Sodium mercaptoacetate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to microorganisms, other

Remarks:

toxicity control performed during biodegradation screening test

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

May 11, 2021 - June 08, 2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Version / remarks:

1992

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Aerobic activated sludge, microorganisms from a domestic waste water treatment plant was supplied by the sewage treatment plant Rossdorf, Germany.

The aerobic activated sludge used for this study was deposited for 15 min, washed by centrifugation and the supernatant liquid phase was decanted. The solid material was re-suspended in test water and centrifuged again. This procedure was done three times. An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight was determined. Based on this ratio, calculated aliquots of washed sludge suspension,
corresponding to 3.5 g dry material per litre were mixed with test water and aerated overnight. This suspension was used for the experiment.

Test type:

static

Water media type:

freshwater

Total exposure duration:

28 d

Nominal and measured concentrations:

102.1 mg/L

Details on test conditions:

TEST CONDITIONS
- Composition of medium:
Reconstituted Test Water: Analytical grade salts were added to ultrapure water to prepare the following stock solutions:
a) 4.25 g KH2PO4, 10.88 g K2HPO4, 16.7 g Na2HPO4 x 2 H2O, 0.25 g NH4Cl filled up with pure water to 500 mL volume; the pH-value was 7.4.
b) 11.25 g MgSO4 x 7 H2O filled up with pure water to 500 mL volume
c) 18.2 g CaCl2 x 2 H2O filled up with pure water to 500 mL volume
d) 0.125 g FeCl3 x 6 H2O filled up with pure water to 500 mL volume
In order to avoid precipitation of iron hydroxide in the stock solution d), one drop of concentrated HCl per litre was added before storage.
50 mL of stock solution a) and 5 mL of the stock solutions b) to d) were combined and filled up to a final volume of 5000 mL with ultrapure water. The pH was 7.6.

- Additional substrate: no
- Test temperature: 22°C ± 1°C
- pH: 7.5 (measured at the start of the test) / 6.9 to 7.4 (measured at the end of the test)
- pH adjusted: no
- final sludge concentration in test flasks: 28.7 mg sludge/L
- Continuous darkness: yes


TEST SYSTEM
- Culturing apparatus: Manometric Test System with test flasks containing a volume of approximately 500 mL
The pressure decrease in the reaction vessels was measured over complete experimental phase of 28 days using the BSB-Sensomat-System©. The test flasks were closed
gas-tight by a measuring head. Potassium hydroxide solution (45%) was used for trapping the produced carbon dioxide. The amount of O2 consumed by the activated sludge was calculated from the decrease of pressure in the reaction vessel.
- Number of culture flasks/concentration: 2

SAMPLING
- Sampling frequency: continuous measurement


CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Abiotic sterile control: yes
- Toxicity control: yes

Key result

Duration:

14 d

Dose descriptor:

IC0

Effect conc.:

>= 102.1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Executive summary:

The test item NaTG was investigated for its ready biodegradability in a manometric respirometry test over a period of 28 days in accordance with OECD Guideline 301F. The
biodegradation was followed by the oxygen uptake of the microorganisms during exposure. As a reference item sodium benzoate was tested simultaneously under the same conditions as the test item, and functioned as a procedure control.

A mean biodegradation of 10% or more of the test item was reached at day 5, the mean degradation was 39.5%. At the end of the 10-day window at day 15, the mean degradation was 65% and therefore the 10 day window criterion was passed. The mean biodegradation at test end after 28 days was 84.5%. The degradation rate 98% did reach 60% within the 10-day window and after 28 days. Therefore, the test item is considered to be readily biodegradable.

The reference item sodium benzoate was sufficiently degraded to 79% after 14 days and to 89% after 28 days of incubation, thus confirming the suitability of the aerobic activated sludge inoculum used.

In the toxicity control containing both, the test item and the reference item sodium benzoate, 76% biodegradation was noted within 14 days and 84% biodegradation after 28 days of incubation. According to the test guidelines, the test item can be assumed to be not inhibitory to the aerobic activated sludge microorganisms because
degradation was >25% within 14 days.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

100 mg/L

Additional information

The test item NaTG was investigated for its ready biodegradability in a manometric respirometry test over a period of 28 days in accordance with OECD Guideline 301F. The biodegradation was followed by the oxygen uptake of the microorganisms during exposure. As a reference item sodium benzoate was tested simultaneously under the same conditions as the test item, and functioned as a procedure control.

A mean biodegradation of 10% or more of the test item was reached at day 5, the mean degradation was 39.5%. At the end of the 10-day window at day 15, the mean degradation was 65% and therefore the 10 day window criterion was passed. The mean biodegradation at test end after 28 days was 84.5%. The degradation rate 98% did reach 60% within the 10-day window and after 28 days. Therefore, the test item is considered to be readily biodegradable.

The reference item sodium benzoate was sufficiently degraded to 79% after 14 days and to 89% after 28 days of incubation, thus confirming the suitability of the aerobic activated sludge inoculum used.

In the toxicity control containing both, the test item and the reference item sodium benzoate, 76% biodegradation was noted within 14 days and 84% biodegradation after 28 days of incubation. According to the test guidelines, the test item can be assumed to be not inhibitory to the aerobic activated sludge microorganisms because degradation was >25% within 14 days.