2-ethylhexyl mercaptoacetate

Toxicity to microorganisms

Administrative data

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

other information

Study period:

November 26, 2008 to February 05, 2009

Reliability:

1 (reliable without restriction)

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2009

Report date:

2009

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Principles of method if other than guideline:

The test item 2-Ethylhexyl Thioglycolate is a volatile substance and therefore the test conditions according to the OECD 209 test guideline were not applicable. A modified test design was used to fulfil first the requirements of the OECD 209 and second the volatile character of the test item. The
activated sludge microorganisms were exposed to the test item for three hours in a closed system with a headspace of air and intensively mixing.
This test method of application and the test system are recommended by the test guidelines for volatile test items.

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

2-ethylhexyl mercaptoacetate

EC Number:

231-626-4

EC Name:

2-ethylhexyl mercaptoacetate

Cas Number:

7659-86-1

Molecular formula:

C10H20O2S

IUPAC Name:

2-ethylhexyl 2-sulfanylacetate

Details on test material:

- Name of test material (as cited in study report): 2-Ethylhexyl Thioglycolate
- Physical state: Liquid at RT, Colorless
- Analytical purity: 99.90%
- Density: 0.974 g/ml (20¿)
- Vapor Pressure: 0.01 hPA(20 ¿)
- Lot/batch No.: 26.05.08.D
- Expiration date of the lot/batch: May 2010
- Storage condition of test material: In original container, at room temperature (10 - 30 ¿), in the dark

Test organisms

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Test System Species/Origin: Activated sludge, micro organisms from a domestic waste
water treatment plant was supplied by the municipal sewage treatment plant Darmstadt, Germany.
Conditioning: The activated sludge was washed by centrifugation and the supernatant liquid phase was decanted, The solid material was resuspended in tap water and again centrifuged, The latter procedure was repeated three times, The washed sludge was resuspended in tap water and sewage feed (50 mL per L, see was added, The sludge was kept at room temperature under continuous aeration until use for two days. To this mix-ture, 50 mL synthetic sewage feed per litre was added daily, starting three days prior to use, and the sludge was kept at room temperature under continuous aeration until use, Immediately before use, the dry weight of the activated sludge was determined, and diluted to 3,8 giL with tap water. The pH of the activated sludge was 7,6 and therefore no adjustment was necessary.

Study design

Test type:

static

Water media type:

freshwater

Total exposure duration:

180 min

Test conditions

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Results and discussion

Effect concentrations

Effect concentrations 1

Duration:

180 min

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Effect concentrations 2

Duration:

180 min

Dose descriptor:

NOEC

Effect conc.:

> 100 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

Inhibition of Respiration Rate: The influence of 2-Ethylhexyl Thioglycolate on the respiration rate of activated sludge is presented in Table 2. In comparison to the inoculum controls the respiration rate of the activated sludge was slightly inhibited by 5,1 % and 7,7% % at the nominal concentrations from 1 to 32 mg/L, respectively. At the highest nominal concentration of 100 mg/L, the respiration rate was moderately inhibited by 15.4%, respectively, Test item concentrations exceeding 100 mg/L were not tested.

3-Hours EC20 and 3-hours EC50: Based on measured inhibition rates, no 3-hour EC20 and EC50 could be quantified because up to the highest nominal test concentration of 100 mg/L less than 20 % inhibition was noted after three hours incubation, Nevertheless, the 3-hour EC20 and EC50 are clearly higher than 100 mg/L under the present test conditions.

Results with reference substance (positive control):

Inhibition of Respiration Rate: The inhibition of the activated sludge treated with the reference item was in the range of 20% to 80 % for the test concentrations of 3,2, 10 and 32 mg/L.

3-Hours EC50 of 3,5-Dichlorophenol: The 3-hour EC10, EC20 and EC50 and their 95 % confidence limits of 3,5-Dichlorophenol were calculated. The results are listed below in Table 3.

Any other information on results incl. tables

 

 

 

Table 2.   Influence of 2~Ethylhexyl Thioglycolate and the Reference Item 3,5-Dichlorophenol on
	Oxygen Consumption of Activated Sludge
Flask	Treatment	Concen-	Oxygen	Inhibition	pH-values		Oxygen
No.		tration	consumption				concentration
							[mg O2/L]
		[mg/L]	[mg O2/L min]	%	start*	end*	start*	end*
1	control	---	0.42	---	7.4	8.0	7.7	8.2
10	control	---	0.36	---	7.4	7,9	7.6	8.0
			--
		mean	0.39
	% replicate deviation		7,7
2	3,5-DCP	32	0.09	76,9	7.4	7,9	7.6	8.3
3	3,5-DCP	10	0.20	48,7	7.4	7.9	7.5	8.0
4	3,5-DCP	3.2	0.31	20,5	7.4	7.9	7.5	8.1
	-
5	Test item	100	0.33	15.4	n. d.	8.0	n. d,	8.0
6	Test item	32	0.37	5.1	n. d.	7,9	n. d,	8.0
7	Test item	10	0.37	5.1	n. d.	7.9	n. d.	8.1
8	Test item	3.2	0,37	5,1	n. d.	7,9	n. d.	8.1
9	Test item	1	0,36	7,7	n. d.	7,9	n. d,	8.0
*: Start and end of 3-hour aeration
n. d.: not determined due to the volatility of the test item
DCP: 3,5-Dichlorophenol
Test item: 2-Ethylhexyl Thioglycolate

 

 

 

 

 

 

Table 3: Summary of EC₁₀, EC₂₀, and EC₅₀-values with 3,5-Dichlorophenol.

 

Parameter	EC10	EC20	EC50
Value [mgll]	1.6	3.1	10,6
lower 95%-cl	0,9	2.1	8.8
upper 95%-cl	2.3	4.1	12,8

 

 

The following nominal concentrations of the positive control 3,5 Dichlorophenol were tested on the same activated sludge and under identical conditions as the test item: 32, 10 and 3.2 mg/L. In comparison to the controls the respiration rate of the activated sludge was moderately inhibited by 20.5% at the lowest nominal concentration of 3.2 mg/L. At the nominal concentrations of 10 and 32 mg test item/L, the respiration  ate was inhibited by 48.7% and 76,9%, respectively.

 

Applicant's summary and conclusion

Executive summary:

The influence of the test item 2-Ethylhexyl Thioglycolate on the activity of activated sludge was evaluated by measuring the respiration rate under defined conditions. The respiration rate (oxygen consumption) of an aerobic activated sludge fed with a standard amount of synthetic sewage was measured in the presence of various concentrations of the test item after an incubation period of 3 hours, according to the OECD Guideline 209.

 

In comparison to the inoculum controls the respiration rate of the activated sludge in presence of the thest item 2-Ethylhexyl Thioglycolate was slightly inhibited by 5,1 % and 7,7% % at the nominal concentrations from 1 to 32 mg/L, respectively. At the highest nominal concentration of 100 mg/L, the respiration rate was moderately inhibited by 15.4%, respectively, Test item concentrations exceeding 100 mg/L were not tested.

 

Based on measured inhibition rates, no 3-hour EC₂₀ and EC₅₀  could be quantified because up to the highest nominal testitem  concentration of 100 mg/L less than 20 % inhibition was noted after three hours incubation. Nevertheless, the 3-hour EC₂₀ and EC₅₀ are clearly higher than 100 mg/L under the present test conditions.

 

The inhibition of the respiration rate in the presence the positive test control item 3,5-Dichlorophenol was in the range of 20% to 80 % for the test concentrations of 3,2, 10 and 32 mg/L.  The 3-hour EC₁₀, EC₂₀ and EC₅₀ and their 95 % confidence limits of 3,5-Dichlorophenol were calculated and found to 1.6, 3.1, and 10.6 mg/L, repectively.