Disodium 2,5-dichloro-4-[4-[[5-[[(dodecyloxy)carbonyl]amino]-2-sulphonatophenyl]azo]-4,5-dihydro-3-methyl-5-oxo-1H-pyrazol-1-yl]benzenesulphonate

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:

October 30th and 31st, 1990

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

not specified

Test organisms (species):

activated sludge

Details on inoculum:

- Source: the aeration Stage of Severn Trent PLC Sewage Treatment Plant, Belper, Derbyshire.
- Maintainance: 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 4.0 g/l prior to use.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Nominal and measured concentrations:

10 mg/l

Details on test conditions:

TEST SYSTEM
- No. of vessels per concentration: 3 replicates
- No. of vessels per control: 2 replicates

RANGE FINDING
- Concentrations: 1, 10, 100 and 1000 mg/l

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Results with reference substance (positive control):

EC50 (3h): 10.5 mg/l

Main test

Concentration (mg/l )	O2consumption rates mg/O2/l/min	% inhibition
Control	0.43	-
Control	0.40	-
Test item 10	0.38	8
Test item 10	0.45	<8>
Test item 10	0.42	<1>
3,5-dichlorophenol 3.2	0.47	<13>
3,5-dichlorophenol 32	0.04	90

<increase>

Variation between controls: ± 4 %

Range-finding test

Concentration (mg/l )	O2consumption rates mg/O2/l/min	% inhibition
Control	0.42	-
Control	0.36	-
Test item 1.0	0.33	15
Test item 10	0.33	15
Test item 100	0.25	36
Test item 1000	0.19	51
3,5-dichlorophenol 3.2	0.30	23
3,5-dichlorophenol 32	0.06	85

<increase>

Variation between controls: ± 8 %

Conclusions:

EC50 (3h) > 10 mg/l (nominal)

Executive summary:

Activated sludge respiration inhibition test has been performed on test item. A range-finding investigation was conducted at the nominal concentrations of 1.0, 10, 100 and 1000 mg/l. The main test was conducted at the nominal concentration of 10 mg/l; three replicates were assayed. Blank control and reference item, 3,5-dichlorophenol, have also been tested.

Only slight effects were recorded: the percentage of the respiration inhibition was 8 %. The EC50 after 3 hours of contact time has been indicate as higher than 10 mg/l.

Conclusion

EC50 (3h) > 10 mg/l (nominal)

Description of key information

EC50 (3h) > 10 mg/l

Additional information

Activated sludge respiration inhibition test was performed on test item. A range-finding investigation was conducted: 15 % of inhibition was recorded at the concentrations of 1.0 and 10 mg/l; at 100 mg/l the inhibition was ca 36 %, while at 1000 mg/l the inhibition regarded the 51 % of microorganisms population. On the basis of the preliminary investigation outcomes, the nominal concentration selected for the main test was 10 mg/l. Only slight effects were recorded: the percentage of the respiration inhibition was 8 %. The EC50 after 3 hours of contact time has been indicate as higher than 10 mg/l. However, considering also the outcomes obtained into the range-finding test, the EC50 is expected to be higher than 100 mg/l.

A second test is available; the experiment was run with aerobic activated sludge from a domestic waste-water treatment plant. In this case, the respiration rate of the sludge resulted to be inhibited up to ca 57 % at the highest concentration of 100 mg/l.