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Short-term toxicity to aquatic invertebrates

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Reference
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From 5 August 2005 to 6 December 2005
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 100 mg/L (loading rate)
- Sampling method: duplicate samples were taken from the test and control medium, just before the start of the test and after 48 hours (stability samples, incubated without daphnids)
- Sample storage conditions before analysis: all samples were deep-frozen (ca. -20°C) immediately after sampling.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION:
Method: Due to low water solubility of the test item a supersaturated dispersion with a loading rate of 100 mg/L was prepared by weighing 303.2 mg of the test item into 3000 mL of test water. No auxiliary solvent or emulsifier was used. The test item was mixed into the test water as homogeneously as possible using ultrasonic treatment for 15 minutes and intense stirring for 7 days at room temperature in the dark. The long stirring period of 7 days was chosen to dissolve a maximum concentration of the test item in the dispersion.
Then, the dispersion of the test item was filtered through a membrane filter (Schleicher & Schuell, type NC45, pore size 0.45 µm). The undiluted filtrate of the dispersion with maximum concentration of dissolved test item was used as the single test medium. The test meddium was prepared just before introduction of daphnids.
- Differential loading: No (limit test)
- Control: yes, test water without test item.
- Evidence of undissolved material: The test medium was a clear solution throughout the whole test duration.
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM
- Common name: water flea
- Strain: Daphnia magna Straus clone 5
- Source: originally supplied by the University of Sheffield/UK in 1992
- Age at study initiation: 6-24 hours old, not first brood progeny
- Method of breeding: in the laboratories of RCC in reconstituted water of the quality identical to the water quality used in the test.
- Feeding during test: no
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
48 h
Post exposure observation period:
none
Hardness:
250 mg/L as CaCO3
Test temperature:
20-21°C
pH:
Control: 7.9-8.0
Undiluted filtrate: 7.5-7.9
Dissolved oxygen:
Control: 8.5-8.8 mg/L
Undiluted filtrate: 7.8-8.6 mg/L
Salinity:
not applicable
Nominal and measured concentrations:
Nominal loading rates: 0 and 100 mg/L
Measured concentrations: < LOQ (0.002 mg Fe3+/L)
Details on test conditions:
TEST SYSTEM
- Test vessel: 100 mL glass beakers
- Type: closed (covered with glass plates)
- Fill volume: 50 mL
- Aeration: prior to the start of the test, but not during the test
- No. of organisms per vessel: 5
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 4
- Biomass loading rate: less than one Daphnia per 5 mL of test solution.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Reconstituted test water:
CaCl2 x 2 H2O: 2.0 mmol/L (= 294 mg/L)
MgSO4 x 7 H2O: 0.5 mmol/L (= 123mg/L)
NaHCO3: 0.75 mmol/L (= 65 mg/L)
KCl: 0.075 mmol (= 5.8 mg/L)
Alkalinity: 0.8 mmol
Ratio Ca:Mg = 4:1 (based on molarity)
Ratio Na:K = 10:1 (based on molarity)
- Culture medium different from test medium: No
- Intervals of water quality measurement: At the start and at the end of the test, the pH values, the dissolved oxygen concentrations and the water temperature were measured in the single test concentration and the control. The appearance of the test medium was recorded at the start of the test and then daily.

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: 16-h light, 8-h dark
- Light intensity: 570-740 lux

EFFECT PARAMETERS MEASURED: immobility after 24 and 48h

TEST CONCENTRATIONS
- Spacing factor for test concentrations: not relevant (limit test)
- Range-finding study: yes
- Test concentration of the range finding study: no data.
- Results used to determine the conditions of the definitive study: no mortality at the undiluted loading rate.
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
>= 100 other: % saturated solution
Conc. based on:
test mat.
Basis for effect:
mobility
Key result
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 100 other: % saturated solution
Conc. based on:
test mat.
Basis for effect:
mobility
Details on results:
ANALYTICAL RESULTS: The analytically measured test item concentration in the analysed test item samples (the undiluted filtrate of the supersaturated dispersion) was below the limit of quantification at the start and the end of the test. The solubility limit into water reached during this test was thus different from that obtained during the water solubility test (see IUCLID section 4.8). Such contrasting results could be explained by the different water media used in the water solubility test and ecotoxicological studies (media containing analytical grade salts).

BIOLOGICAL RESULTS: In the control and in the undiluted filtrate of the loading rate of 100 mg/L corresponding to a saturated solution, no immobilised test organisms were observed during the test period of 48 hours. No remarkable observations were made concerning the appearance of the test medium.
Results with reference substance (positive control):
The latest result of the positive control test in february 2005 (25-h EC50: 1.3 mg/L) showed that the toxic performance was valid and within the range given in the OECD guideline.
Reported statistics and error estimates:
not applicable
Validity criteria fulfilled:
yes
Conclusions:
Iron oxide isostearate had no acute toxic effects on Daphnia magna up to its solubility limit in the test water at the loading rate of 100 mg/L under the present test conditions.
Executive summary:

The 48hr-acute toxicity of iron oxide isostearate to Daphnia magna was studied under static conditions according the OECD Guideline N°202 and under GLP-compliance. Daphnids were exposed to control and test chemical at a nominal loading rate of 100 mg /L for 48 hr.The water-soluble fraction (WSF) procedure was applied to prepare the test solutions. Mortality/immobilization was observed daily.

In the control and at the loading rate of 100 mg/L no immobilized test organisms were determined during the test period of 48 h. Thus, the 48 hour EC50 is > 100 % saturated solution and the 48 hour NOEC is ≥ 100 % saturated solution. As no adverse effect was observed at the highest loading rate tested (i.e. 100 mg/L), which corresponded to the maximum concentration of dissolved test item, iron oxide isostearate is not acutely toxic for daphnids up to its solubility limit into water.

Description of key information

The 48-hour EC50 of iron oxide isostearate was > 100% saturated solution. Hence, iron oxide isostearate is not acutely harmful for the daphnids up to and including its water solubility limit.

Key value for chemical safety assessment

Additional information

One GLP-compliant study performed according to OECD guideline 202 is available on iron oxide isostearate (active matter of DPX13). It is quoted as reliability 1 according to Klimisch criteria and flagged as a key study.