Indeno[4,5-d]-1,3-dioxin, 4,4a,5,6,7,8,9,9b-octahydro-7,7,8,9,9-pentamethyl-

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 Scenedesmus subspicatus according to OECD TG 201. The ECr50 was > 14.4 mg/l. An ECr10 or 1.9 mg/l was derived and a NOEC of 0.78 mg/l, based on measured concentrations. For the risk assessment the EC10 will be used. 

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

1.9 mg/L

Additional information

A 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 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).

Following a preliminary range-finding test, Scenedesmus subspicatus was exposed to solutions of the test material at nominal concentrations of 1.25, 2.5, 5.0, 10 and 20 mg/L (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1 °C. The test material solutions were prepared by stirring an excess (100 mg/L) of test material in culture medium using a propeller stirrer at approximately 2000 rpm at a temperature of 25 °C for 24 hours. After the stirring period any undissolved test material present was removed by filtration (0.2 µm Gelman Suporcap filter, first approximate 1 litre discarded in order to pre-condition the filter) to produce a saturated solution with a nominal concentration of 20 mg/L. This saturated solution was then further diluted, as necessary, to provide the remaining test groups.

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 Scenedesmus subspicatus to the test material gave an E_rC₅₀(0 - 72 h) value of > 14.4 mg/l. The EC10 for growth rate was 1.9 mg/L. Both values are based on geometric mean concentrations.

Analysis of the test preparations at 0 hours showed the measured concentrations to be near nominal. After 72-Hours there was a marked decline in measured concentrations to 37 % to 53 % of nominal values. Stability analyses indicated that the test material was stable in aqueous medium over the test period and hence the decline in measured concentrations was considered to be due to adsorption to algal cells. Adsorption was not a factor in the stability analyses conducted as no algal cells were present. Given this decline in measured test concentrations it was considered justifiable to base the results on the geometric mean measured test concentrations in order to give a "worst case" analysis of the data.