2,2'-[1,2-ethanediylbis(oxy)]bis(ethanethiol)

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:

01-02-2017 to 08-10-2017

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 (Carbon and Ammonium Oxidation))

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

The definitive test was conducted using a range of concentrations deduced from the preliminary range-finding test: activated sewage sludge micro-organisms were exposed to a series of nominal test concentrations of 9.5, 30.5, 97.7, 312.5 and 1000.0 mg/L. In order to obtain both a NOEC and EC50, five treatment concentrations in a geometric series with 2 replicates were prepared. The test item was dispersed directly in ultra-pure water.

The reference item, 3,5-dichlorophenol, was included at concentrations of 3.2, 10 and 32 mg/L in order to confirm again the suitability of the inoculum (test solutions were prepared with a single replicate from the same stock solution as the range-finding test).

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Two inoculum were used for this study: the first one (for the preliminary range-finding test) was obtained on 02 January 2017 and the second one (for the definitive test) on 24 July 2017. Both were sampled from the activated sludge of the biological wastewater treatment plant from Mourenx (France, 64) which handles predominantly domestic sewage.

On arrival at the laboratory, the activated sludge was centrifuged (1000g for 10 minutes) and the solid sewage inoculum pellet was re-suspended in 10L deionised water. 500 mL synthetic sewage feed was then added. Sewage sludge was maintained under aerated conditions for a maximum of 5 days and fed daily with synthetic sewage feed.

In order to obtain the required sludge suspended solids concentration of 3 g/L in the stock solution to be used in the experiments, the solid content of the 10-L sludge solution was determined by removing a sub-sample of homogenised sludge and drying in an oven at approximately 105°C. The suspended solids concentration was subsequently adjusted with the source water until the recommended guideline value of 3 g/L ± 10% is achieved.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

The temperature was monitored throughout the test period.

For the range finding test, the recorded temperatures were as follows:!
- Room 1: mean measured temperature: 20.8°C, min.: 20.2°C, max.: 21.1°C.
- Room 2: mean measured temperature: 21.0°C, min.: 20.8°C, max.: 21.3°C.

The ambient temperature during the definitive test did remain constant at 20°C within ± 2°C: mean measured temperature: 20.6°C, min.: 20.5°C, max.: 20.6°C.

pH:

Measured pH were all at 7.5, no adjustment was necessary.

Nominal and measured concentrations:

Nominale concentrations: 9,5 - 30,5 - 97,7 - 312,5 - 1000 mg/L

Details on test conditions:

All solutions were incubated at 20 +/- 2°C in darkness for 3 hours in a temperature controlled room. Solutions were mixed by stirring and aerated with clean, oil-free compressed air via narrow bore glass tubes at a rate of 0.5 to 1.0 liter per minute during 3 hours. At the end of the incubation period, a well-mixed sample of each solution (following their order of preparation) were poured into a BOD bottle in which dissolved oxygen concentrations were measured at 1 min intervals for up to a maximum period of 10 min or until the oxygen concentration felt below 1 mg/L.

Reference substance (positive control):

yes

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

772.1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

67.4 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

Total respiration was inhibited at each tested concentrations as described below in the table 1:

Results with reference substance (positive control):

The 3h-EC50 for the reference item (21.5 mg/L) passed the validity criterion of the guideline set between 2 and 25 mg/L for total respiration

Reported statistics and error estimates:

EC10, EC50, LOEC and NOEC values under the conditions of this test were calculated for the test item: see table 2.

Table 1:

Test item nominal concentration (mg/L)	Inhibition of total respiration (%)
9.5	7.3
30.5	10.7
97.7	16.0
312.5	29.7
1000.0	59.0

Table 2:

		95% confidence level
		Lower limit	Upper limit
NOEC	30.5 mg/L	NA	NA
LOEC	97.7 mg/L	NA	NA
EC10	67.4 mg/L	30.1	150.9
EC50	772.1 mg/L	275.7	2016.3

Validity criteria fulfilled:

yes

Conclusions:

This study was designed to determine the inhibition of respiration rates of an activated sludge by the test item following the procedure described in the corresponding OECD guideline 209.

EC10, EC50, LOEC and NOEC values under the conditions of this test were calculated to be as follows for the test item:

95% confidence level
Lower limit Upper limit
NOEC 30.5 mg/L NA NA
LOEC 97.7 mg/L NA NA
EC10 67.4 mg/L 30.1 150.9
EC50 772.1 mg/L 275.7 2016.3
NA: Not Applicable

Executive summary:

This study was designed to determine the effects of the test item on sewage micro-organisms by measuring the respiration rate in 3 hours test according to the OECD Guideline 209 (July 2010).

The inhibition of oxygen uptake by ammonium oxidation (i.e. nitrification) was not determined, so that only total respiration inhibition was assessed in this study.

The definitive test was conducted at the following nominal concentrations: 9.5, 30.5, 97.7, 312.5 and 1000.0 mg/L.

A reference item (3, 5-dichlorophenol) was tested as a reference inhibitory substance at the following nominal concentrations: 3.2, 10.0 and 32.0 mg/L.

The prepared vessels were aerated for 3h, after which dissolved oxygen concentrations were measured at 1 min intervals for up to a maximum period of 10 min. The respiration rate for each vessel was calculated from the measured values of recorded oxygen concentrations versus time andexpressed as mg O₂/L/h for the linear part of the graphs (then converted in mg O₂/g of activated sludge dry weight of suspended solids/h).

 

The definitive test met the validity criteria of the guideline detailed as follows:

- The coefficient of variation of oxygen uptake rate in the controls should be no more than 30% at the end of the definitive test: it was determined to be 7.3%

- The 3h-EC50 for the reference item (21.5 mg/L) passed the validity criterion of the guideline set between 2 and 25 mg/L for total respiration

- The blank controls oxygen uptake was not less than 20 mg oxygen/g of activated sludge (dry weight of suspended solids) in an hour: 25.45 mg O₂/g of activated sludge (dry weight of suspended solids)/h

  

EC10, EC50, LOEC and NOEC values under the conditions of this test were calculated to be as follows for the test item:

 

		95% confidence level
		Lower limit	Upper limit
NOEC	30.5 mg/L	NA	NA
LOEC	97.7 mg/L	NA	NA
EC10	67.4 mg/L	30.1	150.9
EC50	772.1 mg/L	275.7	2016.3

NA: Not Applicable

 

 

 

Description of key information

This study was designed to determine the effects of the test item on sewage micro-organisms by measuring the respiration rate in 3 hours test according to the OECD Guideline 209 (July 2010).

The inhibition of oxygen uptake by ammonium oxidation (i.e. nitrification) was not determined, so that only total respiration inhibition was assessed in this study.

The definitive test was conducted at the following nominal concentrations: 9.5, 30.5, 97.7, 312.5 and 1000.0 mg/L.

A reference item (3, 5-dichlorophenol) was tested as a reference inhibitory substance at the following nominal concentrations: 3.2, 10.0 and 32.0 mg/L.

The prepared vessels were aerated for 3h, after which dissolved oxygen concentrations were measured at 1 min intervals for up to a maximum period of 10 min. The respiration rate for each vessel was calculated from the measured values of recorded oxygen concentrations versus time andexpressed as mg O₂/L/h for the linear part of the graphs (then converted in mg O₂/g of activated sludge dry weight of suspended solids/h).

 

The definitive test met the validity criteria of the guideline detailed as follows:

- The coefficient of variation of oxygen uptake rate in the controls should be no more than 30% at the end of the definitive test: it was determined to be 7.3%

- The 3h-EC50 for the reference item (21.5 mg/L) passed the validity criterion of the guideline set between 2 and 25 mg/L for total respiration

- The blank controls oxygen uptake was not less than 20 mg oxygen/g of activated sludge (dry weight of suspended solids) in an hour: 25.45 mg O₂/g of activated sludge (dry weight of suspended solids)/h

  

EC10, EC50, LOEC and NOEC values under the conditions of this test were calculated to be as follows for the test item:

 

		95% confidence level
		Lower limit	Upper limit
NOEC	30.5 mg/L	NA	NA
LOEC	97.7 mg/L	NA	NA
EC10	67.4 mg/L	30.1	150.9
EC50	772.1 mg/L	275.7	2016.3

NA: Not Applicable

Key value for chemical safety assessment

EC50 for microorganisms:

772.1 mg/L