3-mercaptopropionic acid

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:

2009-04-29

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

Deviations:

yes

Remarks:

adaptions of the guideline due to the properties of the test item (see "details on test conditions")

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Deviations:

yes

Remarks:

adaptions of the guideline due to the properties of the test item (see "details on test conditions")

GLP compliance:

yes (incl. QA statement)

Remarks:

Hess. Ministerium fuer Umwelt, laendlichen Raum und Verbraucherschutz, 65189 Wiesbaden, Germany

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

Appropriate amounts of test item were directly weight into the test vessels and test water was added. The composition was stirred intensively.

Test organisms (species):

activated sludge, domestic

Details on inoculum:

Activated sludge, micro organisms from a domestic waste water treatment plant was supplied by the municipal sewage treatment plant Darmstadt, Germany.
- Laboratory culture:
- Method of cultivation:
- Preparation of inoculum for exposure:
- Pretreatment:
- Initial biomass concentration: 3.3 g/L

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

20-21°C during pre-incubation (3 hours);
19-22°C during evaluation period

pH:

of activated sludge inoculum suspension: 7.6;
during experiment: see "remarks on results..."

Dissolved oxygen:

see "remarks on results..."

Nominal and measured concentrations:

test item: 10, 32, 100, 320, and 1000 mg test item/L (nominal)
reference compound (positive control; 3,5-Dichlorophenol): 3.2, 10, and 32 mg/L
two inoculum controls

Details on test conditions:

The test item 3-mercaptopropionic acid is a concentrated acid with strong vapour and therefore the test conditions according to the OECD 209 test guideline are not applicable. A modified test design was used to fulfil first the requirements of the OECD 209 and second the strong vapour character of the test item. The activated sludge micro organisms were exposed to the test item for three hours in a closed system with a headspace of air and intensively mixing. This type of study is recognized by the OECD and EEC guidelines and provides a rational basis to assess the respiration inhibition properties of the test item when incubated with activated sludge.

TEST SYSTEM
- Test vessel:
- Type: closed
- Material, size, headspace: glass flasks of approx. 1 L and Karlsruher flasks of 250 mL volume
- Fill volume: 200 mL
- Aeration: compressed air (approx. 0.8 L/min)
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2
- No. of vessels per vehicle control (replicates): no vehicle used
- Biomass loading rate: 1.32 g activated sludge dry weight/L


OTHER TEST CONDITIONS
- Adjustment of pH: not necessary


EFFECT PARAMETERS MEASURED : respiration inhibition


TEST CONCENTRATIONS
- Spacing factor for test concentrations: 3.2

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

393.3 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: 95% CL: 218.6-910.6 mg/L

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

32.1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: 95% CL: 2.7-77.4 mg/L

Duration:

3 h

Dose descriptor:

other: EC20

Effect conc.:

76.1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: 95% CL: 15.0-147.6 mg/L

Results with reference substance (positive control):

results calculated for the 3 h incubation period: EC10 = 3.4 mg/L; EC20 = 5.1 mg/L; EC50 = 11.4 mg/L
(95% CL could not be determined due to mathematical reasons)

Reported statistics and error estimates:

The 3-h ECx including the 95% confidence limits of the test item and reference item were calculated by Probit analysis.

Table 1. Influence of 3-mercaptopropionic acid and the Reference Item 3,5-Dichlorophenol on Oxygen Consumption of Activated Sludge

Flask no.	Treatment	Concentration	O2-consumption	Inhibition	pH values		O2 concentration
		[mg/L]	[mg O2/ L*min]	[%]	start*	end*	start*	end*
1	Control**	--	0.38	--	7.1	7.7	7.8	8.2
10	Control**	--	0.41	--	7.1	7.7	7.5	8.0
2	3,5-DCP	32	0.08	80.0	7.1	7.7	7.9	8.0
3	3,5-DCP	10	0.19	52.5	7.1	7.7	7.7	8.1
4	3,5-DCP	3.2	0.41	-2.5	7.1	7.8	7.7	8.1
5	Test item	1000	0.13	67.5	4.8	5.8	7.0	7.9
6	Test item	320	0.22	45.0	6.2	6.9	7.2	7.8
7	Test item	100	0.27	32.5	6.4	7.2	7.2	7.8
8	Test item	32	0.38	5.0	6.9	7.7	7.0	8.0
9	Test item	10	0.40	0.0	7.0	7.7	7.1	7.8

* Start and end of 3-hour aeration

** mean value of oxygen consumption of the 2 controls: 0.40 mg O2/L*min; % replicate deviation (CV): 5.3.

3,5-DCP: 3,5-Dichlorophenol

Test item: 3-mercaptopropionic acid

Negative inhibition values: enhancement of respiration

 

Table 1 shows the influence of 3-mercaptopropionic acid on the respiration rate of activated sludge. In comparison to the inoculums controls the respiration rate of the activated sludge was not or slightly inhibited by 0 and 5% at the two lowest concentrations of 10 and 32 mg/L, respectively. At the next higher nominal concentrations of 100 and 320 mg/L, the respiration rate was moderately inhibited by 32.5 and 45%, respectively. At the highest nominal test concentration of 1000 mg/L an inhibition rate of 67.5% was found. Test item concentrations exceeding 1000 mg/L were not tested.

 

Based on measured inhibition rates, the 3-hour EC10, EC20 and EC50 and their 95% confidence limits were determined as follows (all values in mg/L):

Parameter	EC10	EC20	EC50
Value	32.1	76.1	393.3
Lower 95%-CL	2.7	15.0	218.6
Upper 95%-CL	77.4	147.6	910.6

 

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: 3.2, 10 and 32 mg/L. In comparison to the controls the respiration rate of the activated sludge was not inhibited at the lowest nominal concentration of 3.2 mg/L (-2.5%). At the nominal concentrations of 10 and 32 mg/L test item/L, the respiration rate was inhibited by 52.5 and 80%, respectively. For more details on the results see Table 1.

 

The 3-hour EC10, EC20 and EC50 of 3,5-Dichlorophenol were calculated (see below). The corresponding 95% confidence limits could not be determined due to mathematical reasons (n.d.).

Parameter	EC10	EC20	EC50
Value	3.4	5.1	11.4
Lower 95%-CL	n.d.	n.d.	n.d.
Upper 95%-CL	n.d.	n.d.	n.d.

 

Furthermore, Table 1 is providing information on the determined oxygen concentrations and pH values as well as for the calculated oxygen consumption rates.

 

All validity criteria for OECD test guideline 209 were met.

Validity criteria fulfilled:

yes

Conclusions:

EC10 = 32.1, EC20 = 76.1, and EC50 = 393.3 mg/L

Executive summary:

The influence of the test item 3-mercaptopropionic acid on the activity of activated sludge was evaluated by measuring the respiration rate under defined conditions in a study according to OECD Guideline for Testing of Chemicals, Section 2, No. 209: “Activated Sludge, Respiration Inhibition Test",
adopted April 04, 1984.. 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.

In comparison to the inoculum controls the respiration rate of the activated sludge was not or only slightly inhibited by 0 and 5% at the two lowest nominal concentrations of 10 and 32 mg/L, respectively. At the next higher nominal concentrations of 100 and 320 mg/L, the respiration rate was moderately inhibited by 32.5 and 45%.

At the highest nominal test concentration of 1000 mg/L an inhibition rate of 67.5% was found.
The resulting inhibitions of the respiration rates based on nominal concentrations of the test item were EC10 = 32.1, EC20 = 76.1, and EC50 = 393.3 mg/L, respectively.

Description of key information

EC50 (3 h) = 393.3 mg/L (activated sludge);
EC10 (3 h) = 32.1 mg/L (activated sludge)

Key value for chemical safety assessment

EC50 for microorganisms:

393.3 mg/L

EC10 or NOEC for microorganisms:

32.1 mg/L

Additional information

The influence of the test item 3-mercaptopropionic acid on the activity of activated sludge was evaluated by measuring the respiration rate under defined conditions in a study according to OECD Guideline for Testing of Chemicals, Section 2, No. 209: “Activated Sludge, Respiration Inhibition Test",
adopted April 04, 1984.. 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.

In comparison to the inoculum controls the respiration rate of the activated sludge was not or only slightly inhibited by 0 and 5% at the two lowest nominal concentrations of 10 and 32 mg/L, respectively. At the next higher nominal concentrations of 100 and 320 mg/L, the respiration rate was moderately inhibited by 32.5 and 45%.

At the highest nominal test concentration of 1000 mg/L an inhibition rate of 67.5% was found.
The resulting inhibitions of the respiration rates based on nominal concentrations of the test item were EC10 = 32.1, EC20 = 76.1, and EC50 = 393.3 mg/L, respectively.