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Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

April to May 2019

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 (Carbon and Ammonium Oxidation))

Deviations:

yes

Remarks:

The test temperatures were slightly higher than the OECD recommended range (18 – 22 °C); this deviation was considered acceptable and without influence on test results, since all the validity criteria were met.

GLP compliance:

yes (incl. QA statement)

Test organisms (species):

activated sludge

Details on inoculum:

The study was performed using activated sludge collected from the aeration tank of BRIANZACQUE wastewater treatment plant treating domestic wastewater. 10 litres of activated sludge were collected on April 16, 2019 and transferred to Test Facility where they were immediately set under aeration and shaking in dark conditions.
The temperature of the sludge on receipt was 16.0 °C.

Test type:

static

Water media type:

freshwater

Total exposure duration:

3 h

Test temperature:

21.5-24.7

pH:

7.60-8.64

Nominal and measured concentrations:

9.5, 30.5, 97.7, 312.5 and 1000 mg test item/L

Details on test conditions:

Tightly closed plastic bottles (1500 mL capacity) were used and sludge oxygen demand was satisfied stirring the bottles with an orbital shaker at 200 rpm, as suggested by the OECD guideline No. 209 (2010) when the test item generates slightly foam.

During the incubation period, test bottles were maintained in dark conditions and test temperature was in the range 21.5 – 24.7°C with a mean value of 22.7°C and a standard deviation of 0.9°C. The recorded values were corrected according to the data logger correction factor.
During the incubation period the dissolved oxygen was greater than 60% of saturation (88%).

The pH was determined in the test item and reference item concentration bottles, in the abiotic controls and in the negative controls at the end of the test (after 3 hours of incubation), while was determined only in the test item bottles at the start of the test (before inoculum).

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

ca. 89.9 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

ca. 30.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

ca. 123.8 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of heterotrophic respiration

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

ca. 30.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of heterotrophic respiration

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

ca. 61.1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of respiration due to nitrification

Validity criteria fulfilled:

yes

Conclusions:

The toxic effect on aerobic treatment plant microorganisms of POLIOL MB-600 was tested with activated sludge after 3-hours contact.

Since a preliminary test have shown a 100% of respiration inhibition at the highest concentration (1000 mg/L of test item), a definitive test at five concentrations was performed.

In addition, during the preliminary test, two additional blank bottles with ATU were performed (N-allylthiourea), run in parallel to the blank bottles without ATU.
The difference between the respiration rate of the two series of blank bottles (without and with ATU), showed that the respiration rate due to the nitrification respiration is significant (> 5% of RT), therefore two series of test bottles in definitive test were prepared, one series without ATU and one series with ATU.

This method permitted to measure the oxygen uptake due to the total respiration (RT) and the oxygen uptake due to the heterotrophic respiration (RH). The relationship between total respiration and heterotrophic respiration allows to calculate the oxygen uptake due to nitrification respiration (RN).

Executive summary:

Title:                                              POLIOL MB-600: Toxicity to Activated sludge in a Respiration Inhibition Study

Evaluations:                                   The respiration rate of wastewater micro-organism, after three hours of incubation time.

Test concentrations:                      9.5, 30.5, 97.7, 312.5 and 1000 mg test item/L. 

Test type:                                      Definitive test without ATU and with ATU. 

Monitoring of test medium pH:      At the start only in test item bottles and at the end of the test, in all test bottle.

Test temperature:                 21.5– 24.7°C.

pH of test medium:               7.60 – 8.64 at the test start in test item bottles.

                                           7.70 – 8.51 at the test end.

pH of test medium:               7.68 – 8.63 at the test start in test item bottles.

(with ATU)                          7.72 – 8.73 at the test end.

Validity criteria:                    Achieved, according to GuidelineOECD Guideline No. 209, 2010

Results expression:               The biological results were referred to nominal concentration of test item.

Biological results:                  Based on the obtained results:

EC₅₀value for total respiration was assessed to be 89.9 mg test item/L and the NOEC value was 30.5 mg test item/L.

EC₅₀value for heterotrophic respiration was assessed to be 123.8 mg test item/L and the NOEC value was 30.5 mg test item/L 

EC₅₀value for nitrification respiration was assessed to be 61.1 mg test item/L.

 Abiotic control:                      did not show any significant oxygen consumption

 Sensitivity test:                        The EC₅₀values of 3,5-dichlorophenol for total respiration was 9.1 mg/L, in compliance with the validity range indicated by the reference guidelines (EC₅₀: 2 - 25 mg/L).

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Read across from structural analogue, justification can be found attached in section 13.2.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

ca. 61.1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of respiration due to nitrification

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

ca. 30.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of heterotrophic respiration

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

ca. 123.8 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of heterotrophic respiration

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

ca. 30.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

ca. 89.9 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Validity criteria fulfilled:

yes

Conclusions:

EC50value for total respiration was assessed to be 89.9 mg test item/L and the NOEC value was 30.5
mg test item/L.
EC50value for heterotrophic respiration was assessed to be 123.8 mg test item/L and the NOEC value
was 30.5 mg test item/L
EC50value for nitrification respiration was assessed to be 61.1 mg test item/L.

Description of key information

EC50 for microorganisms 89.9 mg/L

Key value for chemical safety assessment

EC50 for microorganisms:

89.9 mg/L

EC10 or NOEC for microorganisms:

30.5 mg/L