Benzyl 4-[(1-butyl-5-cyano-1,6-dihydro-2-hydroxy-4-methyl-6-oxopyridin-3-yl)azo]benzoate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

11 September to 12 September, 1990

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

not specified

Analytical monitoring:

not specified

Vehicle:

no

Details on test solutions:

- Preparation: the sample was maintained at 21 °C with continuous aeration and used on the day of collection. The pH was buffered to pH 7.1 with sodium hydroxide solution and the suspended solids level adjusted to 4.1 g/l prior to use.

Test organisms (species):

activated sludge of a predominantly industrial sewage

Details on inoculum:

- Inoculum: a mixed population of activated sewage sludge microorganisms
- Source: the aeration stage of Severn Trent PLC Sewage Treatment Plant, Belper, Derbyshire
- Method of preparation: direct dispersion in water

Test type:

not specified

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Post exposure observation period:

No post exposure observation period

Test temperature:

Room temperature

pH:

7.1

Nominal and measured concentrations:

Measured concentrations are not specified. Nominal concentrations are used for all evaluations.

Details on test conditions:

TEST SYSTEM
- No. of vessels per concentration: 3 replicates
- No. of vessels per control: 2 replicates
- Adjustment of pH: buffered to pH 7.1 with sodium hydroxide solution

TEST CONCENTRATIONS
- Concentrations used in range finding study : 10, 100 and 1000 mg/l
- Results used to determine the conditions for the definitive study: percentage inhibition
- Definitive test concentrations: 1000 mg/l (3 replicates; limit test)

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Details on results:

- Percentage inhibition of test item: 0-7 % (3 replicates)

Results with reference substance (positive control):

- Percentage inhibition of reference item: 12-79 % (2 replicates)
- 3 hour EC50 = 12 mg/l

Table 1: Results from the range finding study.

Substance	Concentration (mg/l)	O2 consumption rates (mg/O2/min) 3 hour contact time	% inhibition
Control	0.0 0.0	0.36 0.41	- -
Test item	10 100 1000	0.42 0.34 0.33	<9> 12 14
Reference item	3.2 32	0.33 0.06	14 84

<increase>

Variation between controls: ± 6 %

Table 2: Results from the definitive study.

Substance	Concentration (mg/l)	O2 consumption rates (mg/O2/min) 3 hour contact time	% inhibition
Control	0.0 0.0	0.42 0.42	- -
Test item	1000 1000 1000	0.42 0.42 0.45	0 0 <7>
Reference item	3.2 32	0.37 0.09	12 79

<increase>

Variation between controls: zero

Conclusions:

The 3 hour EC50 of the test item to microorganisms is greater than 1000 mg/l (nominal).

Executive summary:

The potential for the test item to inhibit activated sludge respiration was evaluated in an experimental study according to a method comparable to the OECD guideline 209. In a range finding study, a mixed population of activated sewage sludge microorganisms exposed to test item concentrations of 10, 100 and 1000 mg/l for 3 hours inhibited oxygen consumption by -9 % (increase), 12 % and 14 %, respectively, compared to two replicates of a negative control. A reference substance (3,5-dichlorophenol: 3.2 and 32 mg/l) were tested in parallel which inhibited oxygen consumption by 14 % and 84 % at 3.2 and 32 mg/l, respectively. Based on these findings, a limit test was performed in the definitive study using the highest concentration.

In the definitive study, three replicates of 1000 mg/l were not found to inhibit oxygen consumption compared to two replicates of the negative control: oxygen consumption was inhibited by the test item by 0 %, 0 % and -7 % (increase). Based on this finding, the 3 hour EC₅₀ of the test item was found to be greater than 1000 mg/l.

Oxygen consumption of the reference substance was inhibited by 12 % and 79 % at concentrations of 3.2 and 32 mg/l, respectively, therefore the 3 hour EC₅₀ of the reference substance was found to be 12 mg/l. Analytical determinations of test item concentration were not performed during the study, therefore, all findings are based on the nominal test item concentrations.

Description of key information

EC₅₀ (3 h) > 1000 mg/l (nominal)

Additional information

Toxicity of the substance to microorganisms was examined in a 3 hour exposure to the test item in an activated sludge respiration inhibition limit test. 1000 mg/l test item was not found to inhibit oxygen consumption, therefore, the concentration which reduced oxygen consumption by 50 % (EC₅₀) after 3 hours of exposure is greater than 1000 mg/l, reported as nominal concentration due to poor water solubility.