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Short-term toxicity to aquatic invertebrates

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Description of key information

Key study performed according to GLP and OECD Guideline 202:
The acute toxicity of the test item to the freshwater invertebrate Daphnia magna has been investigated. Given the decline in measured test concentrations it was considered justifiable to base the results on the time-weighted mean measured test concentrations.The 48-Hour EC50 value based on time-weighted mean measured test concentrations of 0.80 mg/L with 95% confidence limits of 0.68 – 0.94 mg/L. The Lowest Observed Effect Concentration was considered to be 0.73 mg/L. The No Observed Effect Concentration at 48 hours was 0.33 mg/L.

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
0.8 mg/L

Additional information

Introduction

A study was performed to assess the acute toxicity of 9-decenoic acid, methyl ester (purity 99 %) to Daphnia magna. The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals (April 2004) No 202, "Daphnia sp., Acute Immobilisation Test" referenced as Method C.2 of Commission Regulation (EC) No. 440/2008 and the US EPA Draft Ecological Effects Test Guidelines OPPTS 850.1010 "Aquatic Invertebrate Acute Toxicity Test, Freshwater Daphnids".

 

Methods

In the range-finding test, 10 daphnids were exposed to a series of nominal test concentrations of 0.10, 1.0, 10 and 100% v/v saturated solution for a period of 48 hours at a temperature of 20 °C to 21 °C under static conditions. The number of immobilized Daphnia was recorded after 24 and 48 h.

In the definitive test, 20 daphnids (4 replicates of 5 animals) were exposed to an aqueous solution of the test item at nominal concentrations of 1.0, 1.8, 3.2, 5.6, 10, 18, 32, 56 and 100% v/v saturated solution for 48 hours at a temperature of 21°C to 22°C and pH 7.7- 8.0 under semi-static test conditions. The test item solution was prepared by stirring an excess (50 mg/L) of test item in test medium using a propeller stirrer at approximately 1500 rpm for 24 h. After the stirring period any undissolved test item was removed by filtration (0.2 μm Gelman AcroCap filter, first approximate 500 mL discarded in order to pre-condition the filter) to produce a 100 % v/v saturated solution of the test item. Media preparation trials conducted using a similar method of preparation indicated a water solubility value of approximately 22 mg/L when using this method of preparation. Dilutions of the 100% v/v saturated solution were prepared in test medium to give the remainder of the test series. The number of immobilized Daphnia was recorded after 24 and 48 h.

Results

In the range-finding test, no immobilization was observed at the test concentrations 0.10 and 1.0 % v/v saturated solution. However, immobilization was observed at 10 and 100 % v/v saturated solution. Therefore, test concentrations of 1.0, 1.8, 2.0, 5.6, 10, 18, 32, 56 and 100 % v/v saturated solution were selected for the definitive test.

In the definitive test the 48-Hour EC50 for the test item to Daphnia magna based on time-weighted mean measured test concentrations was 0.80 mg/L with 95 % confidence limits of 0.68 – 0.94 mg/L. The Lowest Observed Effect Concentration was considered to be 0.73 mg/L. The No Observed Effect Concentration was 0.33 mg/L.

In the definitive test, chemical analysis was conducted on the test concentrations at the No Observed Effect Concentration (NOEC) and above. Analysis of the 5.6 to 100 % v/v saturated solution test concentrations at 0 hours showed measured concentrations to range from 0.832 to 19.7 mg/L. Analysis of the corresponding old media samples at 24 h showed measured concentrations to range from less than the limit of quantitation (LOQ) of the analytical method (assessed as 0.087 mg/L) to 11.3 mg/L. At 24 h the 32 to 100 % v/v saturated solution test concentrations were not renewed due to 100 % immobilization after 24 h exposure. Analysis of the freshly prepared media for the 5.6 to 18 % v/v saturated solution test concentrations at 24 h showed measured concentrations to range from 0.717 to 2.78 mg/L whilst analysis of the corresponding old media at 48 h showed measured concentrations to range from 0.178 to 0.519 mg/L.

Given the decline in measured test concentrations over each 24-Hour period it was considered justifiable to base the results on the time-weighted mean measured test concentrations. The time-weighted mean measured test concentrations were calculated as follows. Where a measured concentration of less than the limit of quantitation (LOQ) of the analytical method was determined, a value of 1/2 the LOQ was substituted into the equation:

Area= ((C0 -C1)/ lnC0 -lnC1)) x days

TWM= Total area/ Total number of days of the test

Where Area= are under the exponential curve for each renewal period, C0= measured concentration at the start of each renewal period (mg/L), C1= measured concentration at the end of each renewal period (mg/L), Days= number of days in the renewal period, TWM= time-weighted mean measured test concentration (mg/L).

The time-weighted mean measured test concentrations were calculated to be 0.33, 0.73, 1.5, 3.8, 7.6 and 15 mg/L.

Cumulative Immobilization Data in the Definitive Test:

Nominal Concentration (% v/v Saturated Solution)

Time-Weighted Mean Measured Concentration

(mg/L)

Cumulative Immobilized Daphnia
(Initial Population: 5 Per Replicate)

24 Hours

48 Hours

R1

R2

R3

R4

Total

%

R1

R2

R3

R4

Total

%

Control

Control

0

0

0

0

0

0

0

0

0

0

0

0

1.0

-

0

0

0

0

0

0

0

0

0

0

0

0

1.8

-

0

0

0

0

0

0

0

0

0

1*

1*

5*

3.2

-

0

0

0

0

0

0

0

0

0

0

0

0

5.6

0.33

0

0

0

0

0

0

0

0

0

0

0

0

10

0.73

1

2

0

2

5

25

1

2

2

2

7

35

18

1.5

4

4

3

3

14

70

5

5

5

5

20

100

32

3.8

5

5

5

5

20

100

5

5

5

5

20

100

56

7.6

5

5

5

5

20

100

5

5

5

5

20

100

100

15

5

5

5

5

20

100

5

5

5

5

20

100

R1– R4= Replicates 1 to 4

- Not applicable as no chemical analysis performed

* Considered to be due to natural causes rather than a toxic effect given that less than 10% immobilization occurred at this concentration and no immobilization was observed at the higher test concentrations of 3.2 and 5.6% v/v saturated solution.