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Toxicity to aquatic plants other than algae

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Description of key information

According to OECD guideline 221 performed with Lemna gibba, the following key values were determined based on frond number after an exposure period of 7 days: ErC50 = 66.414 mg/L and ErC10 = 0.046 mg/L.

Key value for chemical safety assessment

EC50 for freshwater plants:
66.414 mg/L
EC10 or NOEC for freshwater plants:
0.046 mg/L

Additional information

The growth of Lemna gibba exposed to the test item was investigated in a 7 day static test to determine the test item concentrations causing 10, 20 and 50% inhibition of growth rate (r) and yield (y). The test was performed in glass beakers containing 400 mL of each treatment per replicate. Seven test item concentrations of 0.032, 0.16, 0.8, 4.0, 20, 100 and 500 mg/L plus the control were used in the test. The concentrations of the test item were determined with a validated spectrophotometric method. Samples of each test item concentration and the control were collected at exposure initiation and at exposure termination. The test item concentrations determined in samples collected at exposure initiation were in the range of 84.3 – 95.5% of the nominal concentration. Therefore, the results confirm correct preparation of the test item concentrations. The test item concentrations determined in samples collected at exposure termination were in the range of 81.4 – 101.1% of the nominal concentration. Therefore, the test item concentrations were stable under static test conditions. The endpoint values were determined on the basis of the nominal test item concentrations. At exposure termination, in the test item concentrations of 0.032, 0.16 and 0.8 mg/L no distinctive changes from the normal development of plants in the control were observed. In the test item concentration of 4.0 mg/L fronds were slightly bent down. In the test item concentration of 20, 100 and 500 mg/L,shorter roots were observed. In the test item concentrations of 100 and 500 mg/L spots of chlorosis or necrosis on fronds were observed. Moreover, in the test item concentrations of 20 and 100 mg/L bent down fronds were observed, in the test item concentration of 500 mg/L break up of colonies was observed. The endpoint values based on nominal test item concentrations are given below:

 

Based on frond number:

ErC50/7d: is 66.414 mg/L (95% confidence limits 29.835 – 193.167)

ErC20/7d: is 0.556 mg/L (95% confidence limits 0.109 – 1.549)

ErC10/7d: is 0.046 mg/L (95% confidence limits 0.004 – 0.201)

EyC50/7d: is 1.407 mg/L (95% confidence limits 0.447 – 3.993)

EyC20/7d: is 0.043 mg/L (95% confidence limits 0.003 – 0.170)

EyC10/7d: is lower than 0.032 mg/L

 

Based on dry weight:

ErC50/7d: is 42.863 mg/L (95% confidence limits 22.347 – 93.041)

ErC20/7d: is 1.048 mg/L (95% confidence limits 0.283 – 2.462)

ErC10/7d: is 0.151 mg/L (95% confidence limits 0.022 – 0.491)

EyC50/7d: is 1.341 mg/L (95% confidence limits 0.579 – 3.017)

EyC20/7d: is 0.097 mg/L (95% confidence limits 0.015 – 0.262)

EyC10/7d: is lower than 0.032 mg/L

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