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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

Two toxicity studies on algal are available (one freshwater study in Pseudokirchneriella subcapitata and one marine study in Skeletonema costatum).
In the freshwater study the 72 hr LC50 (growth rate) was found to be >100 mg ai/l and the NOEC 10 mg ai/l.
In the marine study the 72 hr LC50 (growth rate) was found to be 1204 mg/l and the NOEC 320 mg/l.

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L
EC50 for marine water algae:
1 204 mg/L
EC10 or NOEC for freshwater algae:
10 mg/L
EC10 or NOEC for marine water algae:
320 mg/L

Additional information

Freshwater study (Vryenhoef H (2012))

A study was performed to assess the effect of the test item on the growth of the green alga Pseudokirchneriella subcapitata. The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" referenced as Method C.3 of Commission Regulation (EC) No 440/2008.

Following a preliminary range-finding test, Pseudokirchneriella subcapitata was exposed to an aqueous solution of the test item at concentrations of 1.0, 3.2, 10, 32 and 100 mg active ingredient (ai)/l (three replicate flasks per concentration) for 72 hours,

under constant illumination and shaking at a temperature of 24 ± 1°C. At the request of the Sponsor all concentrations were corrected for a test item water content of 12.1% and an ethylene glycol content on 4.3%,

Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter Multisizer Particle Counter.

Exposure of Pseudokirchneriella subcapitata to the test item gave the following results:

Response Variable

EC50 (mg ai/l)

95% Confidence Limits (mg ai/l)

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

Lowest Observed Concentration (LOEC) (mg/ai/l)

Growth rate

>100

*

10

32

Yield

38

29 – 50

10

32

*Not possible to calculate 95% confidence limits.

Analysis of the test preparations at 0 hours showed measured test concentrations to range from 99% to 107% of nominal. Analysis of the test preparations at 72 hours showed measured test concentrations to be near nominal with the exception of the

1.0 mg ai/l test concentration which showed a measured concentration of 46% of nominal.

Given that analysis of the 1.0 and 10 mg ai/l test samples taken from the range-finding test indicated that a significant decline in measured test concentration occurred over the test period additional samples were prepared for each test concentration at 0 hours with the omission of algal cells and incubated alongside the test from which samples were taken for analysis at 72 hours. Measured concentrations in the range of 98% to 107% of nominal were obtained suggesting that the decline observed in the 1.0 mg ai/l test

sample in the definitive study was due to adsorption of the test item to the algal cells present rather than instability. As such it was considered that the algal cells were exposed to near nominal test concentrations over the test duration and therefore the results are based on nominal test concentrations only.

As the measured test concentrations in this study were shown to be near the nominal test concentrations over the test duration, it is considered that the test substance is stable in the test solutions over the test duration. It is therefore considered that the results of the marine algal, fish (freshwater and marine), Daphnia and Acartia studies, which are all based on nominal concentrations (as the test concentrations were not measured) are considered valid and applicable in the assessment of the toxicity of the test substance.

Marine study (Hudson B (2006a))

An assessment of the toxicity of the test substance to the marine alga Skeletonema costatum was performed.

Test methods were conducted in accordance with SOP 104 and ISO 10253 (1998) Water Quality - marine algal growth inhibition test.

The method assesses the growth rate of cultures in solutions of test material in enriched seawater in comparison to the growth rate of cultures in enriched seawater alone. Growth rate was measured in terms of increase in cell number or in biomass.

Test concentrations (nominal) were 100, 320, 1000, 1800, 3200 and 10000 mg/l.

The test material exhibited a 72h EC50 value of 1204.55 mg/l to the marine phytoplankton Skeletonema costatum in the aqueous phase. The No Observed Effect Concentration was determined to be 320 mg/L.

The result is based on nominal concentrations.