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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The effect of the test material on the growth of Scenedesmus subspicatus has been investigated over a 72-Hour period and gave an ErL50 (0 - 72 h) value of 0.15 mg/L loading rate WAF. The No Observed Effect Loading Rate (NOELR) at 72 hours was 0.04 mg/L loading rate WAF.

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Additional information

A Klimisch-1 -rated study was performed to assess the effect of the test material on the growth of the green alga Scenedesmus subspicatus. The method followed that described in the OECD TG 201.

Following preliminary range-finding tests, Scenedesmus subspicatus was exposed to Water Accommodated Fractions (WAFs) of the test material over a range of nominal loading rates of 0.010, 0.020, 0.040, 0.080 and 0.16 mg/L for 72 hours. Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a coulter Multisizer II Particle Counter.

Analysis of the test solutions at 0 hours showed measured test concentrations to range from less than the limit of quantitation (LOQ) which was assessed down to 0.00087 mg/L to 0.125 mg/L following a concentration dependent pattern. Analysis of the test solutions at 72 hours showed a marked decline in measured test concentrations with measured test concentrations in the range of less than the LOQ to 0.0085 mg/L. Given that the test material was considered to be stable in culture medium over the test period this decline in measured test concentrations was considered to be due to adsorption to algal cells. The pre-study recovery analyses conducted indicated that no adsorption of the test material to algal cells occurred. However, this does not preclude long term adsorption to algal cells over the test period. Adsorption was not a factor in the pre-study stability analyses conducted since no algal cells were present. Given that the toxicity cannot be attributed to a single component or a mixture of components but to the test material as a whole, and the dissolved test material was below the quantifiable limit of the analytical method, the results were based on nominal loading rates only.

Exposure of Scenedesmus subspicatus to the test material gave an EbL50 (72 h) value of 0.12 mg/L loading rate WAF; 95% confidence limits 0.11 - 0.14 mg/L loading rate WAF and an ErL50 (0 - 72 h) value of 0.15 mg/L loading rate WAF. The No Observed Effect Loading Rate (NOELR) was 0.040 mg/L loading rate WAF.