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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:
2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.20 (Daphnia magna Reproduction Test)
Deviations:
no
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 211 (Daphnia magna Reproduction Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
SAMPLING SCHEDULE:
- Control: on day 0, 5 and 9 in the freshly prepared media; on day 2, 7 and 12 in the old media
- Test concentrations: .0488 mg/L and 0.1563 mg/L on day 0, 5 and 9 in the freshly prepared media; on day 2, 7 and 12 in the old media;
0.5000 mg/L on day 0 in the freshly prepared medium and on day 2 in the old medium, because of 100% immobilisation of the parent daphnids
Vehicle:
yes
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST SPECIES:
- Common name: Daphnia magna STRAUS, parthenogenic females
- Source: Strain of Bundesgesundheitsamt Berlin
- Maintenance and acclimatisation: A population of parthenogenetic females of synchronized age structure has been maintained for more than 15 years in the test facility under constant temperature conditions (20 +/- 1 °C) at a 16 : 8 hour light-dark photoperiod (light intensity:
< 20 µE x m-2 x s-1). The culture water (so-called 'M4 medium') was partly renewed once a week. The Daphnia were exclusively fed unicellular green algae (Desmodesmus subspicatus) 'ad libitum'. Mortalities of parent Daphnia during the culture period were recorded daily in a semi-quantitative way. The neonates were separated from their parent Daphnia by filtration prior to the acute test.
Test type:
semi-static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
21 d
Hardness:
14.4 °dH to 14.7 °dH (257 - 262 mg/L CaCO3)
Test temperature:
20.7-21.4 °C
pH:
8.2
Dissolved oxygen:
8.2-8.3 O2 (mg/L)
Salinity:
n.a.
Nominal and measured concentrations:
Effective concentrations ranged from 50.4 % to 76.8 % of the nominal values in the freshly prepared media and from 17.1 % to 23.6 % in the media after 48 hours, or 72 hours of exposure.
Details on test conditions:
PRE-TREATMENT OF THE TEST ITEM:
- 2 mg of the test item were added to 1 litre of dilution water and treated for 60 seconds at 8000 rpm with an ultra turrax
- To accelerate the solution procedure, 100 µL acetone were added and the solution was stirred for 2 hours on a magnetic stirrer
- The pH was measured and ranged between 8.0 and 8.2

EXPOSURE CONDITIONS:
- Test vessels: 150 mL glass beakers covered with watch glasses, holding 1 neonate in 100 mL of test medium
- Experimental design: 7 test concentrations plus 1 control; 1 neonate per vessel, 10 replicates per concentration/control
- Semi static system: (renewal of the test media on Monday, Wednesday and Friday)
- Method of initiation: neonates were placed in prepared media
- Photoperiod: 16 h light: 8 h dark
- Light intensity: not exceeding 20 µE x m-2 x s-1
- Aera: none
- Test concentration: 0.0015, 0.0048, 0.0153, 0.0364, 0.0488, 0.1563 and 0.5000 mg/L
- Food source: Desmodesmus subspicatus
- Feeding rate: : day 0-7: 0.1 mg C/Daphnia/day; day 8-21: 0.2 mg C/Daphnia/day
Reference substance (positive control):
not required
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
>= 0.057 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
reproduction
Remarks on result:
other: NOEC-statement can be misleading since in the highest treatment the experimental cohort completely died out
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
> 0.057 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
reproduction
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
0.057 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
mortality
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
0.182 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
mortality
Details on results:
The results are expressed in terms of time-weighted mean measured concentrations. Effective concentrations ranged from 50.4 % to 76.8 % of the nominal values in the freshly prepared media and from 17.1 % to 23.6 % in the media after 48 hours, or 72 hours of exposure.
Validity criteria fulfilled:
yes
Remarks:
for details see "Overall remarks"
Conclusions:
Based on different biological effects observed and endpoints assessed, the following results [mg/L] were obtained at the end of the 21-day exposure period of Daphnia reproduction test: 21d-NOEC (repr.) (tα 0.05) >= 0.057; 21d-LOEC (repr.) (tα 0.05) > 0.057; 21d-NOEC (mor.) (tα 0.05) 0.057; 21d-LOEC (mor.) (tα 0.05) 0.182.

Executive summary:

The study was conducted in accordance with Council Regulation (EC) No 440/2008, Method C.20 'Daphnia magna Reproduction Test'' (2008), which equals in all relevant parts to the OECD Test guideline 211 (Daphnia magna Reproduction Test; adopted: Oct. 03, 2008).

Young female Daphnia, aged less than 24 hours at the start of the test, were exposed to a range of concentrations, nominally 0.0015, 0.0048, 0.0153, 0.0364, 0.0488, 0.1563 and 0.5000 mg/L of Ditolylether dissolved in water. Auxiliaries used to prepare the test media were an ultra turrax and a magnetic stirrer. Acetonitrile was used as solubiliser with a concentration of 100 µL/L.

After a 21d-exposure period, the total number of living offspring produced per parent animal alive at the end of the test was assessed. The reproductive output of the Daphnia exposed to the test item was compared to that of the control in order to determine the Lowest Observed Effect Concentration (LOEC) and the No Observed Effect Concentration (NOEC) according to Williams Multiple Sequential-t Test Procedure. Additionally, the survival of the parent Daphnia and the time to production of first brood was determined.

Based on different biological effects observed and endpoints assessed, the following results [mg/L] were obtained at the end of the 21 day exposure period of the Daphnia reproduction test: 21d-NOEC (repr.) (tα 0.05) >= 0.057; 21d-LOEC (repr.) (tα 0.05) > 0.057; 21d-NOEC (mor.) (tα 0.05) 0.057; 21d-LOEC (mor.) (tα 0.05) 0.182; 1st brood on day 8.

Description of key information

The long-term toxicity of the substance to Daphnia magna was assessed in a 21-day semi-static test according to the OECD Guideline. Immobility of the parental generation and the number of offspring were assessed. The 21-day NOEC for reproduction was determined to be 0.057 mg/L. 

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Dose descriptor:
NOEC
Effect concentration:
0.057 mg/L

Additional information

ECHAconsiders in a Draft Decision on a Compliance Check that the key study is a non GLP study and has important shortcomings: the test water was not according to the current OECD 211 guideline, filtrated surface water was mixed with discharge of a sewage purification plant, no analytical monitoring was performed and results of two consecutive experiments (one using 4 and one using 3 test concentrations) were combined. However, this study was rated as invalid in a Compliance Check due to several short-comings.

Therefore, a new study on chronic exposure of daphnids with ditolyl ether was conducted. Interestingly, this study came up with a 21 days-NOEC (reproduction) of 0.057 mg/L which is nearly identical with the result of the previous study.

In conclusion, the new study confirmed the originally available data on chronic toxicity to daphnids and the new valid study fills the potential data gap for testing on chronic toxixity to daphnids.

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