Xanthylium, 3,6-bis(ethylamino)-9-[2-(methoxycarbonyl)phenyl]-2,7-dimethyl-, molybdatetungstatephosphate

Toxicity to aquatic algae and cyanobacteria

Description of key information

The effect of the test item on the growth of Pseudokirchneriella subcapitata has been investigated over a 72-Hour period and based on the geometric mean measured test concentrations gave the following results:

Growth Rate:

EC50: 0.12 mg/L

NOEC: 0.026 mg/L

LOEC: 0.084 mg/L

Yield:

EC50: 0.037 mg/L

NOEC: 0.010 mg/L

LOEC: 0.026 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:

0.12 mg/L

EC10 or NOEC for freshwater algae:

0.026 mg/L

Additional information

Introduction:

A study was performed to assess the effect of the test item on the growth of the green alga Pseudokirchneriella subcapitata. The method followed that described in the OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" referenced as Method C.3 of Commission Regulation (EC) No 761/2009.

Methods:

Information provided indicated the test item was practically insoluble in water. Preliminary solubility work conducted indicated that it was not possible to obtain a testable solution of the test item using traditional methods of preparation e.g. ultrasonication and high shear mixing.

A preliminary media preparation trial indicated that a dissolved test item concentration of approximately 0.78 mg/L was obtained from a saturated solution method of preparation indicating this to be the limit of water solubility of this item under test conditions.

Following a preliminary range-finding test, Pseudokirchneriella subcapitata was exposed to solutions of the test item at nominal concentrations of 1.0, 3.2, 10, 32 and 100% v/v saturated solution (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1°C. The test item solutions were prepared by stirring an excess (50 mg/L) of test item in culture medium using a propeller stirrer at approximately 1500 rpm for 24 hours. After the stirring period any undissolved test item was removed by filtration (0.2 µm Sartorius Sartopore filter, first approximate 1 liter discarded in order to pre-condition the filter) to produce a 100% v/v saturated solution of the test item. 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:

Analysis of the test preparations at 0 hours showed measured test concentrations to range from 0.013 to 1.21 mg/L. A decline in measured test concentration was observed at 72 hours to between 0.0082 and 0.86 mg/L (50% to 71% of the 0-Hour measured test concentrations). This decline in measured concentrations was in line with that observed in the range-finding test and was considered to be due to possible adsorption of the test item to the algal cells.

 

Analysis of test preparations that contained no algal cells at 72 hours showed a similar decline in measured concentration occurred in the range of 0.0089 to 0.95 mg/L (60% to 79% of the 0-Hour measured test concentrations) suggesting that the decline observed was due to instability rather than adsorption.

It was therefore considered appropriate to calculate the results based on the geometric mean measured test concentration only in order to give a “worst case” analysis of the data.

Exposure of Pseudokirchneriella subcapitata to the test item gave the following results based on the geometric mean measured test concentrations:

Response Variable	EC50(mg/L)	95% Confidence Limits (mg/L)			No Observed Effect Concentration (NOEC) (mg/L)	Lowest Observed Effect Concentration (LOEC) (mg/L)
Growth Rate	0.12	0.099	-	0.16	0.026	0.084
Yield	0.037	0.031	-	0.043	0.010	0.026