tetrakis(2,6-dimethylphenyl)-m-phenylene biphosphate

Toxicity to aquatic algae and cyanobacteria

Description of key information

The effect of the test material on the growth of Scenedsmus subspicatus has been investigated and gave EC50 values of greater than 0.80 mg/l. Correspondingly the No Observed Effect Concentration was 0.80 mg/l.
Based on the time-weighted mean measured test concentartions the EC50 values were estimated to be greater than 0.031 mg/l. Correspondingly the No Observed effect Concentration was 0.031 mg/l.

Key value for chemical safety assessment

EC50 for freshwater algae:

0.8 mg/L

EC10 or NOEC for freshwater algae:

0.8 mg/L

Additional information

Methods:

A study was performed to assess the effect of the test material on the growth of the green algascenedesmus subspicatus. The method followed that described in the OECD Guidelines for Testing of Chemicals (1984) No 201, "Alga, Growth Inhibition Test" referenced as Method C.3 of Commission Directive 92/69/EEC (which constitutes Annex V of Council Directive 67/548/EEC).

Procedure:

Following a preliminaryrange-finding study,Scenedesmus subspicatuswas exposed to an aqueous dispersion of the test material at a concentration of 0.80 mg/l (six replicate flasks) for 72 hours, under constant illumination and shaking at 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 Multisixer Particle Counter.

Results:

Exposure of Scenedesmus subspicatus to the test material gave EC₅₀values of greater than 0.80 mg/l and correspondingly the No Observed Effect Concentration was 0.80 mg/l.

The test concentration of 0.80 mg/l was the highest attainable test concentration that could be prepared due to the limited solubility of the test material in water and auxiliary solvent and having due regard to the amount of auxiliary solvent permitted in the test under the OECD Guidelines.

During preliminary solubility and range-finding work it was difficult to determine whether all of the test material had dissolved in the test medium (by visual inspection) or whether a micro-dispersion may have formed. Pre-study samples approximately equivalent to the test concentration to be used in the definitive study were analysed directly and after filtration through 0.2 µm filters. The results showed a loss of test material from the filtered samples thereby indicating that at a test concentration of 0.80 mg/l the tets material found a micro dispersion. Therefore analysis was performed on samples of filtered and unfiltered test media during the study.

Analysis of the test solutions at 0 hours showed measured values of 104% and 87% of nominal for the unfiltered samples and 3% to 4% of nominal for the filtered samples (replicates R1 - R3 and R4 - R6 respectively).

Analysis of the test solutions at 72 hours showed measured values of 65% and 87% of nominal for the unfiltered samples and 4% and 6% of nominal for the filtered samples (replicates R1 - R3 and R4 - R6 respectively).

The measured concentrations of the unfiltered samples indicate the amount of test material which is both dispersed and dissolved in the test system. The filtered samples indicate the amount of test material in solution and thus bioavailable to the algae. It was therefore considered justifiable to base the results on the time-weighted mean measured test concentration of the filtered test material in order to give a "worst case" analysis of the data. The EC50 values based on the time-weighted mean measured test concentrations were greater than 0.031 mg/l and correspondingly the No Observed Effect Concentration was 0.031 mg/l.