L-(+)-lactic acid

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1991-09-06 to 1992-03-30

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

yes

Remarks:

The test method was modified to involve a better buffered medium (150 mg/L NaHCO3) and the use of a parametric model to calculate the effect concentrations.

GLP compliance:

yes

Specific details on test material used for the study:

80% Lactic acid solution in water. Batch no. ZO 3456

Analytical monitoring:

yes

Details on sampling:

- Concentrations: Samples were taken at t = 0 and 72 h from 0, 0.1, 1.0 and 2.8 g/L nominal concentrations
- Sampling method: 250 mL bottles
- Sample storage conditions before analysis: Each sample was analysed twice (on October 02 and November 02, 1991); the samples were stored in a refrigerator prior to analysis.

Vehicle:

no

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

The freshwater green alga Selenastrum capricornutum (ATCC 22662), which belongs to the order of Chlorococcales (class Chlorophyceae), was used as the test organism. The culture was supplied by the 'American Type Culture Collection', c/o Sales Department, 12301 Parklawn Drive, Rockville, MD 20852, USA.
A pre-culture of algae in the exponential growth phase was prepared as detailed in OECD guideline no. 201, using an appropriate medium.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Post exposure observation period:

None

Hardness:

No data

Test temperature:

No data

pH:

Ca. 8

Dissolved oxygen:

No data

Salinity:

Not applicable, freshwater species

Conductivity:

No data

Nominal and measured concentrations:

Nominal (test material): 0, 0.1, 0.33, 0.56, 1.0, 1.9 and 2.8 g/L
Nominal (lactic acid): 0, 0.08, 0.26, 0.45, 0.8, 1.72, 2.24 g/L
Actual (lactic acid): <0.005, 0.020–0.065, 0.44–0.62, 1.45–1.74 g/L (for 0, 0.1, 1.0 and 2.8 mg/L nominal concentrations)

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type (delete if not applicable): closed
- Initial cells density: 0.9e+04 cells/mL
- Control end cells density: 156.0e+04 cells/mL
- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates): 4

GROWTH MEDIUM
- Standard medium used: Yes

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: Electronic particle counter

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 1.8
- Range finding study
- Test concentrations: 0, 0.1, 1.0, 10, 101 and 1008 mg/L
- Results used to determine the conditions for the definitive study: Yes

Reference substance (positive control):

not required

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

> 533 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

ca. 1.9 g/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

ca. 3.5 g/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95 % CI = 2.8-4.4

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 2.8 g/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Details on results:

By visual comparison of the measured and the calculated growth curves of algal suspensions exposed to the test substance with those of the algal controls the no-observed-effect-concentration (NOEC) of the 80 % aqueous solution of L(+)-lactic acid was estimated to be 1.9 g/L.
Microscopic examination of the cells at the start and end of the incubation period revealed no abnormalities, however many bacteria were found in the cultures exposed to test substance concentrations of 1.0, 1.9 and 2.8 g/L.
The pH of the algal medium containing different test substance concentrations was adjusted to the range pH 7.5-8.0 at the start of the test. It was found to remain constant (pH 8.0-8.1) during the test. In the presence of algae the pH was found to slightly increase with algal cell density (pH 8.2-8.7).

Validity criteria fulfilled:

yes

Conclusions:

The NOEC of lactic acid (pH adjusted to approximately 8) to green algae is higher than 533 mg/L actual concentration of lactate (TWA).

Executive summary:

In a 72 hour acute toxicity study, cultures of Selenastrum capricornutum (ATCC 22662) were exposed to L(+) lactic acid (80 %) at nominal concentrations of 0, 0.10, 0.33, 0.56, 1.0, 1.9 and 2.8 g/L under static conditions in accordance with the OECD 201 guideline. The NOEC and EC50 values based on growth rate were 1.9 g/L and 3.5 g/L, respectively. There were no compound related phytotoxic effects. This toxicity study is classified as acceptable and satisfies the guideline requirements for alga growth inhibition study with S. capricornutum.

Results synopsis

Test organism: Selenastrum capricornutum

Test type: Static

72-hr E_bC₅₀: > 2.8 g/L (95% C.I.: 2.24–3.52 g/L), in terms of lactic acid

72-hr NOEC: > 533 mg/L, in terms of lactic acid

Endpoint(s) effected: Growth, abnormalities of the cells

An effect on the inoculum viability, as found in this test, may be expected when a substance loses its toxicity during the test, in this case probably due to biodegradation. The concentrations quoted in this report are the nominal concentrations of the test substance (a solution of about 80 % L(+) lactic acid) as supplied by sponsor. At the start of the test 65–82 % of the nominal test substance concentrations were found by chemical analysis. At the end of the test the concentrations were considerably lower: 15, 57 and 73 % at the three concentrations analysed. The actual concentrations of lactic acid tested at the start of the test were < 0.005, 0.020–0.065, 0.44–0.62, 1.45–1.74 g/L. According to the calculated time-weighted mean (see formula below from the OECD guideline 211: TWM = (conc0 – conc1)/(LN(conc0) – (LN(conc1))) the concentrations which should be used for effect calculations are 31 mg/L, 533 mg/L, and 1620 mg/L. The EC50 and the NOEC from the test report have to be regarded as invalid, as they were calculated on the basis of nominal values. Concerning the NOEC of 1.9 g/L, the replicates with the test concentration of 1.9 g/L were not verified analytically. Therefore, no conclusion on the actual concentration can be drawn. However, the next lower concentration was assessed analytically, revealing that the NOEC is above 533 mg/L (time-weighted mean of the measured lactic acid concentration).

Description of key information

NOEC 72 h > 533 mg/L (measured TWA)

Experiments were performed in buffered solutions; i.e., the adjusted pH of the algal medium containing different test substance concentrations (pH 7.5–8.0 at the start of the test) remained largely constant (pH 8.0–8.1, pH 8.2–8.7 in the presence of algae) during the tests. Effects can be therefore assigned to the test substance and are not confounded with pH effects due to the acidity of lactic acid.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

533 mg/L