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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The toxicity of C36-alkylenediamines to algae was tested according to OECD guideline 201. The ErL50 was observed to be 0.922 mg a.i./L and the NOEL was observed to be 0.32 mg a.i./L. Considering the strong sorption of the test substance to algae and the limited measured sorption to glassware at the end of the test (± 10%) the endpoints are in agreement with OECD guideline 201 point 40 based on the measured initial concentrations: ErC50 = 44.3 µg/L and ErC10 = 11.7 µg/L based on active ingredient concentrations.

Key value for chemical safety assessment

EC50 for freshwater algae:
44.3 µg/L
EC10 or NOEC for freshwater algae:
11.7 µg/L

Additional information

The effects of C36 -alkylenediamines (CAS no 68955 -56 -6) on the growth of the freshwater green alga Pseudokirchneriella subcapitata were tested according to OECD TG 201.

The test substance is poorly soluble in water and therefore water accommodated fractions (WAF) were prepared. The test substance is stable under test conditions. Each loading concentration and the control were analytically verified at the beginning and the end of the test in parallel test vessels via LC-MS/MS analysis. In addition the fraction sorbed to glassware was quantified at the end of the test. Sorption to glassware occurs immediately after preparation of the test solutions meaning that glassware was already largely saturated when taking the T0 samples. For the quantification of the test item the two main product peaks selected. These peaks correspond with the masses of 533 g/mol and 535 g/mol.

Results of the specific chemical analysis

Nominal test substance conc.

[mg/L]

Meas. conc. T0

[µg/L]

Meas. conc. T72

[µg/L]

Meas. conc.

sorbed

[µg/L]

Control

< LOQ

< LOQ

< 0.15

0.01

0.381

0.128

< 0.15

0.032

0.611

0.274

< 0.15

0.1

3.29

1.16

0.377

0.32

11.1

3.38

2.52

1.00

51.3

5.60

5.03

From the results of the chemical analysis it can be observed that only a small fraction of the nominal loading is dissolved at the start of the test and that up to almost 90% of the initial observed concentration is again lost during the test via sorption to glassware (in the parallel sample). That sorption to glassware in the actual test vessels is however about 12% which means that a large fraction must be adsorbed to algae.

Endpoints concentrations should preferentially be expressed as measured values to analytically confirm the exposure concentration to the test organism during the study. If a test substance is expected to be stable (>80% of nominal) during the test a high and a low concentration at the start of the test may be taken for chemical analysis and nominal concentrations may be used if stability is confirmed. All concentrations at the start and at the end of the test should be analyzed if it is expected that the concentration will not remain within 80-100% of the nominal concentrations. Calculation of the exposure concentration should then be calculated as a geometric mean of the measured concentrations at the beginning and at the end of the test as far as is possible and appropriate. If the test chemical cannot be quantified at the concentrations causing effects, the effect concentration may be based on nominal concentration. Measured concentrations are preferred however. In the case of algae tests conducted with adsorbing substances the relevant OECD guideline (Ref 1 paragraph 40) acknowledges that quantification such substances particularly when low concentrations are concerned quantification at the end of the study can be difficult. In such cases use of measured initial concentrations is considered acceptable.

For this reason it is considered justified to use the measured initial concentration to base the dose response on and not the mean measured concentration as most of the measured initial test substance concentration is actually either sorbed to algae or in the test solution. The following Key values for the chemical safety assessment can therefore be derived: ErC50 of 44.3 µg/L and ErC10 of 11.7 µg/L based on active ingredient concentration.

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