Z-85

Toxicity to aquatic algae and cyanobacteria

Description of key information

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.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC10 or NOEC for freshwater algae:

100 mg/L

Additional information

A key study to assess the effect of the test material on the growth of the green alga Desmodesmus subspicatus was performed in accordance with OECD Guideline No 201 and EC Method C.3. 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, 0.5, and 1.0 mg/L (three replicate flasks per concentration) for 72 hours.

Exposure of Desmodesmus subspicatus to the test material gave EL50 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.  Analysis of samples taken at 0 hours showed results of less than the limit of quantitation (LOQ) of the analytical method which was assessed to be 0.0051 mg/l. Given that the 0-hour samples were less than the LOQ, analysis of samples at 72 hours was not conducted as it would provide no additional information on exposure concentrations. Therefore given that 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 Desmodesmus subspicatus to the reference material, potassium dichromate, gave an ErC50 (0-72h) of 0.57 mg/L; 95% confidence limits 0.48 to 0.66 mg/L, an EyC50 (0-72h) of 0.32 mg/L; 95% confidence limits 0.29 to 0.35 mg/L, and an EbC50 (0-72) of 0.31 mg/L; 95% confidence limits 0.28 to 0.35 mg/L. The Lowest Observed Effect Concentration based on inhibition of growth rate, yield and biomass integral were 0.50, 0.125, and 0.125 mg/l respectively and the No Observed Effect Concentrations were 0.25, 0.0625, 0.0625 mg/l respectively.