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The effect of the test material was assessed on algal growth using the unicellular green alga Pseudokirchneriella subcapitata (Selenastrum capricornutum), over an exposure period of 72 hours.

This study has been performed to the standardised guideline OECD 201 and under GLP conditions. The study has therefore been assigned a reliability score of 1 in line with the principles for assessing data quality as defined by Klimisch et al. (1997).

As the test material is a water soluble deep-coloured powder and the amount of light for photosynthesis is likely to be significantly affected by the shading effect of the coloured test solution, therefore a modified test was performed in order to separate physical effect of the coloured material from its true toxic effects.

Five test concentrations in a geometric series with a separation factor of 3.2 and one untreated control were tested in the main experiment. The test design included three replicates at each test group (light filter and treated group) and six replicates for the untreated control.

The nominal concentrations of test material used in the main experiment were: 1.0, 3.1, 9.8, 31.3 and 100 mg/L.

The test material concentrations were analytically determined at the start and at the end of the experiment. As the measured concentrations deviated not more than 20 per cent from the nominal in all case, biological results are based on the nominal concentrations.

Statistical comparisons of biomass, average specific growth rates and yield in control and in test material groups (filter and treated groups) were carried out using analysis of variance (ANOVA), Bonferroni t-Test and Dunnett’s Test (α = 0.05) by TOXSTAT software.

The corrected ErC50, EbC50 and EyC50 values of the test material were determined directly from the raw data. The non-corrected ErC50, EbC50 and EyC50 values of the test material and their confidence limits were calculated using Probit analysis by TOXSTAT software.

Under the conditions of the study, the results of this experiment showed that the majority of the observed inhibition effect was related to the light absorption by the test material. However, a greater inhibition was seen at 72 hours when the test material was in contact with the algae cells for 72 hours. This indicates that there was also a toxic effect on the growth of the alga (Pseudokirchneriella subcapitata).