Alkenes, C20-24-branched and linear

Toxicity to aquatic algae and cyanobacteria

Description of key information

A study was performed to assess the effect of the test material on the growth of the green alga Desmodesmus subspicatus.  The method followed that described in the OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" referenced as Method C.3 of Commission Directive 92/69/EEC (which constitutes Annex V of Council Directive 67/548/EEC).
The effect of the test material on the growth of Desmodesmus subspicatus has been investigated and gave EL*50 values of greater than 100 mg/l loading rate WAF.  Correspondingly the No Observed Effect Loading Rate was 100 mg/l loading rate WAF.
EL = Effective Loading Rate

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

Additional information

Introduction:

A study was performed to assess the effect of the test material on the growth of the green alga Desmodesmus subspicatus. The method followed that described in the OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" referenced as Method C.3 of Commission Directive 92/69/EEC (which constitutes Annex V of Council Directive 67/548/EEC).

Methods:

Following a preliminary range-finding test, Desmodesmus subspicatus was exposed to a Water Accommodated Fraction (WAF) of the test material, at a single nominal loading rate of 100 mg/l (six replicate flasks) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1°C.

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

A positive control conducted approximately every six months used potassium dichromate as the reference material. Desmodesmus subspicatus was exposed to an aqueous solution of the reference material at concentrations of 0.0625, 0.125, 0.25, 0.50 and 1.0 mg/l (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1°C.

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

Results.

Exposure of Desmodesmus subspicatus to the test material gave EL₅₀ [1] values of greater than 100 mg/l loading rate WAF and correspondingly the No Observed Effect Loading Rate was 100 mg/l loading rate WAF. It was considered unnecessary and unrealistic to test at loading rates in excess of 100 mg/l.

Analysis of the test preparations at 0 hours showed measured concentrations in the range 0.0515 to 0.0525 mg/l. A decline in measured concentrations was observed at 72 hours in the range less than the limit of quantitation (LOQ) of the analytical method, which was assessed as 0.0052 mg/l, to 0.0057 mg/l. This decline, in excess of that seen in the stability analyses, was considered to be due to possible adsorption of the test material to the algal cells present. Whilst no immediate adsorption was observed in the recovery analyses conducted in the presence of algal cells, this does not preclude long-term adsorption over the test period. Adsorption was not a factor in the stability analyses conducted since no algal cells were present.

Given that toxicity cannot be attributed to a single component or a mixture of components but to the test material as a whole the results were based on nominal loading rates only.

Exposure of Desmodesmus subspicatus to the reference material, potassium dichromate, gave an E_rC₅₀ (0 - 72 h) of 0.64 mg/l*, an E_yC₅₀ (0 - 72 h) of 0.36 mg/l; 95% confidence limits 0.30 - 0.43 mg/l, and an E_bC₅₀ (0 - 72 h) of 0.32 mg/l; 95% confidence limits 0.29 - 0.35 mg/l. 

The Lowest Observed Effect Concentration based on inhibition of growth rate, yield and biomass integral was 0.25 mg/l and the No Observed Effect Concentration was 0.125 mg/l. 

The effect of the test material on the growth of Desmodesmus subspicatus has been investigated and gave EL₅₀ values of greater than 100 mg/l loading rate WAF. Correspondingly the No Observed Effect Loading Rate was 100 mg/l loading rate WAF.

[1]EL = Effective Loading Rate

*It was not possible to calculate 95% confidence limits for the E_rC₅₀ value as the data generated did not fit the models available for the calculation of confidence limits.