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Short-term toxicity to fish

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Endpoint:
short-term toxicity to fish
Type of information:
experimental study
Adequacy of study:
key study
Study period:
6-8 June 1988
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods
Remarks:
GLP Guideline study (German DIN 38412). Purity of the test substance is not reported. But as neither lethal nor sublethal effects could be observed at very high concentrations up to 10 g/L, impurities (if present) did not have a negative effect on the overall outcome of the test.
Qualifier:
according to guideline
Guideline:
other: DIN 38412
GLP compliance:
yes
Analytical monitoring:
no
Details on sampling:
Not applicable.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: 10, 18, 32, 56, and 100 g thiourea were accurately weighed out and dissolved in water (10 L).


COMPOSITION OF SYNTHETIC DILUTION WATER ACCORDING TO DEV L15:
- Concentrated solutions:
1) CaCl2 * 2 H2O: 73.54 g/L
2) MgSO4 * 7 H2O:123.25 g/L
3) NaHCO: 38.401 g/L
- Synthetic dilution water:
44 ml of the concentrated solution no. 1, 10 mL of no. 2, and 64 mL of no. 3 are diluted with distilled water to 10 L. This solution is aerated until a constant pH is reached.
Test organisms (species):
Leuciscus idus
Details on test organisms:
TEST ORGANISM
- Common name: Ide ("Goldorfe")
- Source: commercial hatchery P. Eggers (Martensweg 18, Postfach 56, 2354 Hohenwestedt, Germany)
- Average length at study initiation: 5.2 +/- 0.3 cm
- Average weight at study initiation: 1.2 +/- 0.2 g
- Average "Korpulenzfaktor" at study initiation: 0.9 +/- 0.08 g/cm³
- Feeding during test: none

ACCLIMATION
- Acclimation period: 11 days
- Acclimation conditions: same
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Post exposure observation period:
None
Hardness:
No data.
Test temperature:
20 +/- 1 °C
pH:
7.0 - 7.7
Dissolved oxygen:
> 5.9 mg/L
Salinity:
Not applicable.
Nominal and measured concentrations:
Nominal: 1, 1.8, 3.2, 5.6, and 10 g/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 12 L all-glass aquaria
- Material, fill volume: glass, 10 L
- Aeration: slightly
- No. of organisms per vessel: 10
- No. of vessels per concentration: 1
- No. of vessels per blank control: 1

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: 12:12 h

EFFECT PARAMETERS MEASURED: mortality and swimming behaviour at Hours 0, 24, and 48

TEST CONCENTRATIONS
- Range finding study: yes; appropriate concentrations for the toxicity test were determined in a preliminary range-finding test, carried out however, with Brachydanio rerio
- Test concentrations: five
Reference substance (positive control):
no
Key result
Duration:
48 h
Dose descriptor:
LC50
Effect conc.:
> 10 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mortality (fish)
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
>= 10 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: swimming behaviour
Details on results:
No further results reported.
Results with reference substance (positive control):
Not applicable.
Reported statistics and error estimates:
The slope of the concentration-effect curve could not be calculated.
Sublethal observations / clinical signs:

Table 1: Numbers of surviving fish and their condition at several concentrations of thiourea and after several exposure times

Time [h]

Concentration of test substance [mg/L]

0

1,000

1,800

3,200

5,600

10,000

0

10

10

10

10

10

10

24

10

10

10

10

10

10

48

101)

102)

102)

102)

102)

102)

1) Condition of all fish, visually assessed, normal (= good)

2) Condition of all fish, visually assessed, equal to that of the control fish

Validity criteria fulfilled:
yes
Conclusions:
The 24 h and 48 h LC50 values of thiourea for Leuciscus idus (L.) were found to be greater than 10,000 mg/L.
Executive summary:

The acute toxicity of thiourea to the freshwater fish species Leuciscus idus (L.) ("Goldorfe") was determined as laid down in DIN 38412 "Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung" (DEV-11. Lieferung 1982) L15.

The 24h and 48h LC50 were found to be greater than 10,000 mg/L.

At 10,000 mg/L all animals were living after 48 h exposure.

The slope of the concentration-effect curve could not be calculated.

After 48h exposure at 10,000 mg/L, the number of living animals and their condition, visually assessed, were the same as those of the control animals.

The solubility of thiourea in water was 136 g/L according to the sponsor.

Endpoint:
short-term toxicity to fish
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1981
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Qualifier:
no guideline followed
Principles of method if other than guideline:
Groups of five fish (Pimephales promelas) per concentration (2 replicates) were exposed to thiourea in at least 5 concentrations (spacing factor: 0.6) and one control with dilution water only in 12 L bioassay containers for 96-hr under static conditions. The maximum concentration of thiourea was 600 mg/L.
During the test deaths were recorded and bodies were removed whenever noticed. After 24 hr, the number of surviving fish, temperature , and dissolved oxygen were determined. At the end of the test the pH and actual test substance concentration were measured. The actual test substance concentration was also measured at the beginning of the test.
At the end of the test control organisms were weighed and measured to evaluate the average seize of the fish.
96-hr LC50 values were calculated by plotting concentration vs. mortality results.
GLP compliance:
not specified
Analytical monitoring:
yes
Details on sampling:
- Sampling method: water sample was removed form test vessels (no details reported)
- Sample storage conditions before analysis: no data
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: toxicants were either added directly or in stock solution (deionized water)
Test organisms (species):
Pimephales promelas
Details on test organisms:
TEST ORGANISM
- Common name: Fathead minnow
- Source: E.P.A. Newton Fish Toxicology Station, Cincinnati, Ohio
- Fish were observed at least 14 days before they were used in the definitive test

ACCLIMATION
- Acclimation period: 4 days
- Acclimation conditions: same as test (22 °C, 100 % dilution water) for at least 2 days; batches with more than 3 % mortality during this period were not used in the test

Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
96 h
Hardness:
40 - 48 mg/L CaCO3
Test temperature:
22 +/-1 °C
pH:
7.2-7.9
Dissolved oxygen:
not specified
Salinity:
not applicable
Conductivity:
not specified
Nominal and measured concentrations:
not specified
Details on test conditions:
TEST SYSTEM
- Test vessel: bioassay containers
- Type: open
- Material, size, headspace, fill volume: 12 L (water depth ~24 cm)
- No. of organisms per vessel: 5
- No. of vessels per concentration: 2
- No. of vessels per control: 2
- Biomass loading rate:

TEST MEDIUM / WATER PARAMETERS
- Alkalinity: 30-35 mg/L CaCO3
- Conductivity: 120-160 µS/cm


TEST CONCENTRATIONS
- Spacing factor for test concentrations: 0.6
- Test concentrations: at least five
Reference substance (positive control):
no
Key result
Duration:
96 h
Dose descriptor:
LC0
Effect conc.:
<= 600 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
mortality (fish)
Remarks on result:
other: not applicable
Details on results:
No further fetails reported.
Results with reference substance (positive control):
Not applicable.
Reported statistics and error estimates:
96-hr LC50 values and 95 % confidence limits were calculated by means of the probit analysis or the moving average calculations for data showing two or more partial kills. The binomial test method was used for data having less than two partial kills.
Sublethal observations / clinical signs:

- Mortality in the controls was below 10 %.

Validity criteria fulfilled:
yes
Remarks:
Mortality in the control group was below 10 %.
Conclusions:
The 96-hr LC0 of thiourea for Pimephales promelas is
Executive summary:

In a 96-h acute toxicity study, the freshwater fish Pimephales promelas (fathead minnow) was exposed to thiourea at to at least five concentrations (spacing factor 0.6; maximum concentration: 600 mg/L; control: 0 mg/L) under static conditions.


 


The 96-h LC0 was determined to be </= 600 mg/L as no mortality occurred at the concentrations tested.


 


Based on the results of this study, thiourea would be classified as non-toxic to Pimephales promelas under the conditions of this test.


This toxicity study is classified as acceptable and satisfies the requirement for a short-term toxicity study to fish.


 


Results Synopsis:


Test organism: Pimephales promelas


Test Type: Static, 96 -hr


LC50: > 600 mg/L


LC0 </= 600 mg/L


Endpoint Effected: mortality

Description of key information

Five different studies were available in the assessment of the acute toxicity of thiourea towards fish. Species tested were Pimephales promelas, Leuciscus idus (L.), Hong Kong Guppy, Danio rerio and Oryzias latipes. In none of the studies a LC50 value could be obtained that would be close to the regulatory cut-off value of 100 mg/L for classification. Therefore, a classification of thiourea for acute toxicity to fish is not warranted.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish
Dose descriptor:
LC50
Effect concentration:
10 000 mg/L

Additional information

Five different studies are available for the assessment of the acute fish toxicity of thiourea. Two of these studies were rated reliable with a reliability code of Klimisch I (TNO, 1988) and Klimisch II (Curtis & Ward, 1988), and were therefore used as key studies in the chemical safety assessment. The remaining studies were rated unreliable and are used as supporting information in the assessment. Some information was not further included in the assessment due to considerable doubt on the correctness of reported results (“disregarded studies”).


 


In a 96-h acute toxicity study, Curtis & Ward (1981) determined the toxicity of thiourea to the freshwater fish Pimephales promelas (fathead minnow) at five concentrations (spacing factor 0.6; maximum concentration: 600 mg/L; control: 0 mg/L) under static conditions. The 96-h LC0 was determined to be ≤ 600 mg/L as no mortality occurred at any of the concentrations tested.


 


In 1988, TNO conducted a acute toxicity study for thiourea with the freshwater fish species Leuciscus idus (L.) ("Goldorfe") according to DIN 38412 "Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung" (DEV-11. Lieferung 1982) L15. The total exposure duration was 48 h. After 48 h, no mortality or other signs of sublethal effects could be observed at 10,000 mg/L which was the highest concentration tested. The 48h LC50 value was found to be greater than 10,000 mg/L.


Although the test duration of 48 h used in this study conducted by TNO (1988) is shorter than the recommended standard test duration of 96 h, this information is used in the chemical safety assessment as the study is considered reliable and the highest concentration tested – at which at the same time no lethal or sublethal effects could be observed - is a factor of 100 higher than the regulatory cut-off value of 100 mg/L for classification.


 


The results from the two key studies (Curtis & Ward, 1981; TNO, 1988) clearly demonstrate that thiourea cannot be classified as toxic towards fish. This information is further supported by the following information:


 


In 1977, experiments on the acute toxicity of thiourea to fish were conducted at the SKW Trostberg laboratory using Hong Kong Guppy (guideline or method not reported; Klimisch III). At 6,000 mg/L Hong Kong Guppies showed 100% mortality after 14 h of exposure, no animals died at 5,000 mg/L, however the total exposure duration was not reported for this dose level.


 


In 1981, Danio rerio fish were exposed to thiourea in a study conducted by Korte & Greim under static through conditions for a 48-h. The 48-h LC50 was found to be 16,000mg/L, (LC50 = 16,000 mg/L, LC100 = 20,000 mg/L).


 


The following information is available for thiourea but is not further considered in the chemical safety assessment (disregarded studies”):


 


The BUA Stoffbericht 179 (1996) cites results on the acute toxicity (48 h) of thiourea for Oryzias latipes from "Japan Chemical Industry Ecology - Toxicology and Information Center. 1992. Biodegradation and Bioaccumulation Data of Existing Chemicals Based on the CSCL Japan". The 48-h LC50 toxicity of thiourea for Oryzias latipes is cited to be below 1000 mg/L. This result is considerably lower than the other reported LC50. This could be attributed to a specific species sensitivity of Oryzias latipes. However, there is doubt that this result is cited correctly in the BUA Stoffbericht 179, because also the result of Korte & Greim (1981) for the 48-h LC100 for Danio rerio was falsely cited as being below 20,000 mg/L. Unfortunately, the original reference for Oryzias latipes was not available for review.


 


In 1977, the SKW Trostberg laboratory also conducted experiments on the acute toxicity of thiourea to fish were conducted at using Leuciscus idus (guideline or method not reported; Klimisch III). 100 % mortality was found for Leuciscus idus after 8 h and 2 h exposure at 5,000 mg/L and 6,000 mg/L, respectively. No animals died at 4,000 mg/L (however, total exposure duration not reported for this dose level). This result for Leuciscus idus is in conflict with the results from the TNO study (1988) which was rated to be reliable (Klimisch I). Therefore, the result of SKW Trostberg (1977) is not further considered in the chemical safety assessment.