1-[2-(2-chloroethoxy)phenylsulfonyl]-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea;triasulfuron (ISO)

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:

25 Apr 1989 to 27 Apr 1989

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

Version / remarks:

1984

Deviations:

yes

Remarks:

See deviations from guideline in ‘Any other information on results incl. tables’

GLP compliance:

yes (incl. QA statement)

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
Test item amounts of 0.43, 0.66, 2.09, 6.47, and 20.13 mg were weighed and added to the test medium. The volume was adjusted to 200 mL with water and aerated for 3 hours. The sludge concentration in the test bottles was 1.6 g/L.

Test organisms (species):

activated sludge

Details on inoculum:

- Location of sewage treatment plant where inoculum was collected: CH - 4106 Therwil
- Date of collection: 24 Apr 1989
- Preparation of inoculum for exposure: The preparation was carried out according to the method described in the guideline. The sludge was separated from the aqueous layer by settling instead of centrifugation.
- Pretreatment: A nutrient solution was added to the sludge.

* Nutrient solution (per liter dechlorinated drinking water):
- 16 g Peptone
- 11 g Meat extract
- 3.0 g Urea
- 0.7 g NaCl
- 0.4 g CaCl2 · 2H2O
- 0.2 g MgSO4 · 7H2O
- 2.8 g K2HPO4

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

20 ± 2°C

Nominal and measured concentrations:

- Nominal concentrations: 0 (blank control) 2.1, 3.3, 10.4, 32.4 and 100.7 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 250 mL BOD flasks with gas inlet
- Fill volume: 200 mL
- Aeration: Yes, during the 3-hour exposure period
- No. of vessels per concentration: 1
- No. of vessels per blank (negative) control: 2
- Number of vessels per positive control: 3
- Sludge concentration: 1.6 g/L

EFFECT PARAMETERS MEASURED
Oxygen consumption was measured per hour in mg/litre with an oxygen electrode, a microprocessor and plotted on a recorder. The inhibitions were calculated on the basis of the measured time depend oxygen consumption of a blank and test solution.

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol; at nominal concentrations of 3.2, 10 and 32 mg/L

Key result

Duration:

3 h

Dose descriptor:

IC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

An overview of the results is provided in Table 1 in ‘Any other information on results incl. tables’.
The inhibitory effect of the test item at nominal concentrations of 2.1, 3.3, 10.4, 32.4 and 100.7 mg/L was -1, 19, 26, 10 and 26 %, respectively, after the incubation period of 3 hours.

Results with reference substance (positive control):

An overview of the results is provided in Table 1 in ‘Any other information on results incl. tables’. The inhibitory effect of the reference substance at nominal concentrations of 3.2, 10.0 and 32.0 mg/L was 17, 39 and 81 %, respectively, after the incubation period of 3 hours. The 3-hour IC50 of the reference item 3,5-dichlorophenol (positive control) was 12 mg/L (no 95% confidence limits were calculated).

Table 1. Influence of the test item and 3,5-dichlorophenol on the oxygen consumption of activated sludge

 

Substance	Conc.	Consumption rate	Inhibition
	mg/L	mg/L/h	%
Blank 1	0.0	68.64	-3
Reference	32.0	12.96	81
Reference	10.0	40.67	39
Reference	3.2	55.31	17
Blank 2	0.0	64.86	3
Test item	100.7	49.26	26
Test item	32.4	60.40	10
Test item	10.4	49.57	26
Test item	3.3	54.19	19
Test item	2.1	67.20	-1

Deviations

Instead of a centrifuged sludge a settled sludge was used. Due to the poor solubility of the test item at test conditions, direct weighted amounts were added to the test medium instead of a stock solution.

Validity criteria fulfilled:

yes

Conclusions:

In an activated sludge respiratory inhibition test performed in accordance with OECD TG 209, the 3-hour IC50 value was determined to be > 100 mg/L for inhibition of the total respiration of the microorganisms in activated sludge.

Executive summary:

An activated sludge respiratory inhibition test with the test item was performed according to OECD TG 209 and GLP principles. Activated sludge collected from a sewage treatment plant was placed in test bottles to which the test item was added. The final nominal concentrations of the test item were 0 (blank control), 2.1, 3.3, 10.4, 32.4 and 100.7 mg/L. The temperature during the incubation period was kept at 20 ± 2°C. Due to the low water solubility of the test item, the test item was weighed directly into the test flasks. The aqueous dispersions were prepared in dechlorinated drinking water with added nutrients. 3,5-Dichlorophenole was used as positive control and tested at concentrations of 3.2, 10 and 32 mg/L under the same experimental conditions. During the 3 hours incubation period, the test vessels were continuously aerated. The dissolved oxygen concentration was continuously recorded and the respiration rates calculated. The inhibitory effect of the test item was graphically determined.

After 3 hours of incubation, 17%, 39% and 81% of inhibition on oxygen consumption were observed in the positive control groups at 3.2, 10 and 32 mg 3,5 -Dichlorophenole/L, respectively. The inhibitory effect of the test item at nominal concentrations of 2.1, 3.3, 10.4, 32.4 and 100.7 mg/L was -1, 19, 26, 10 and 26 %, respectively. Therefore, the IC50 value of the test item was determined to be > 100 mg/L for inhibition of the total respiration of the microorganisms in the activated sludge.

Description of key information

3-h IC50 > 100 mg/L, activated sludge, inhibition of total respiration, OECD TG 209, Bader, 1989

Key value for chemical safety assessment

EC50 for microorganisms:

100 mg/L

Additional information

One study is available for this endpoint, which was selected as the key study. In this study performed according to OECD TG 209 and in compliance with GLP, the activated sludge collected from a sewage treatment plant was exposed to the test item at concentrations of 0 (blank control), 2.1, 3.3, 10.4, 32.4 and 100.7 mg/L for 3 hours at 20 ± 2 °C. In addition, 3,5-Dichlorophenole was used as positive control and tested at 3.2, 10 and 32 mg/L concentrations under the same experimental conditions. After 3 hours of incubation, oxygen consumption was inhibited by 17%, 39% and 81% at the 3.2, 10 and 32 mg/L 3,5-Dichlorophenole treated groups, respectively, confirming the suitability of the activated sludge used. For the test item treated groups, -1, 19, 26, 10 and 26% of inhibition was observed at 2.1, 3.3, 10.4, 32.4 and 100.7 mg/L, respectively. Based on the findings, the 3-h IC50 value of the test item was determined to be > 100 mg/L for inhibition of the total respiration of the microorganisms in the activated sludge.