Carbonohydrazide

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 gave the following results (geometric mean):
Growth Rate: 
EC50: 1.5 mg/l
Yield: 
EC50: 0.46 mg/l
NOEC: (growth rate and yield): 0.074 mg/l
LOEC:  (growth rate and yield): 0.28 mg/l

Key value for chemical safety assessment

EC50 for freshwater algae:

1.5 mg/L

EC10 or NOEC for freshwater algae:

0.074 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 was designed to be compatible with 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 440/2008.

Methods.

Following a preliminary range-finding test, Pseudokirchneriella subcapitata was exposed to an aqueous solution of the test item at concentrations of 0.10, 0.32, 1.0, 3.2 and 10 mg/l (three replicate flasks per concentration) 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.

Results

Exposure of Pseudokirchneriella subcapitata to the test item gave the following results:

Response Variable	EC50(mg/l)	95% Confidence limits (mg/l)	NOEC (mg/l)	LOEC (mg/l)
Growth rate	1.5	1.1 - 1.9	0.10	0.32
Yield	0.50	0.44 - 0.57	0.10	0.32

 

Analysis of the test preparations at 0 hours showed that measured test concentrations to range from 94% to 111% of nominal. A decline in measured test concentrations was observed at 72 hours in the range of 58% to 109% of nominal.

Given that analysis of the range finding and stability test preparations showed evidence of possible instability and/or adsoprtion to the algal cells present additional test samples were prepared at the start of the test with the omission of the algal cells.

Analysis of these additional samples at 0 hours showed measured test concentrations in the range of 95% to 112% of nominal were obtained. Following incubation under test conditions for a period of 72 hours analysis of these samples showed a decline in measured test concentrations in the range of 63% to 91% of nominal. As such it was considered that the decline observed was due to instability rather than adsorption of the test item to the algal cells 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.

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)	NOEC (mg/l)	LOEC (mg/l)
Growth rate	1.5	1.1 – 1.9	0.074	0.28
Yield	0.46	0.40 – 0.53	0.074	0.28