L-cystine dihydrochloride

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
No study with the target substance L-cystine dihydrochloride is available. However a study with L-cysteine hydrochloride is available and considered reliable. Since L-cysteine and L-cystine can be formed from one in the other, L-cysteine hydrochloride is considered to be a suitable source substance for read-across purpose.

2. SOURCE AND TARGET CHEMICAL(S)
No further information.

3. ANALOGUE APPROACH JUSTIFICATION
Experimental data for toxicity to aquatic algae are available for L-cysteine hydrochloride. The study was conducted according to OECD guideline 201. This GLP study is considered reliable and well documented. Under oxidative conditions two L-cysteine molecules form disulfide bonds L-cystine is formed. In the available study both substances were analytical determined. Measurements showed that over time the concentration of L-cysteine decreased and L-cystine increased. The result presents the combined toxicity of both substances. Therefore, the information of the available study is considered to be sufficient to cover the required endpoint information for the target substance L-cystine dihydrochloride.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

40.1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

7.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

10.3 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

3.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

01.08.2016 to 31.10.2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

Chemical analysis of the test item concentrations and control were performed daily (at the start of the test and after 24, 48 and 72 h). Samples were taken and deep-frozen. Before freezing, the algae were sepatated from the medium by centrifugation at a low g-force (4000g for 20 min).

Vehicle:

no

Details on test solutions:

A stock solution of 100 mg/L was freshly prepared by stirring the solution for 60 minutes with a magnatic stirrer.

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM
- Common name: Desmodesmus subspicatus
- Strain: 86.81 SAG
- Source: Pflanzenphysiologisches Institut der Universität Göttingen, Germany
- Method of cultivation: Algae were cultivated in air-conditioned room with a water temperature of 21.0 - 24.0°C, controlled at ± 2°C. 300 mL Erlenmeyer flasks filled with 100 mL algae suspension were covered with air permeable stoppers. The cultures were shaken continously at ca. 120 rpm and lit between 4440 and 8880 lux.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

not specified

Test temperature:

23.0 - 24.4°C

pH:

7.88 - 8.00

Dissolved oxygen:

not specified

Salinity:

not applicable

Conductivity:

not specified

Nominal and measured concentrations:

Nominal concentrations: 1.0, 3.2, 10.0, 31.6 and 100 mg/L
Recoveries were between 81 - 99% and therefeore, endpoints are based on nominal concentrations.

Details on test conditions:

TEST SYSTEM
- Test vessel: flask
- Type: open system
- Medium volume per flask: 100 mL
- Initial cells density: 10^4 cells/mL
- Control end cells density: 217×10^4 cells/mL (mean value)
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes (OECD medium according to OECD 201)

OTHER TEST CONDITIONS
- Photoperiod: continuously
- Light intensity and quality: 8167 to 8218 lux, fluorescent lamps

EFFECT PARAMETERS MEASURED:
- Determination of cell concentrations: electronic particle counter
- Morphological Changes of Algal Cells: microscopy

TEST CONCENTRATIONS
- Range finding study: no

Reference substance (positive control):

yes

Remarks:

Potassium dichromate, test period: 09–12 May 2016

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

40.1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

7.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

10.3 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

3.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Details on results:

No morphological changes of the treated algae in comparision to the control algae were observed.

Results with reference substance (positive control):

The 72h ErC50: 0.72 mg/L (95 % confidence limits: 0.70 – 0.74 mg/L). The 72h EyC50: 0.40 mg/L (95 % confidence limits: 0.38 – 0.42 mg/L)

Reported statistics and error estimates:

For the determination of the ECx values Probit analysis was used.
Statistical software: ToxRat (ToxRat Professional Version 2.10, ToxRat Solutions GmbH, Alsdorf, Germany)

Validity criteria fulfilled:

yes

Conclusions:

In this 72-h algal growth inhibition test the effects of the test item on the growth of Desmodesmus subspicatus was determined. The algal growth in relation to a control culture was determined over a fixed test period of 72 hours.The 72-h EC10, EC20, EC50 for growth were determined to be 7.5, 13.4 and 40.1 mg/L, respectively. The 72-h EC10, EC20, EC50 for yield were determined to be 3.6, 5.1 and 10.3 mg/L, respectively.

Executive summary:

The purpose of this study was to determine the effect of the test item on the growth of a the green algal species Desmodesmus subspicatus. Exponentially growing cultures of Desmodesmus subspicatus were exposed to test item concentrations of 1.0, 3.2, 10.0, 31.6 and 100 mg/L. The algal growth in relation to a control culture was determined over a fixed test period of 72 hours.The 72-h EC10, EC20, EC50 for growth were determined to be 7.5, 13.4 and 40.1 mg/L, respectively. The 72-h EC10, EC20, EC50 for yield were determined to be 3.6, 5.1 and 10.3 mg/L, respectively.

Description of key information

The effect of the test item on the growth of a unicellular green algal species Desmodesmus subspicatus was determined according to OECD 201, Regulation (EC) No. 226/2016 Method C.3 under GLP (reference 6.1.5-1). The study was conducted under static conditions with an initial cell density of 1x10^4 cells/mL for a period of 72 hours. The EC50 and EC10 based on growth rate were determined to be 40.1 mg/L and 7.5 mg/L, respectively.

Key value for chemical safety assessment

EC50 for freshwater algae:

40.1 mg/L

EC10 or NOEC for freshwater algae:

7.5 mg/L

Additional information

No data for toxicity for aquatic algae for the target substance L-cystine dihydrochloride were available. Therefore read across was performed.

The effect of the source substance on the growth of the green algal species Desmodesmus subspicatus was determined according to OECD 201, Regulation (EC) No. 226/2016 Method C.3 under GLP (reference 6.1.5-1). The study was conducted under static conditions with an initial cell density of 1x10^4 cells/mL for a period of 72 hours. Five concentrations were tested in a geometrical series: 1.0, 3.2, 10.0, 31.6 and 100 mg/L.The EC50 values for inhibition of growth rate (ErC50) was 40.1 mg/L and for inhibition of yield (EyC50) 10.3 mg/L. The EC10 value was determined to be 7.5 mg/L based on growth rate (ErC10) and 3.6 mg/L based on yield (EyC10).