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Diss Factsheets

Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

The comparison of the results for the parameter of concern for PART I and II of the study showed no dose response relationship. Therefore it is demonstrated that the observed difference exceeding the 10% level is due to test design depending data variability. Based on this arguments the inhibition of growth observed in this study is due to algistatic effects caused by light absorption only.

Key value for chemical safety assessment

Additional information

A study was performed to assess the adverse effects of test substance on the growth and growth rate of the planktonic freshwater algal species Desmodesmus subspicatus over several generations. The study was conducted in accordance with EU Method C.3., OECD Guideline 201 and an instruction for the performance of a modified algal growth inhibition test published by Memmert & Knoell.

Exponentially growing algal cells were exposed for a period of 72 hours to a range of concentrations, nominally 0.4, 1.0, 2.1, 4.6, 10.3, 22.7 and 50 mg/L of test substance dissolved in water (PART I). A second series (PART II) of test vessels treated in the same way as the controls, but placed below glass vessels containing the same range of concentrations of the test substance as described above, but without algae, was set up to distinguish between algistatic (indirect effect caused by light absorption) and algicide (toxic) effects.The cell densities were measured at 24 h intervals. Inhibition of the algal population was measured as reduction in growth (index b) and growth rate (index r), relative to control.

All results are expressed in terms of nominal concentrations. Measured concentrations ranged from 83 - 101 % of nominal values at 0 h, and from 76 - 88 % of nominal values at 72 h, respectively.

 

Results [mg/L]:

PART I

PART II

EbC 50 (0-72h)

3.6

5.6

ErC 50 (0-72h)

14

14

NOEC [b]

0.4

2.1

LOEC [b]

1.0

4.6

NOEC [r]

2.1

2.1

LOEC [r]

4.6

4.6

A comparison of the results for the parameter "percentage inhibition of the growth rate" gained in PART I and II of the study results in no differences exceeding 10% with the exception of the results for the concentration 1 mg/L. For this concentration a difference of 13.5% between the "percentage inhibition of the growth rate" for PART I and II of the study was estimated. This value is caused by an increased algae growth in the test substance concentration 1 mg/L (PART II) compared to the control.

The comparison of the results for the parameter of concern for PART I and II of the study showed no dose response relationship. Therefore it is demonstrated that the observed difference exceeding the 10% level is due to test design depending data variability. Based on this arguments the inhibition of growth observed in this study is due to algistatic effects caused by light absorption only.