L-(+)-lactic 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

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

GLP compliance:

yes

Specific details on test material used for the study:

88.2 % aqueous solution of lactic acid; batch no. 0602001247

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Municipal sewage treatment plant: 'Waterschap de Maaskant', 's-Hertogenbosch, the Netherlands, receiving predominantly domestic sewage.
The sludge was coarsely sieved, washed and diluted with ISO-medium. A small amount of the sludge was weighed and dried overnight at ca. 105 °C to determine the amount of suspended solids (4.3 g/L of sludge, as used for the test). The pH was 7.8 on the day of sampling and 7.5 on the day of testing. The batch of sludge was used one day after collection; therefore 50 mL of synthetic sewage feed was added per litre of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

18-18.6 °C

pH:

7.9

Dissolved oxygen:

7.7-7.8 mg/L

Nominal and measured concentrations:

100 mg/L test material nominal (88 mg/L active substance nominal).

Details on test conditions:

Type: other: Activated sludge respiration inhibition test
TEST SYSTEM
- Test vessel: All glass, approximately 300 ml oxygen bottles and 1 litre test bottles.

TEST MEDIUM / WATER PARAMETERS
Adjusted ISO medium, formulated using RO-water (tap-water purified by reverse osmosis; GEON Waterbehandeling, Berkel-Enschot, The Netherlands) with the following composition:
CaCI2.2H2O 211.5 mg/I
MgSO4.7H2O 88.8 mg/I
NaHCO3 46.7 mg/I
KCl 4.2 mg/I

SYNTHETIC SEWAGE FEED
16 g peptone 11 g meat extract
3 g urea
0.7 g NaCI
0.4 g CaCI2.2H2O
0.2 g MgS04.7H2O
2.8 g K2HP04
Dissolved in Milli-Q water, made up to 1 litre and filtered.
The pH was adjusted from 6.8 to 7.0 with 1 M NaOH (Merck, Darmstadt, Germany).

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
Oxygen consumption

TEST CONCENTRATIONS
Limit test

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 88.2 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: corrected for lactic acid content of the test material (88.2 %)

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 88.2 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: corrected for lactic acid content of the test material (88.2 %)

Results with reference substance (positive control):

- Results with reference substance valid? Yes
- Relevant effect levels: EC50 = 5.9 mg/L

Validity criteria fulfilled:

yes

Conclusions:

Lactic acid does not inhibit activated sludge respiration at concentrations up to 88.2 mg/L (corrected for lactic acid content of the test material). Inhibition was -1.1 % (i.e. slight stimulation).

Executive summary:

The influence of L-(+)-lactic acid on the respiration rate of activated sludge was investigated after a contact time of 3 hours. The study procedure was based on OECD guideline 209 (adopted April 4, 1984), EEC Directive 67/548 amended November 18, 1987 (87/302), Part C, Publication No. L133, adopted May 30, 1988 and ISO Standard 8192 (1986). The batch of the test material was a clear and colourless liquid (88.2 % aqueous solution of lactic acid) that could easily be mixed with water. A stock solution of 500 mg/L was prepared by adding 126.0 mg test substance to 250 ml of Milli-RO water. A stirring period of 30 minutes was used to accelerate dissolution and to ensure homogeneity. Volumes of the stock solution corresponding to the test concentration were then added to the test media. A concentration of 100 mg/L of the test material was tested in duplicate. Optimal contact between the test substance and test medium was ensured applying continuous aeration and stirring. No significant inhibition of the respiration rate of the sludge was recorded at 100 mg test material per litre. The duplicate measurement confirmed the result of the first measurement. Therefore no further testing was needed. Since all criteria for acceptability of the test were met, this study was considered to be valid. In conclusion, under the conditions of this present test, L-(+)-lactic acid was not toxic to waste water (activated sludge) bacteria at a concentration of 88.3 mg/L (corrected for lactic acid content of the test material).

Description of key information

A NOEC of 88.2 mg/L (lactic acid, 3 h) was determined with the parameter of total respiration inhibition, in accordance with the OECD guideline 209.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

88.2 mg/L