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Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

See attached document in section 13 "Assessment report" for justification and rationale of the analogy approach.
Original letters from the French Competent Authorities requiring the read across to be done with cerium and iron oxide isostearate are attached below.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

22 d

Dose descriptor:

NOEC

Effect conc.:

>= 100 other: % saturated solution

Conc. based on:

test mat.

Basis for effect:

other: no toxic effects on survival and reproduction

Duration:

22 d

Dose descriptor:

LOEC

Effect conc.:

> 100 other: % saturated solution

Conc. based on:

test mat.

Basis for effect:

other: no toxic effects on survival and reproduction

Duration:

22 d

Dose descriptor:

EC50

Effect conc.:

> 100 other: % saturated solution

Conc. based on:

test mat.

Basis for effect:

other: no toxic effects on survival and reproduction

Conclusions:

Iron oxide isostearate is to be considered as cerium and iron oxide isostearate as having no toxic effects on survival and reproduction of Daphnia magna after the exposure period of 22 days up to the solubility limit of the test item in test water.

Executive summary:

The source and target substances present similar characterization (nanoparticles of very similar parameters), and similar physico-chemical and ecotoxicological properties (high melting point, low vapour pressure, very low water solubility, no expected bioaccumulation potential when considering cerium and iron elements and isostearate parts, no acute toxicity to daphnids up to and including the saturation concentration). This similarity supports the relevance of the read-across.

Thus, the long term toxicity to daphnids is expected to be the same for the source and target substances.

Iron oxide isostearate is to be considered as cerium and iron oxide isostearate as having no toxic effects on survival and reproduction of Daphnia magna after the exposure period of 22 days up to the solubility limit of the test item in test water.

Reference 2

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

from 22 July 2008 to 22 April 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations: all test concentrations and the control
- Sampling method: to determine the test item concentrations, triplicate samples were taken from the freshly prepared test media of all test concentrations and from the control at two treatment intervals in the second week (Days 7 and 12) and at a treatment interval in the last week (Day 16). To determine the maintenance of the test item concentrations in the test media, stability samples were taken at the end of two test medium renewal periods of 48 hours (Days 9 and 14) and at the end of one renewal period of 72 hours (Day 19). The following stability samples were taken in triplicate:
a) Samples with food, taken from the actual test by combining the contents of the test beakers after the end of the treatment period.
b) Samples without food and test animals, incubated during the renewal periods under the test conditions.
- Sample storage conditions before analysis: immediately after sampling, the samples were acidified with 10% (v/v) nitric acid to stabilize the samples during the storage period. Then the samples were stored at room temperature.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method:
Due to the low water solubility of the test item, a saturated solution of the test item with the loading rate of 100 mg/L was tested as the highest test concentration and was used as a stock solution for preparation of the test media of lower test concentrations (dilutions 1:10 and 1:3.2).
Prior to the start of the test and prior to each test medium renewal, a dispersion of the test item with the loading rate of 100 mg/L was prepared by dispersing 300 mg (effective weights: 299.6-301.0 mg) of the test item in 3000 mL of test water. The test item was mixed into the test water as homogeneously as possible using ultrasonic treatment for 15 minutes and intense stirring. No auxiliary solvent or emulsifier was used.
The dispersion was stirred on a magnetic stirrer at room temperature in the dark over 6 days. Thereafter, stirring was stopped and the undissolved test item was allowed to separate from the water phase (settling down on the bottom of the tank and/or swimming up to the water surface) for one day. The contact time of the test item and the test water for equilibration (i.e. stirring time and separation period) was 7 days.
After the 7 days, the equilibrated test medium (saturated solution) was carefully separated from the non-dissolved test item. Therefore the clear medium was siphoned off with a teflon tube from the middle of the water column. The saturated solution was used as the highest test concentration and was diluted with test water to obtain the lower test concentrations as stated above. The test media were freshly prepared just before the introduction of daphnids (i.e., test start) and prior to each test medium renewal.
- Controls: test water without test item

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: water flea
- Strain/clone: Straus
- Source: originally supplied by the University of Sheffield/UK in 1992 (since this date, the clone is successfully bred in Harlan Laboratories)
- Age of parental stock: < 24 hours. These daphnids originated from parental daphnids that were at least 14 days old but not older than four weeks, and were not first brood progeny
- Feeding during test
- Food type: food mixture containing a suspension of green algae of the species Scenedesmus subspicatus (freshly grown at Harlan Laboratories) and a fish food suspension.
- Amount: 0.20 mg TOC per Daphnia and day (with the exception of Day 21 when the food amount was 0.1 mg TOC per Daphnia)
- Frequency: daily

ACCLIMATION
- Acclimation period: no

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

22 d

Post exposure observation period:

none

Hardness:

2.5 mmol/L (= 250 mg/L as CaCO3)

Test temperature:

20-21°C

pH:

7.5 to 8.2

Dissolved oxygen:

8.0 to 9.4 mg/L

Nominal and measured concentrations:

Nominal loading rates: 100, 31.25 (dilution 1:3.2) and 10 mg/L (dilution 1:10)
Measured at the loading rate of 100 mg/L: 9 to 200 μg Ce/L (in the freshly prepared test medium) ; 7 to 240 μg Ce/L (at the end of the renewal periods). This results in a mean measured cerium concentration of 48 µg/L, corresponding to a test item concentration of 205 µg/L.

Details on test conditions:

TEST SYSTEM
- Test vessel: 100-mL glass beakers
- Type: closed (test vessels were covered with glass plates to reduce the loss of water by evaporation and to avoid the entry of dust into the solutions)
- fill volume: 80 mL of test medium
- Aeration: no data
- Renewal rate of test solution: the test media of all test concentrations and of the control were renewed on Days 2, 5, 7, 9, 12, 14, 16, and 19 of the test period
- No. of organisms per vessel: one
- No. of vessels per concentration (replicates): 20
- No. of vessels per control (replicates): 20
- Biomass loading rate: 80 mL of medium per parental daphnid

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: The test was conducted in a test water prepared on the basis of the Elendt M7 medium, but no EDTA was added (according to recommendation of the OECD test guideline for substances containing metals). For preparation of the test water, analytical grade salts and additives were dissolved in purified water.
- Alkalinity: 0.9 mmol/L
- Ca/Mg ratio: no data
- Culture medium different from test medium: no
- Intervals of water quality measurement: at the beginning and end of each test medium renewal period, the pH and dissolved oxygen concentrations were measured in one replicate of each test concentration and of the control. At the same time, the water temperature was measured in one of the control replicates. The appearance of the test media was visually recorded at the beginning and end of each test medium renewal period.

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: 16-hour light to 8-hour dark cycle with a 30 minute transition period
- Light intensity: 500 to 630 Lux

EFFECT PARAMETERS MEASURED:
The test replicates were observed for mortality of the parental daphnids and presence of juveniles every working day. The offspring were counted and removed three times per week at the renewal of the test media. On the same dates, the test replicates were observed for the presence of aborted eggs and dead offspring.
The reproduction rate was calculated as the total number of living offspring produced per parent female surviving until the end of the test.

RANGE-FINDING STUDY
- Test concentrations: no data
- Results used to determine the conditions for the definitive study: no data

Reference substance (positive control):

no

Key result

Duration:

22 d

Dose descriptor:

NOEC

Effect conc.:

>= 100 other: % saturated solution

Conc. based on:

test mat.

Remarks on result:

other: no toxic effects on survival and reproduction

Duration:

22 d

Dose descriptor:

LOEC

Effect conc.:

> 100 other: % saturated solution

Conc. based on:

test mat.

Remarks on result:

other: no toxic effects on survival and reproduction

Duration:

22 d

Dose descriptor:

EC50

Effect conc.:

> 100 other: % saturated solution

Conc. based on:

test mat.

Remarks on result:

other: no toxic effects on survival and reproduction

Details on results:

ANALYTICAL RESULTS:
The analytically measured concentrations of cerium in the freshly prepared test medium of the highest test concentration (saturated solution with the loading rate of 100 mg/L) ranged from 9 to 200 μg/L. At the end of the renewal periods, concentrations of cerium between 7 and 240 μg/L were measured. Three samples presented relatively high cerium concentrations. It can be assumed that this was caused by suction of not sedimented test item. Finally, there was no significant difference between the concentration measured in samples taken from the actual test at the end of the renewal periods and the concentration measured in samples which were incubated under the test conditions without food and daphnids in parallel to the test. The mean measured concentration of cerium was 48 μg/L, corresponding to a test item concentration of 205 μg/L (based on a cerium content of 23.4%). 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 at all test concentrations, the survival of the test animals at the end of the test was 95%. Thus, the survival of Daphnia magna over 22 days was not affected by the test item up to the water solubility limit of the test item.
The first young offspring released from their parent animals were recorded in the control and at all test concentrations at observation on Day 7. Thus, the time of the first brood was not affected by the test item up to the water solubility limit of the test item.
The mean reproduction rate of the daphnids in the control was 125.3 ± 14.7 living offspring per surviving adult. No significant inhibitory effect of the test item on the mean reproduction rate was determined up to and including the loading rate of 100 mg/L and thus, up to the water solubility limit of the test item (Williams’ test, one-sided, α = 0.05).
No visible abnormalities were observed in the test animals during the test.

Results with reference substance (positive control):

No reference substance used.

Reported statistics and error estimates:

None as no adverse effect was observed.

Table 1: Number of Surviving Test Animals

Exposure day	Treatment / dilution
	control	Dilution 1:10	Dilution 1:3.2	Saturated solution (loading rate 100 mg/L)
0 1 2 5 6 7 8 9 12 13 14 15 16 19 20 21 22 20 21 22	20 20 20 20 20 20 20 20 20 20 20 20 20 20 19 19 19 19 19 19	20 20 20 20 20 20 20 20 20 20 20 19 19 19 19 19 19 19 19 19	20 20 20 20 20 20 20 20 20 19 19 19 19 19 19 19 19 19 19 19	20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 19

Table 2: Number of Living Offspring Produced per Surviving Adult after 22 Days of Exposure

	Treatment / dilution
Replicate N°	control	Dilution 1:10	Dilution 1:3.2	Saturated solution (loading rate 100 mg/L)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20	137 110 101 144 107 134 93 137 123 123 130 116 128 136 113 132 139 138 140 *	125 162 70 136 127 * 118 137 122 124 120 125 111 120 100 118 121 109 113 139	118 110 109 120 98 118 136 145 137 141 120 119 104 132 113 127 117 * 104 178	128 116 123 * 111 111 133 125 117 148 124 108 114 122 111 114 131 134 106 161
Mean SD N	125.3 14.7 19	120.9 18.2 19	123.5 18.6 19	123.0 14.1 19
CV %	11.8	15.0	15.1	11.5
% of control	100	96.5	98.5	98.2
STAT	-	n.s.	n.s.	n.s.

*: test animal died during the test period

SD: standard deviation

CV %: coefficient of variation: (SD/mean)⋅100%

STAT: results of a Williams’ test (one-sided,α= 0.05) with the mean values of living offspring

Validity criteria fulfilled:

yes

Remarks:

Mortality of the parent animals at the end of the test < 20%, Mean number of live offspring produced per parent animal surviving at the end of the test > 60%, acceptable pH, T° and oxygen concentration.

Conclusions:

The test item had no toxic effects on survival and reproduction of Daphnia magna after the exposure period of 22 days up to the solubility limit of the test item in test water. Thus, the 22-day NOEC of the test item was determined to be >= 100% saturated solution.

Executive summary:

The effect of the test item cerium and iron oxide isostearate on the survival and reproduction of Daphnia magna was investigated in a semi-static test over 22 days following the OECD Guideline No. 211 and under GLP-compliance. Daphnids were exposed to control and test chemical at nominal loading rates of 10 (dilution 1/10), 31.25 (dilution 1/3.2) and 100 mg/L (saturated solution, mean measured concentration 205 µg/L). The mortality and reproduction of the exposed daphnids were compared with the corresponding parameters in the control.

The test item cerium and iron oxide isostearate had no toxic effects on survival and reproduction of Daphnia magna after the exposure period of 22 days up to the solubility limit of the test item in test water. Thus, the 22-day NOEC of the test item was determined to be >= 100% saturated solution.

Description of key information

By analogy with cerium and iron oxide isostearate (active matter of DPX10), iron oxide isostearate (active matter of DPX13) should not have any adverse chronic effect on survival and reproduction of daphnids.

Additional information

One GLP-compliant study performed according to OECD guideline 211 is available on the analogue, cerium and iron oxide isostearate (active matter of DPX10). It is quoted as reliability 1 according to Klimisch criteria and flagged as a key study.