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Long-term toxicity to aquatic invertebrates

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Reference
Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2015
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 211 (Daphnia magna Reproduction Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Details on sampling:
Samples for analysis were taken from all test concentrations and the control on 4 occasions throughout the test, on fresh and old solutions:

- at days 1 (fresh solutions) and 2 (old solutions)
- at days 8 (fresh solutions) and 9 (old solutions)
- at days 13 (fresh solutions) and 14 (old solutions)
- at days 20 (fresh solutions) and 21 (old solutions)

Concentrations were measured immediately.
Vehicle:
no
Details on test solutions:
Tests solutions were prepared from dilutions of a stock solution: a known volume of test item was poured into a volumetric flask, the volume was then made up to the required volume with test medium. The solution was kept under high speed stirring at ambient temperature during approximately 15 minutes with a magnetic stir bar. The study was conducted under semi-static conditions (meaning that all test solutions were renewed daily, including saturdays and sundays). A test item stock solution was thus prepared daily before test solutions renewal.
Test organisms (species):
Daphnia magna
Details on test organisms:
The test organisms used for this study was Daphnia magna Straus (Cladocera, Crustacea), clone 5, bred within the laboratory by acyclical parthenogenesis in a synthetic medium. The neonates used were less than 24h old at test initiation (selected by sieving) and were not first brood progeny. Test animals were fed a diet of 0.1 - 0.2 mg of carbon per daphnid per day, in the form of a suspension of the algal strains Chlorella vulgaris (25%) and Pseudokirchneriella subcapitata (75%), except during the initial three days of culture when a slightly lower ration was given.
Test type:
semi-static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
21 d
Remarks on exposure duration:
None.
Post exposure observation period:
None.
Hardness:
170 mg/L as CaCO3.
Test temperature:
18.3 - 20.1 °C (min-mix)
pH:
7.3 - 8.3
Dissolved oxygen:
8.4 - 9.9 mg/L
Salinity:
freshwater
Conductivity:
Not applicable.
Nominal and measured concentrations:
Nominal: 0 ; 0.05 ; 0.15 ; 0.49 ; 1.5 ; 5 mg/L
Measured: 0 ; 0.046 ; 0.148 ; 0.48 ; 1.49 ; 4.9 mg/L (arithmetic mean based on 4 new/old measurements).

Since measured concentrations were within [80 - 120] % of the nominal concentrations, results were based on nominal concentrations.
Details on test conditions:
TEST SYSTEM
- Test vessel: tubes
- Material, size, headspace, fill volume: clear glass tubes (120 mL capacity), stoppered with cellulose bungs to minimise evaporation and dust.
- Aeration: None
- Semi-static: daily renewal, including weekends
- No. of organisms per vessel: 1
- No. of vessels per concentration (replicates): 10
- No. of vessels per control (replicates): 10

OTHER TEST CONDITIONS
- Adjustment of pH: None
- Photoperiod: 16L:8D
- Light intensity: 3450 lumen

EFFECT PARAMETERS MEASURED
- Number of dead parents per day
- Number of living neonates par day
- Age at first brood
Reference substance (positive control):
no
Key result
Duration:
21 d
Dose descriptor:
EC10
Effect conc.:
1.67 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
reproduction
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
> 5 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
mortality
Remarks:
Parental mortality
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
> 5 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
other: Age at first brood
Details on results:
All test solutions appeared clear and colourless. No precipitation of test item nor undissolved particles were observed. Chemical analysis of test samples confirmed the stability of the substance over 24-hour exposure. Test item concentrations remained between 80% and 120% of the nominal concentrations in each treatment group for each sampling time. Based on these results, the exposure concentrations used for statistical analysis were based on the nominal concentrations.

The number of immobile adult Daphnia magna recorded during the reproduction test was 1 (10%) at 0.05 mg/L and 1 (10%) at 5.0 mg/L of test item. There were no immobile Daphnia magna in the control group and in the 0.15, 0.49 and 1.50 mg/L groups.

The numbers of offspring produced for each concentration (0 ; 0.05 ; 0.15 ; 0.49 ; 1.56 ; 5 mg/L) during the test were respectively 103, 106, 104, 106, 96 and 19 living neonates per living parent at the test of the test (Table 1).
Results with reference substance (positive control):
None.
Reported statistics and error estimates:
Nominal concentrations of test item in the test solutions were used in the estimation of ECx and NOEC/LOEC values. Analysed variables were number of living neonates produced per living parent at the end of the test, parent immobilisation and mean time to first brood. All statistical analysis were conducted using the Software ToxRat 2.10.

Concentrations (mg/L)

Control

0.05

0.15

0.49

1.56

5

Mean number of neonates

103

106

104

106

96

19

Parent immobilization (%)

0

10

0

0

0

10

Table 1: parent immobilization and mean number of living neonate produced per surviving parents at the end of the test for each concentration tested (expressed as geometric means).

Validity criteria fulfilled:
yes
Conclusions:
The toxicity of 1,3-diethyl-2-thiourea was tested on Daphnia magna reproduction according to the OECD 211 guideline. The lowest NOEC/EC10 (neonate production) was 1.67 mg/L. There were no effects of 1,3-diethyl-2-thiourea on parent survival and age at first brood.
Executive summary:

This study was designed to determine the effects of 1,3 -diethyl-2 -thiourea on Daphnia magna reproduction and survival in a 21 days test according to the OECD 211 Guideline. The total test period was 21 days; all test solutions (including control) were renewed every day (including "weekend" periods). Ten replicate test vessels were prepared for the control and the test concentration. A single juvenile Daphnia magna (<24 hours old selected by sieving) was added to each test vessel. Each day, parental animals were transferred into freshly prepared test media. Dead parents were noted and discarded. All produced juveniles were counted every day. Chemical analysis of test samples confirmed the stability of the substance over a 24-hour test period. Based on these results, the exposure concentrations were based on the nominal concentration. EC10 and NOEC values on day 21 were determined as follows:

EC10 for mean number of neonate produced per parent alive at the end of the test: 1.67 mg/L

NOEC for parent mobility: > 5 mg/L

NOEC for age at first reproduction: > 5 mg/L.

Description of key information

This study was designed to determine the effects of 1,3 -diethyl-2 -thiourea on Daphnia magna reproduction and survival in a 21 days test according to the OECD 211 Guideline. The total test period was 21 days; all test solutions (including control) were renewed every day (including "weekend" periods). Ten replicate test vessels were prepared for the control and the test concentrations. A single juvenile Daphnia magna (<24 hours old selected by sieving) was added to each test vessel. Each day, parental animals were transferred into freshly prepared test media. Dead parents were noted and discarded. All produced juveniles were counted every day. Chemical analysis of test samples confirmed the stability of the substance over a 24-hour test period. Based on these results, the exposure concentrations were based on the nominal concentration. The lowest EC10/NOEC value on day 21 (neonate production) was 1.67 mg/L.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
1.67 mg/L

Additional information