[No public or meaningful name is available]

Toxicity to aquatic algae and cyanobacteria

Description of key information

OECD Guideline 201, EU Method C.3, GLP, key study, validity 2:
72h-ErC50 = 20 mg/L (geometric mean measured concentrations);
72h-ErC10 = 11 mg/L (geometric mean measured concentrations).

Key value for chemical safety assessment

EC50 for freshwater algae:

20 mg/L

EC10 or NOEC for freshwater algae:

11 mg/L

Additional information

One key study is available to assess the effect of the test material on the growth of the green alga Desmodesmus subspicatus, according to OECD Guideline 201 and EU Method C.3 with GLP statement.

Following a preliminary range-finding test, Desmodesmus subspicatus was exposed to solutions of the test material at nominal concentrations of 1.0, 3.2, 10, 32 and 100 mg/l (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24±1°C. The test material solutions were prepared by shaking an excess (100 mg/l) of test material in culture medium (INFORS Aerotron) at approximately 300 rpm at a temperature of 30°C for 24 hours. After the shaking period any undissolved test material was removed by filtration (0.2 µm Gelman Acrocap filter, first approximate 100 ml discarded in order to precondition the filter) to produce a saturated solution of the test material with a nominal concentration of 100 mg/l. This saturated solution was then further diluted as necessary, to provide the remaining test groups.

Due to the nature of the test material testing was conducted in completely filled, stoppered test vessels in order to minimise possible losses due to volatilisation. Following the recommendations of published data (Hermanet al1990) in order to prevent inhibition of growth due to the restriction of gaseous exchange, additional sodium bicarbonate was added to the culture medium to provide a source of carbon dioxide for algal growth.

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

Analysis of the test preparations at 0 hours showed measured test concentrations to range from 82% to 116% of nominal. Analysis of the test preparations at 72 hours showed a slight decline in measured test concentrations in the range of 74% to 91% of nominal.

Due to the nature of the test material, additional test replicates were prepared at 0 hours and incubated alongside the test to provide samples for unopened vessel analysis at 72 hours.

Analysis of these preparations showed measured test concentrations to range from 78% to 107% of nominal. Given that these measured concentrations were similar to those obtained from the test vessels which had been opened it was considered that the decline seen in the 72-Hour test samples was due to possible adsorption of the test material to the algal cells present rather than losses due to volatility. Whilst the preliminary recovery analyses conducted in the presence of algal cells indicated that no immediate adsorption occurred this does not preclude long-term adsorption over the test period. Adsorption was not a factor in the preliminary stability analyses conducted as no algal cells were present.

Given this decline in measured test concentrations it was considered justifiable to base the results on the geometric mean measured test concentrations in order to give a "worst case" analysis of the data.

The ErC50 and ErC10 (0 - 72 h) based on the geometric mean measured test concentrations were 20 mg/l and 11 mg/L, respectively. The Lowest Observed Effect Concentration based on inhibition of growth rate was 32 mg/l and the No Observed Effect Concentration was 8.4 mg/l.