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Toxicity to microorganisms

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Endpoint:
activated sludge respiration inhibition testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
For details and justification of read-across please refer to the read-across report attached to IUCLID section 13.
Reason / purpose for cross-reference:
read-across source
Analytical monitoring:
no
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).

This information is used in a read-across approach in the assessment of the target substance.For details and justification of read-across please refer to the read-across report attached to IUCLID section 13.

Endpoint:
activated sludge respiration inhibition testing
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:

Description of key information

Calcium (S)-lactate fully dissociates into Ca2+ ions and lactate. The ecotoxicology of Calcium (S)-lactate can be understood in terms of the ecotoxicology of calcium ions and lactic acid. Calcium ions are known as an essential nutrient for microorganisms; they are non-toxic. No inhibition of activated sludge respiration was observed for lactic acid 88.3 % at 100 mg/L. Thus, no toxic effects of Calcium (S)-lactate on STPs are expected.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
107 mg/L

Additional information

Calcium (S)-lactate fully dissociates into Ca2+ ions and lactate. The ecotoxicology of Calcium (S)-lactate can be understood in terms of the ecotoxicology of calcium ions and lactic acid. Calcium ions are known as an essential nutrient for microorganisms; they are non-toxic. 

Lactic acid does not inhibit activated sludge respiration at concentrations up to 100 mg/L test material (88.3 mg/L active substance). Inhibition was -1.1% (stimulation). Note that lactic acid is produced by certain micro-organisms in sewage treatment plants, and removed by other micro-organisms in the same 'ecosystem'. As such lactic acid is an ubiquitous and abundant natural component of active sewage treatment systems. No toxic effects of lactic acid on STPs are expected.

The NOEC respriation inhibition for Calcium (S)-lactate can be calculated from the NOEC for lactic acid: 88.3 × 1.21 = 107 mg Calcium (S)-lactate/L. Note that the NOEC for lactic acid, thus also the NOEC for Calcium (S)-lactate, is expected to be much higher because lactic acid is produced by certain micro-organisms in sewage treatment plants and removed by other micro-organisms in the same 'ecosystem'.

No toxic effects of Calcium (S)-lactate on STPs are expected.