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Toxicity to aquatic algae and cyanobacteria

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Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study without detailed documentation
Qualifier:
according to guideline
Guideline:
other: "Hemmung der Zellvermehrung bei der Grünalge Scenedesmus subspicatus Chod." (Test Guideline of the German Environmental Protection Agency (UBA), May 1982)
GLP compliance:
not specified
Analytical monitoring:
not specified
Details on sampling:
No data.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method:
* thiourea was quantitatively dissolved in 800 ml double distilled water using a magnetic stirrer
* a dilution series was prepared from the stock solution (1 part stock solution in 2^0 to 2^8 parts mixture with double distilled water
* 6 replicates per concentration
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
TEST ORGANISM
- Scendesmus subspicatus Chodat (86.81 SAG)
- Source: laboratory, culture collection
- Age of inoculum (at test initiation): 72h
- Method of cultivation:
* stock cultures were cultivated in 20 mL nutrient solution (see field "Any other information on materials and methods incl. tables") in 100 mL Erlenmeyer flasks with metal caps
* continuous artificial illumination (Osram 40 W/30)
* 24 °C
* 50 % rel. humidity
* new stock cultures were prepared continuously every 10 days
- Pre-cultures:
* cultivated in 300 mL Erlenmeyer flasks closed with metal caps in 50 mL nutrient for test cultures (according to guideline)#
* cell density: 10^4/mL
* same light and temperature conditions as test
* cells of the precultures are used to inoculate the test cultures after 72 h

ACCLIMATION
- Acclimation period: 72 h
- Culturing media and conditions: same as test
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
96 h
Post exposure observation period:
Not applicable.
Hardness:
No data.
Test temperature:
24 +/- 1 °C
pH:
Measurements were conducted after 0, 24, 38, 72, and 96 h.
Dissolved oxygen:
No data.
Salinity:
not applicable
Nominal and measured concentrations:
Not reported.
Details on test conditions:
TEST SYSTEM
- Test vessel: 100 mL Erlenmeyer flasks with metal caps
- Type: closed
- Material, fill volume: glass, 20 mL
- Aeration: no
- Initial cells density: 10^4 cells/mL
- No. of vessels per concentration: 6
- Three parallel measurement were conducted.


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


OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: no
- Photoperiod: continuous illumination (fluorescent tube Osram L 25/40 W)


EFFECT PARAMETERS MEASURED:
- Determination of cell concentrations: optical density (opacity measurement: Eppendorf digital photometer 6155, filter 578 mm, 1 cm cuvette)


TEST CONCENTRATIONS
- no details on test concentrations reported
Reference substance (positive control):
yes
Duration:
96 h
Dose descriptor:
EC10
Effect conc.:
>= 0.5 - <= 0.7 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
cell number
Key result
Duration:
96 h
Dose descriptor:
EC50
Effect conc.:
>= 3.8 - <= 5.4 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
cell number
Details on results:
No further details reported.
Results with reference substance (positive control):
Potassium dichromate:
- 96-h EC10 = 0.45-0.5 mg/L
- 96-h EC50 = 1.35-1.45 mg/L
Validity criteria fulfilled:
yes
Conclusions:
The 96-h EC10 of thiourea for Scenedesmus subspicatus Chodat is in the range of 0.5-0.7 mg/L.
The 96-h EC50 of thiourea for Scenedesmus subspicatus Chodat is in the range of 3.8-5.4 mg/L.

Executive summary:

In a 96 hour acute toxicity study, the cultures of Scendedesmus subspicatus Chodat were exposed to thiourea at several concentrations (6 replicates per concentration, 3 parallel measurements) under static conditions in accordance with the Guideline of the German Environmental Protection Agnecy (UBA) of May 1982 (Hemmung der Zellvermehrung bei der Grünalge Scenedesmus subspicatus Chod.").


 


The EC10 and EC50 values based on cell density were 0.5 -0.7 mg/L and 3.8 -5.4 mg/L, respectively.


 


This toxicity study is classified as acceptable.


 


Results Synopsis:


Test Organism: Scenedesmus subspicatus Chodat


Test Type: Static


96-hr EC10: 0.5 -0.7 mg/L


96-hr EC50: 3.8 -5.4 mg/L


Endpoint effected: cell number

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
no data
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
documentation insufficient for assessment
Qualifier:
according to guideline
Guideline:
other: "Hemmung der Zellvermehrung bei der Grünalge Scenedesmus subspicatus Chod." (Test Guideline of the German Environmental Protection Agency (UBA), May 1982)
GLP compliance:
not specified
Analytical monitoring:
not specified
Details on sampling:
No details reported.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: A defined amount of thiourea was diluted in defined volume of sterilized double distilled water
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
TEST ORGANISM
- Scenedesmus subspicatus Chodat
- Source: Dr. Renate Kühn, Institute for Water, Soil and Air Hygiene, Federal Health Officem Berlin-Dahlem, FRG.
- Method of cultivation:
* Stock breeding conditions:
> algae stock cultures in 20 mL nutrient solution were stored in 100 mL Erlenmeyer flasks stoppered with metal caps (Kapsenberg-caps), placed on white surface, protected against daylight
> constant illumination (Philips fluorescent lamps, Type TL-D, 58 watts, 25 white universal)
> temperature: 21- 25 °C
> maintenance of test strain: fresh stock cultures were prepared every ten days (30 min steam sterilization of Erlenmeyer flasks containing 20 mL of nutrient solution, stoppered with metal caps; after cooling content was inoculated with 2 mL algae suspension from 10-say stock culture)

* Pre-culture:
> started 3 days prior to study initiation
> less than 1 part of algae suspension was taken from the stock culture and mixed with 1 part (vol.) of the concentrated nutrient medium and 8 parts (vol.) water
> total dilution up to 10 parts (made up by adding water
> cell concentration: approx. 10^4 cells/mL
> total volume: 50 mL
> incubation in 300 mL Erlenmeyer flasks with Kapsenberg caps for 3 days under same temperature and light conditions as those of the test cultures


ACCLIMATION
- Acclimation period: see pre-culture
- Culturing media and conditions: same as test
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
96 h
Post exposure observation period:
Not applicable.
Hardness:
No data.
Test temperature:
22 +/- 2 °C
pH:
no data
Dissolved oxygen:
no data
Salinity:
not applicable
Nominal and measured concentrations:
no data
Details on test conditions:
TEST SYSTEM
- Test vessel: 300 ml Erlenmeyer flasks stoppered with Kapsenberg caps
- Initial cells density: 10^4 cells/mL
- No. of vessels per concentration: 4
- two parallel dilution series
- first flask of each dilution series: 80 mL of saturated test chemical solution
- subsequnet dilutions: prepared by using a constant dilution ratio of 40 mL preliminary chemical dilution plus 40 ml double distilled water.
- subsequently 5 mL of medium and 5 mL of algae suspension of pre-culture were added to each flask of the dilution series (40 mL)

OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: no
- Photoperiod: continuous illumination
- Light intensity and quality: 120 µE/(m² s) (7.2 * 10^19 photons/(m² s))

EFFECT PARAMETERS MEASURED
- Observation intervals: 0, 72, and 96 hours
- Determination of cell concentrations: spectrophotometer (Zeiss PMQ II) at 578 nm
- Measured extinction values were convertes to cell numbers by use of a previously established standard curve
Reference substance (positive control):
not specified
Duration:
96 h
Dose descriptor:
EC10
Effect conc.:
>= 0.3 - <= 0.6 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: cell growth
Key result
Duration:
96 h
Dose descriptor:
EC50
Effect conc.:
>= 4.8 - <= 10 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: cell growth
Details on results:
No further results reported.
Results with reference substance (positive control):
No data.
Reported statistics and error estimates:
The relationship between concentration and effect was plotted on semilogarithmic paper. The EC10 and EC50 values were determined graphically.
Validity criteria fulfilled:
not specified
Conclusions:
The 96-h EC10 of thiourea for Scenedesmus subspicatus Chodat is in the range of 0.3-0.6 mg/L.
The 96-h EC50 of thiourea for Scenedesmus subspicatus Chodat is in the range of 4.8-10 mg/L.
Executive summary:

In a 96 hour acute toxicity study, the cultures of Scendedesmus subspicatus Chodat were exposed to thiourea at several concentrations (4 replicates per concentration, 2 parallel measurements) under static conditions in accordance with the Guideline of the German Environmental Protection Agnecy (UBA) of May 1982 (Hemmung der Zellvermehrung bei der Grünalge Scenedesmus subspicatus Chod.").


 


The EC10 and EC50 values based on cell density were 0.3 -0.6 mg/L and 4.8 -10 mg/L, respectively.


 


 


Results Synopsis:


Test Organism: Scenedesmus subspicatus Chodat


Test Type: Static


96 -hr EC10: 0.3 -0.6 mg/L


96 -hr EC50: 4.8 -10 mg/L


Endpoint effected: cell growth

Description of key information

Two publications are available that are reporting 96-hr effect concentrations for the green algae Scenedesmus subspicatus Chodat:
- Geyer et al. (1985): EC10 = 0.3 - 0.6 mg/L, EC50 = 4.8 - 10 mg/L
- Friesel et al. (1984): EC10 = 0.5 - 0.7 mg/L, EC50 = 3.8 - 5.4 mg/L
Both publications report values that are within in the same range. Due to precautionary principles, the lowest reported value for the EC10 and EC50, respectively, is used as key value in the risk assessment for thiourea.

Key value for chemical safety assessment

EC50 for freshwater algae:
3.8 mg/L
EC10 or NOEC for freshwater algae:
0.3 mg/L

Additional information

Friesel at al. (1984) and Geyer et al. (1985) both report 96 -hr EC50 and EC10 values of thiourea for the green algae Scenedesmus subspicatus Chodat. In both cases results were determined in test according to the guideline "Hemmung der Zellvermehrung bei der Grünalge Scenedesmus subspicatus Chod." of the German Environmental Protection Agency (UBA; May 1982). But as the documentation of both experiments, especially with regard to the results, is insufficient for assessment, the publications are rated as Klimisch III.


 


According to current guidelines, the standard test duration for testing of algae toxicity is 72 hours instead of 96 hours. But as the test duration in the reported experiments is longer than in standard tests, the results are considered to rather overestimate the toxicity of thiourea to algae. Thererfore, the results are deemed sufficiently precautionary to be used in the risk assessment of the substance.


 


In addition, as both publications report results that are within the same range, the results are used in a weight-of-evidence approach to assess the environmental risk of thiourea:


 


- Geyer et al. (1985): EC10 = 0.3–0.6 mg/L, EC50 = 4.8–10 mg/L


- Friesel et al. (1984): EC10 = 0.5–0.7 mg/L, EC50 = 3.8–5.4 mg/L


 


Due to precautionary principles, the lowest reported value for the EC10 and EC50, respectively, is used as key value in the risk assessment for thiourea.