OO-tert-butyl monoperoxymaleate

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:

28 September - 5 October 2017

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:

July 22, 2010

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: M-161001 (according to CoA from 5 September 2017)
- Expiration date of the lot/batch: 2017-10-07

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Keep only in the original container. Protect from heat and direct sunlight. Store at max. +30°C
- Stability under test conditions: Not stable

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

A weight of 103.3 – 103.8 mg of the test item was added directly into the test vessels 7 - 11 with a test volume of 500 mL to obtain a final concentration of 99.9 – 100.4 mg/L. The pH of the test solution was measured before addition of inoculum.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Activated sludge from the municipal wastewater treatment plant Staufener Bucht was used as test system. The treatment plant has a capacity of 140,000 inhabitant equivalents and clarifies predominantly domestic wastewater. Sampling date of activated sludge was 4 October 2017. The activated sludge was kept aerated until use at test temperature. The activated sludge was washed twice by settling the sludge, decanting the supernatant and re-suspending the sludge in chlorine-free tap water. Dry solid of the activated sludge was determined as 4.5 g/L by weight measurements before and after drying at 105°C (mean of triplicate measurements). Before using, the activated sludge was diluted to 3 g/L dry solids with chlorine-free tap water, in order to obtain a final concentration of 1.5 g/L dry solids in the test.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

The temperature range within the test duration was between 20.4 and 20.7°C.

pH:

The pH in the test vessels was 6.9 and was adjusted to 7.2–7.3.
The pH in the blank vessels was 7.3.

Nominal and measured concentrations:

Nominal test item concentration: 100 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 1000 mL glass beakers (Schott, Mainz, Germany))/250-300 mL BOD bottles
- Type (delete if not applicable): open
- Aeration: All vessels were stirred and aerated throughout the contact time with room air to assure an oxygen saturation of 60-70% using a membrane pump. Before starting the test the oxygen saturation rate was measured.
- No. of vessels per concentration (replicates): 6
- No. of vessels per control (replicates): 3
- Sludge concentration (weight of dry solids per volume): A final concentration of 1.5 g d.w./L was used in the test.
- Nutrients provided for bacteria: Synthetic sewage feed
- Nitrification inhibitor used (delete if not applicable): none

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: chlorine-free tap water

OTHER TEST CONDITIONS
- Adjustment of pH: yes

EFFECT PARAMETERS MEASURED (with observation intervals if applicable):
After 3 h the aeration of the first vessel was shut off and the respiration rate was measured in a BOD-bottle with an oxygen electrode while mixing with a magnetic stirrer.
This determination was repeated for each vessel at 15-min intervals, ensuring that the contact time in each vessel was 3 h.

Reference substance (positive control):

yes

Remarks:

3-5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Basis for effect:

inhibition of total respiration

Duration:

3 h

Dose descriptor:

LOEC

Effect conc.:

> 100 mg/L

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Basis for effect:

inhibition of total respiration

Results with reference substance (positive control):

- Results with reference substance valid? Yes
- Relevant effect levels: The 3-hour EC50 of 3,5-dichlorphenol was calculated as 9.24 mg/L and was therefore within the acceptable range of 2 to 25 mg/L.

Reported statistics and error estimates:

The EC50 value is calculated with the ToxRat software by probit analysis using linear maximum likelihood regression.

Table 1: Respiration rate of activated sludge after application of the test item

No.	Vessel	O2 concentration [mg/L]		Consumption rate [mg/(l*h)]	Consumption rate [mg/(gsludge*h)]	inhibition [%]
		first measurement	last measurement
1	Blank 1	7.04	5.19	44.4	29.6
2	Blank 2	7.43	5.64	43	28.6
3	Blank 3	7.86	6.85	24.2	16.2
17	Blank 4	7.39	5.89	36	24
18	Blank 5	7.43	5.93	36	24
19	Blank 6	8.17	6.63	37	24.6
7	test item 1 (100 mg/L)	7.23	5.46	42.5	28.3	-16
8	test item 2 (100 mg/L)	7.42	6.09	31.9	21.3	13
9	test item 3 (100 mg/L)	8.25	7.09	27.8	18.6	24
10	test item 4 (100 mg/L)	6.22	4.22	48	32	-31
11	test item 5 (100 mg/L)	6.39	4.77	38.9	25.9	-6
	coefficient of variation of blanks:		0.18
	mean consumption rate blanks:		24.5
	mean consumption rate test vessels:		25.2

Validity criteria fulfilled:

yes

Conclusions:

An OECD 209 Activated sludge inhibition test (2010) was performed with OO-tert-butyl monoperoxymaleate at a limit concentration of 100 mg/L after a contact time of 3 hours.
An EC50 > 100 mg/L, a LOEC < 100 mg/L and a NOEC ≥ 100 mg/L were determined.

Executive summary:

To investigate potential harmful effects of OO-tert-butyl monoperoxymaleate to microorganisms, an activated sludge respiration inhibition test was performed according to OECD 209 and under GLP.

The study was conducted to assess the inhibitory effect of the test item at a limit concentration of 100 mg/L to microorganisms of activated sludge by measuring the respiration rate after adding a standard amount of synthetic sewage feed.

The results for the inhibition of the total respiration of activated sludge after the exposure period of 3 hours were:

EC50 > 100 mg/L

LOEC > 100.0 mg/L

NOEC >= 100.0 mg/L

Consequently, OO-tert-butyl monoperoxymaleate is not considered to elicit any adverse effects against STP organisms that would identify a relevant hazard.

The test met all guideline validity criteria. 

The coefficient of variation (CV) of the blank respiration rates was less than 30% (presently 18%).

The blank controls mean oxygen uptake rate was higher than 20 mg oxygen per one gram of activated sludge per hour (presently 24.5 mg/g*h).

The 3-hour EC50 of the reference item was within the acceptable range of 2 to 25 mg/L (presently 9.24 mg/L).

Description of key information

An OECD 209 activated sludge respiration inhibition test (2010) was performed with OO-tert-butyl monoperoxymaleate. The study was conducted to assess the inhibitory effect of the test item at a limit concentration of 100 mg/L to microorganisms of activated sludge by measuring the respiration rate after adding a standard amount of synthetic sewage feed. An EC50 > 100 mg/L, a LOEC < 100 mg/L and a NOEC ≥ 100 mg/L were determined.

This shows that OO-tert-butyl monoperoxymaleate had no toxic effect on the total respiration rate of activated sludge microorganism at the concentration of 100 mg/L after the exposure period of 3 hours.

Key value for chemical safety assessment

EC50 for microorganisms:

100 mg/L

EC10 or NOEC for microorganisms:

100 mg/L

Additional information

In an activated sludge respiration inhibition study a NOEC ≥ 100 mg/L was determined. Therefore, OO-tert-butyl monoperoxymaleate is not considered to elicit any adverse effects against STP organisms that would identify a relevant hazard and may justify PNEC derivation for regulatory purposes.