Histidine

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:

2015-10-16 to 2016-03-03

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:

no

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations: control, 4.6, 10, 22, 46, 100 mg/L
- Sampling method: at test start, after 24h, 48h and 72h

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Stock solution: 100 mg/L in nutrient medium and dilution of stock solution with nutrient medium for lower concentrations.

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM
- Strain: SAG strain 86.81
- Source: MBM Sciencebridge GmbH (Institut für Pflanzenphysiologie of Universität Göttingen)
- The algae are kept as stock culture on solid agar at 2 - 8 °C. From the stock culture, a permanent culture was prepared. From an aliquot of the permanent culture, the pre-culture was prepared.
- Method of cultivation: 3 days before start of test, permanent culture brought into nutrient medium under continuous lighting for 72 h. The resulting culture grew exponentially.
- Any deformed or abnormal cells observed: check for absence of cell aggregates via photometric measurements

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Post exposure observation period:

none

Test temperature:

21.9-23.3°C

pH:

8.2 at start of experiment
ranging from 7.4 to 8.2 at end of experiment

Nominal and measured concentrations:

Nominal concentrations: 4.6, 10, 22, 46, 100 mg/L
Measured concentrations: 95-109 % of nominal concentration. Because the solutions became turbid during the test, test item was removed by membrane filtration before measurement. After 72h no test item detectable in filtrate. More details in results section.
Because the good correlation between nominal and measured concentrations (at test start), nominal concentrations were used to express results.

Details on test conditions:

TEST SYSTEM
- Vessels: glass flasks total volume 65 mL
- Type: open, perforated plastic foil
- Initial cells density: 2900 cells/mL
- Control end cells density: 5*10^5 cells/mL
- No. of vessels per concentration: 2 replicates
- No. of vessels per control: 2 replicates

GROWTH MEDIUM
- Standard medium used: yes

OTHER TEST CONDITIONS
- Adjustment of pH: 8.2
- Photoperiod: continuous
- Light intensity and quality: 5300 Lux

EFFECT PARAMETERS MEASURED:
- Determination of cell concentrations: photometric measurement of optical density

TEST CONCENTRATIONS
- Test concentrations: 4.6, 10, 22, 46 and 100 mg/L

Reference substance (positive control):

yes

Remarks:

potassium dichromate

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

4.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Yield

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

22 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Yield

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

58 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 55-62 mg/L

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

31 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Yield

Remarks on result:

other: 30-33 mg/L

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

74 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Yield

Remarks on result:

other: 69-80 mg/L

Details on results:

Validity criteria were met.

Results with reference substance (positive control):

growth rate: 72h EC50 = 0.80 mg/L (0.76-0.85 mg/L)
Yield: 72h EC50 = 0.36 mg/L (0.35-0.38 mg/L)

Reported statistics and error estimates:

Software used: ToxRat®Professional

Analytical determination

The start concentration was measured directly. As the test media became turbid during the experiment, other samples were analysed after membrane filtration.

nominal concentration (mg/L)	measured concentration at 0h	% of nominal concentration	measured concentrations (mg/L)
			24h	48h	72h
0	nd	-	nd	nd	nd
4.6	5.02	109	4.5	nd	nd
10	9.47	98	9.32	nd	nd
22	21.16	96	21.25	1.39	nd
46	45.63	99	46.44	6.23	nd
100	97.96	98	99.74	19.54	nd

nd = not detectable

Turbidity was observed, however, since this turbidity was not observed in the acute Daphnia test, it can be concluded that the test item is stable in aqueous medium and the turbidity observed is caused by a reaction between test item and the ingredients of algal tesst medium. As a result, the test item could not be measured at the end of the experiment.

Results growth rate and yield

nominal concentration (mg/L)	growth rate (day-1)	% inhibition growth rate	Yield (cells/mL)	% inhibition yield
0	1.71	0.0	496197	0.0
4.6	1.72	-0.3	494440	0.4
10	1.72	-0.5	480773	3.1
22	1.69	1.4	478033	3.7
46	1.61	6.0	374100	24.6
100	1.31	23.5	162060	67.3

VALIDITY

- The cell concentration in blank control should increase by a factor 16 within 72 h. The observed value was 170.

- The mean coefficient of variation of daily growth rates was 17 % in blank controls, well below the allowed maximum of 35 %.

- The coefficient of variation of average growth rate during the whole test peroid was 1 %, well below the allowed maximum of 7%.

- The pH change of the blank control should not fluctuate more than 1.5 units. The maximal fluctuation observed was 0.8 units.

Validity criteria fulfilled:

yes

Conclusions:

L-Histidine was found to inhibit growth of green algae Desmodesmus subspicatus after 72h exposure. The EC50 values were > 100 mg/L and 74 mg/L for growth rate and yield respectively. The EC10 values found were 58 mg/L for growth rate and 31 mg/L for yield.

Executive summary:

The toxicity of L-histidine to green algae Desmodesmus subspicatus after 72 h exposure was assessed according to OECD 201. All validity criteria were met. In total, 5 concentrations were tested (4.6, 10, 22, 46 and 100 mg/L) in 2 replicates. Daily the cell number was assessed and inhibition of growth rate and yield was calculated. The results for the test item were:

Endpoint	NOEC	LOEC	EC10	EC50
	mg/L
Growth rate	10	22	58	> 100
Yield	4.6	10	31	74

Description of key information

L-Histidine was found to inhibit growth of green algae Desmodesmus subspicatus after 72h exposure. The EC50 values were > 100 mg/L and 74 mg/L for growth rate and yield respectively. The EC10 values found were 58 mg/L for growth rate and 31 mg/L for yield.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC10 or NOEC for freshwater algae:

58 mg/L

Additional information

For this study one key study is available in which the toxicity of L-histidine to green algae Desmodesmus subspicatus after 72 h exposure was assessed according to OECD 201. All validity criteria were met. In total, 5 concentrations were tested (4.6, 10, 22, 46 and 100 mg/L) in 2 replicates. Daily the cell number was assessed and inhibition of growth rate and yield was calculated. The results for the test item were:

Endpoint	NOEC	LOEC	EC10	EC50
	mg/L
Growth rate	10	22	58	> 100
Yield	4.6	10	31	74