µc - µt) / µc) x 100

Where:
% Ir = percentage inhibition of average specific growth rate
µc = mean value of µ for the control
µt = mean value of µ for the treatment group


Yield
Effects on yield were determined on the basis of frond numbers and dry weight present in each test vessel at the start and end of the test. For dry weight, the starting biomass was determined on the basis of a sample of fronds taken from the same batch used to inoculate the test vessels. For each test concentration and control, the mean value for yield along with variance estimates was calculated.

Percentage inhibition in yield (Iy) was calculated for each treatment group as follows:

%Iy = ((bc – bt) / bc) x 100

Where:
% Iy = percentage reduction in yield
bc = final biomass minus starting biomass for the control group
bt = final biomass minus starting biomass for the treatment group


Determination of ECx Values
Percentage inhibition (arithmetic axis) was plotted against test concentration (logarithmic axis) and a line fitted by computerized interpolation using the Xlfit software package (IDBS). ECx values were then determined from the equation for the fitted line.

It was not possible to calculate 95% confidence limits for the EC50 values as the data generated did not fit the models available for the calculation of confidence limits.


Geometric Mean Measured Test Concentrations
The geometric mean measured test concentrations of the samples were calculated as follows using the measured test concentrations of replicates R1 - R3 pooled:

GM = √(C0 x C1)

Where:
GM = geometric mean measured test concentration (mg ai/L)
C0 = measured concentration at the start of the test (mg ai/L)
C1 = measured concentration at the end of the test (mg ai/L)
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Duration:
7 d
Dose descriptor:
EC50
Effect conc.:
82 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
act. ingr.
Basis for effect:
frond number
Duration:
7 d
Dose descriptor:
EC50
Effect conc.:
50 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
act. ingr.
Basis for effect:
other: Dry weight Average specific growth rate
Duration:
7 d
Dose descriptor:
NOEC
Effect conc.:
0.64 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
act. ingr.
Basis for effect:
frond number
Duration:
7 d
Dose descriptor:
LOEC
Effect conc.:
2.3 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
act. ingr.
Basis for effect:
frond number
Duration:
7 d
Dose descriptor:
EC50
Effect conc.:
17 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
act. ingr.
Basis for effect:
frond number
Duration:
7 d
Dose descriptor:
EC50
Effect conc.:
13 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
act. ingr.
Basis for effect:
other: Dry weight Yield
Details on results:
Range-finding Test
The results showed no significant effect on growth at the test concentrations of 0.10 and 1.0 mg ai/L. However, growth was observed to be reduced at 10 and 100 mg ai/L.

Based on this information test concentrations of 1.0, 3.2, 10, 32 and 100 mg ai/L were selected for the definitive test.

Chemical analysis of the test preparations on Day 0 showed measured test concentrations to range from 78% to 94% of nominal. A slight decline in measured test concentrations was observed on Day 3 in the range of 68 % to 94 % of nominal, and on Day 7 in the range of 70 % to 89 % of nominal.


Growth Data Based on Frond Number
Accordingly the following results based on inhibition of average specific growth rate and yield were determined from the frond number data:

Average Specific Growth Rate
ErC10 (frond number) = 3.5 mg ai/L
ErC20 (frond number) = 11 mg ai/L
ErC50 (frond number) = 82 mg ai/L

Where:

ErCx = the test concentration that reduced average specific growth rate by x%.

Statistical analysis of the average specific growth rate data was carried out for the control and all test concentrations using one way analysis of variance incorporating Bartlett's test for homogeneity of variance (Sokal and Rohlf 1981) and Dunnett's multiple comparison procedure for comparing several treatments with a control (Dunnett 1955). There were no statistically significant differences between the control and 0.64 mg ai/L test concentration (P≥0.05), however all other test concentrations were significantly different (P<0.05) and, therefore the "No Observed Effect Concentration" (NOEC) in terms of inhibition of average specific growth rates calculated from frond numbers was 0.64 mg ai/L. Correspondingly the “Lowest Observed Effect Concentration” (LOEC) was determined to be 2.3 mg ai/L.


Yield
EyC10 (frond number) = 0.63 mg ai/L
EyC20 (frond number) = 2.1 mg ai/L
EyC50 (frond number) = 17 mg ai/L

Where:

EyCx = the test concentration that reduced yield by x %.

Statistical analysis of the yield data was carried out for the control and all test concentrations using one way analysis of variance incorporating Bartlett's test for homogeneity of variance (Sokal and Rohlf 1981) and Dunnett's multiple comparison procedure for comparing several treatments with a control (Dunnett 1955). There were no statistically significant differences between the control and 0.64 mg ai/L test concentration (P≥0.05), however all other test concentrations were significantly different (P<0.05) and, therefore the "No Observed Effect Concentration" (NOEC) in terms of inhibition of yield calculated from frond numbers was 0.64 mg ai/L. Correspondingly the “Lowest Observed Effect Concentration” (LOEC) was determined to be 2.3 mg ai/L.


Growth Data Based on Dry Weight
Accordingly the following results based on inhibition of average specific growth rate and yield were determined from the dry weight data:


Average Specific Growth Rate
ErC10 (dry weight) = 1.8 mg ai/L
ErC20 (dry weight) = 6.1 mg ai/L
ErC50 (dry weight) = 50 mg ai/L

Where:

ErCx = the test concentration that reduced average specific growth rate by x %.

Statistical analysis of the average specific growth rate data was carried out for the control and all test concentrations using one way analysis of variance incorporating Bartlett's test for homogeneity of variance (Sokal and Rohlf, 1981) and Dunnett's multiple comparison procedure for comparing several treatments with a control (Dunnett, 1955). There were no statistically significant differences between the control and 0.64 mg ai/L test concentration (P≥0.05), however all other test concentrations were significantly different (P<0.05) and, therefore the "No Observed Effect Concentration" (NOEC) in terms of inhibition of average specific growth rate calculated from dry weight was 0.64 mg ai/L. Correspondingly the “Lowest Observed Effect Concentration” (LOEC) was determined to be 2.3 mg ai/L.


Yield
EyC10 (dry weight) = 0.58 mg ai/L
EyC20 (dry weight) = 1.8 mg ai/L
EyC50 (dry weight) = 13 mg ai/L

Where:

EyCx = the test concentration that reduced yield by x%.

Statistical analysis of the yield data was carried out for the control and all test concentrations using one way analysis of variance incorporating Bartlett's test for homogeneity of variance (Sokal and Rohlf 1981) and Dunnett's multiple comparison procedure for comparing several treatments with a control (Dunnett 1955). There were no statistically significant differences between the control and 0.64 mg ai/L test concentration (P≥0.05), however all other test concentrations were significantly different (P<0.05) and, therefore the "No Observed Effect Concentration" (NOEC) in terms of inhibition of yield calculated from dry weight was 0.64 mg ai/L. Correspondingly the “Lowest Observed Effect Concentration” (LOEC) was determined to be 2.3 mg ai/L.
Results with reference substance (positive control):
A positive control (Harlan Study Number 41403075) used 3,5-dichlorophenol as the reference item at concentrations of 0.625, 1.25, 2.5, 5.0 and 10 mg/L.

Exposure conditions and data evaluation for the positive control were similar to those in the definitive test.

Exposure of Lemna minor to the reference item gave the following results:
The average specific growth rate (frond number) EC50 was 3.4 mg/L with 95 % confidence limits of 3.1 - 3.6 mg/L. The NOEC was 2.5 mg/L and the LOEC was 5.0 mg/L.
The average specific growth rate (dry weight) EC50 was 3.4 mg/L with 95 % confidence limits of 3.2 - 3.7 mg/L. The NOEC was 1.25 mg/L and the LOEC was 2.5 mg/L.
The yield (frond number) EC50 was 2.6 mg/L with 95 % confidence limits of 2.4 - 2.9 mg/L. The NOEC was 2.5 mg/L and the LOEC was 5.0 mg/L.
The yield (dry weight) EC50 was 2.7 mg/L with 95 % confidence limits of 2.5 - 2.9 mg/L. The NOEC was 1.25 mg/L and the LOEC was 2.5 mg/L.

The results from the positive control with 3,5-dichlorophenol were within the normal ranges for this reference item.
Reported statistics and error estimates:
One way analysis of variance incorporating Bartlett's test for homogeneity of variance (Sokal and Rohlf, 1981), and Dunnett's multiple comparison procedure for comparing several treatments with a control (Dunnett, 1955), were carried out on the average specific growth rate and yield data at 7 days for the control and all test concentrations to determine any statistically significant differences between the test and control groups. All statistical analyses were performed using the SAS computer software package (SAS, 1999-2001).

Verification of Test Concentrations

Chemical analysis of the test preparations on Day 0 (fresh media) showed measured test concentrations to range from 0.90 to 95 mg ai/L. A slight decline in measured test concentration was observed on Day 7 in the range of 0.46 to 88 mg ai/L.

 

Current regulatory advice is that in cases where a decline in measured concentrations is observed, geometric mean measured concentrations should be used for calculating EC50values. It was therefore considered justifiable to base the results on the geometric mean measured test concentrations in order to give a “worst case” analysis of the data. The geometric mean measured test concentrations were determined to be:

 

Nominal Test Concentration
(mg ai/L)

Geometric Mean Measured Test Concentration (mg ai/L)

Expressed as a % of the Nominal Test Concentration

1.0

0.64

64

3.2

2.3

72

10

9.1

91

32

30

94

100

91

91

Validation Criteria

The following data show that the doubling time of the control cultures was 1.76 days in line with the OECD Guideline that states the doubling time should be less than 2.5 days:

 

Mean frond number in control cultures at day 0: 9

Mean frond number in control cultures at day 7: 99

Water Quality Criteria

Temperature was maintained at 24 ± 2 ºC throughout the test.

Frond Numbers and Percentage Inhibition of Growth from the Range-finding Test

Nominal Concentration

(mg ai/L)

Number of Fronds

Average Specific Growth Rate

Yield

Day 0

Day 3

Day 5

Day 7

(0 – 7 Day)

% Inhibition

(0 – 7 Day)

% Inhibition

Control

R1

9

24

49

112

0.360

-

103

-

R2

9

29

65

146

0.398

137

Mean

9

27

57

129

0.379

120

0.10

R1

9

30

66

138

0.390

[3]

129

[9]

R2

9

27

62

141

0.393

132

Mean

9

29

64

140

0.392

131

1.0

R1

9

28

62

132

0.384

0

123

2

R2

9

28

63

121

0.371

112

Mean

9

28

63

127

0.378

118

10

R1

9

24

39

87

0.324

17

78

39

R2

9

24

40

76

0.305

67

Mean

9

24

40

82

0.315

73

100

R1

9

21

23

43

0.223

38

34

68

R2

9

23

32

50

0.245

41

Mean

9

22

28

47

0.234

38

R1– R2= Replicates 1 and 2

Frond Numbers from the Definitive Test

Nominal Concentration

(mg ai/L)

Number of Fronds

Day 0

Day 3

Day 5

Day 7

Control

R1

9

23

51

113

R2

9

24

49

93

R3

9

23

46

92

Mean

9

23

49

99

1.0

R1

9

21

38

89

R2

9

19

42

96

R3

9

20

41

99

Mean

9

20

40

95

3.2

R1

9

20

37

70

R2

9

21

36

67

R3

9

20

40

82

Mean

9

20

38

73

10

R1

9

21

33

63

R2

9

19

35

64

R3

9

22

36

65

Mean

9

21

35

64

32

R1

9

20

34

48

R2

9

21

31

49

R3

9

20

32

55

Mean

9

20

32

51

100

R1

9

14

22

25

R2

9

21

25

29

R3

9

14

17

25

Mean

9

16

21

26

R1– R3= Replicates 1 to 3

Inhibition of Average Specific Growth Rate and Yield Based on Frond Numbers

Nominal Concentration
(mg ai/L)

Average Specific Growth Rate

Yield

(0 – 7 Day)

% Inhibition

(0 – 7 Day)

% Inhibition

Control

Mean

0.342

-

90

-

SD

0.016

12

1.0

Mean

0.336

2

86

4

SD

0.008

5

3.2

Mean

0.299

13

64

29

SD

0.015

8

10

Mean

0.280

18

55

39

SD

0.002

1

32

Mean

0.247

28

42

53

SD

0.011

4

100

Mean

0.153

55

17

81

SD

0.012

2

SD– Standard Deviation

Dry Weights from the Definitive Test

Nominal Concentration

(mg ai/L)

Dry Weight (mg)

Day 0*

Day 7

Control

R1

 

8.6

R2

 

8.4

R3

 

8.1

Mean

1.2

8.4

1.0

R1

 

8.2

R2

 

8.5

R3

 

8.3

Mean

1.2

8.3

3.2

R1

 

5.6

R2

 

6.0

R3

 

7.2

Mean

1.2

6.3

10

R1

 

5.1

R2

 

4.7

R3

 

5.1

Mean

1.2

5.0

32

R1

 

4.2

R2

 

3.6

R3

 

4.3

Mean

1.2

4.0

100

R1

 

2.3

R2

 

3.1

R3

 

2.4

Mean

1.2

2.6

*Mean value determined from 6 replicate weighings

R1– R3= Replicates 1 to 3

Inhibition of Average Specific Growth Rate and Yield Based on Dry Weight

Nominal Concentration
(mg ai/L)

Average Specific Growth Rate

Yield

(0 – 7 Day)

% Inhibition

(0 – 7 Day)

% Inhibition

Control

Mean

0.277

-

7.2

-

SD

0.004

0.3

1.0

Mean

0.277

0

7.1

1

SD

0.003

0.2

3.2

Mean

0.235

15

5.1

29

SD

0.019

0.8

10

Mean

0.203

27

3.8

47

SD

0.007

0.2

32

Mean

0.173

38

2.8

61

SD

0.014

0.4

100

Mean

0.109

61

1.4

81

SD

0.023

0.4

SD– Standard Deviation

pH Values in the Definitive Test

Nominal Concentration

(mg ai/L)

Time (Days)

0

7

Control

R1

6.9

8.2

R2

6.9

8.1

R3

6.9

8.0

1.0

R1

6.8

7.9

R2

6.8

7.8

R3

6.8

7.8

3.2

R1

6.8

7.6

R2

6.8

7.5

R3

6.8

7.5

10

R1

6.8

7.5

R2

6.9

7.5

R3

6.9

7.5

32

R1

6.9

7.4

R2

7.0

7.4

R3

7.0

7.4

100

R1

7.0

7.4

R2

7.0

7.4

R3

7.0

7.3

R1– R3= Replicates 1 to 3

Exposure of Lemna minor to the test item based on the geometric mean measured test concentrations gave the following results:

 

Response Variable

Measurement Variable

EC50

(mg ai/L)

No Observed Effect Concentration (NOEC) (mg ai/L)

Lowest Observed Effect Concentration (LOEC) (mg ai/L)

Average Specific Growth Rate

Frond Number

82

0.64

2.3

Dry Weight

50

0.64

2.3

Yield

Frond Number

17

0.64

2.3

Dry Weight

13

0.64

2.3

 

Validity criteria fulfilled:
yes
Conclusions:
The effect of the test item on the growth of Lemna minor has been investigated over a 7-day period and gave the following results based on the geometric mean measured test concentrations:
The average specific growth rate (frond number) EC50 was 82 mg/l
The average specific growth rate (dry weight) EC50 was 50 mg/l
Executive summary:

Method

A study was performed to assess the effect of the test item on the growth of the freshwater plant Lemna minor. The method followed that described in the OECD Guideline No. 221 “Lemna Growth Inhibition Test (March 2006)”.

 

Following a preliminary range-finding test, Lemna minor was exposed to an aqueous solution of the test item at nominal concentrations of 1.0, 3.2, 10, 32 and 100 mg active ingredient (ai)/L (three replicate flasks per concentration) for a period of 7 days, under constant illumination at a temperature of 24 ± 2°C. 

 

The number of fronds in each control and treatment group was recorded on days 0, 3, 5 and 7 along with observations on plant development.

….

Observations

Chemical analysis of the test preparations on Day 0 (fresh media) showed measured test concentrations to range from 0.90 to 95 mg ai/L. A slight decline in measured test concentration was observed on Day 7 in the range of 0.46 to 88 mg ai/L.

 

Given this decline in measured test concentrations it was considered justifiable to base the results on the geometric mean measured test concentrations in order to give a “worst case” analysis of the data.

Results

The average specific growth rate (frond number) EC50 was 82 mg/l

The average specific growth rate (dry weight) EC50 was 50 mg/l.

The yield (frond number) EC50 was 17 mg/l.

The yield (dry weight) EC50 was 13 mg/l.

The NOEC was 0.64 mg/L and the LOEC was 2.3 mg/l.

Description of key information

ErC50 = 82 mg/l (frond number)

ErC50 = 50 mg/l (dry weight)

Key value for chemical safety assessment

EC50 for freshwater plants:
50 mg/L

Additional information

No studies on the "Short-term toxicity to aquatic invertebrates" are available for the substance in itself.

Nevertheless a study have been conducted with an analogue molecule (Similar Substance 01). Further information are reported in the Read Across justification attached to section 13.

A study was performed to assess the effect of the Similar Substance 01 on the growth of the freshwater plant Lemna minor according to the OECD Guideline No. 221.

Following a preliminary range-finding test,Lemna minorwas exposed to an aqueous solution of the test item at nominal concentrations of 1.0, 3.2, 10, 32 and 100 mg active ingredient (a.i.)/l.

The number of fronds in each control and treatment group was recorded on days 0, 3, 5 and 7 along with observations on plant development. 

Chemical analysis of the test preparations on Day 0 (fresh media) showed measured test concentrations to range from 0.90 to 95 mg/l. A slight decline in measured test concentration was observed on Day 7 in the range of 0.46 to 88 mg/l.

Given this decline in measured test concentrations it was considered justifiable to base the results on the geometric mean measured test concentrations in order to give a “worst case” analysis of the data. 

Exposure ofLemna minorto the test item based on the geometric mean measured test concentrations gave the following results: 

The average specific growth rate (frond number) EC50 was 82 mg ai/L.

The average specific growth rate (dry weight) EC50 was 50 mg ai/L.

The yield (frond number) EC50 was 17 mg ai/L.

The yield (dry weight) EC50 was 13 mg ai/L.

The NOEC was 0.64 mg/L and the LOEC was 2.3 mg ai/L.