Cerium dioxide

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

This study, fully described with respect to the experimental conditions and the results, is not used to make an analogy with cerium oxide. It is used in parallel of the study of Yang et al. (1999) to bring evidence that insoluble and soluble forms of a same rare earth behave similarly in terms of bioaccumulation potential.

Qualifier:

no guideline followed

Principles of method if other than guideline:

During this study, only an uptake phase was carried out.

GLP compliance:

no

Radiolabelling:

no

Details on sampling:

- Sampling intervals/frequency for test organisms: Based on the table of results presented in the publication, fish were sampled after 5, 10, 17, 24, 31, 38 and 45 days of exposure.

- Sampling intervals/frequency for test medium samples: No data.

- Sample storage conditions before analysis: No data.

- Details on sampling and analysis of test organisms and test media samples (e.g. sample preparation, analytical methods): After being sacrificed, the sampled fish were rinsed with distilled water and the surface of the fish bodies were dried. Dissection was made to divide the fish into various tissue categories: skeleton, muscles, gills, internal organs, which were removed into respective 25-mL tall-form beakers. These samples were digested with HNO3-HClO4 mixture and evaporated to near dryness. The residue were dissolved in 80 mL of 0.8 mol/L HCl and transferred to 8 x 200 mm columns packed with 1 x 8 strong cation exchangers (Dowex 50-X8). K, Na, Li, Bi, Mo, W, Cd, Pt, Au and Hg in the solutions were not adsorbed by the resins and washed away with the solutions. Then 90 mL of 1.75 mol/L HNO3 was added to each column to elute Ba and Sr, folloed by 70 mL of 1.2 mol/L HCl to elute Fe, Al, Ca, Mg, Mn and Ti. These previous procedures allowed to separate the rare earth elements from the major element matrices. If not, analytical difficulties may arise due to the low contents and bad distributions of the rare earth elements in the organisms as compared with major elements as Ca, Mg, Na and K. The rare earth elements adsorbed on the resins were finally eluted by 140 mL of 4 mol/L HCl. The eluates were evaporated to about 1 mL, transferred to 10-mL volumetric flasks, and made up to volume with distilled water. The resultant solutions were subsequently used for analysis by ICP-AES.

- Sampling of fish food: Some of the dry fish food was dissolved in HNO3 and its rare earth elements contents were determined by ICP-AES.

Vehicle:

no

Details on preparation of test solutions, spiked fish food or sediment:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The La, Gd, and Y stock solutions were added dropwise to the diluent water with stirring either separately in the group A, B, C, respectively, or in interaction in the group D.
- Controls: Two additional aquaria were tested in parallel.
- Evidence of undissolved material (e.g. precipitate, surface film, etc): No data.

Test organisms (species):

Cyprinus carpio

Details on test organisms:

TEST ORGANISM
- Common name: carp.
- Age at study initiation: first-year juveniles.
- Length at study initiation: 5.5 to 7.3 cm (average = 6.4 cm).
- Weight at study initiation: 4.2 to 8.7 g (average = 6.2 g).
- Feeding during test: Fish were fed on dry food every other day one hour prior to each renewal.
No further data.

ACCLIMATION
- Acclimation period: 10 days.
- Acclimation conditions: same as test.
- Health during acclimation: The mortality rate was less than 5 %.
No further data.

Route of exposure:

aqueous

Test type:

semi-static

Water / sediment media type:

natural water: freshwater

Total exposure / uptake duration:

45 d

Total depuration duration:

0 d

Hardness:

53 - 60 mg/L as CaO

Test temperature:

11 - 14 °C

pH:

Water pH was modified to 6 intermittently with HNO3 in order to minimize possible precipitation ion exchange and adsorption of the rare earth elements.

Dissolved oxygen:

> 7 mg/L

TOC:

No data

Salinity:

Not applicable

Details on test conditions:

TEST SYSTEM
- Test vessel:
* Type (open / closed): No data
* Material, size, headspace, fill volume: Glass aquaria with a 20-L capacity filled with 15 L of the diluent water.
- Aeration: The test water was well aerated.
- Type of flow-through: not a flow-through, but a semi-static test.
- Renewal rate of test solution (frequency/flow rate): A volume of 10 L of test solution in each aquarium was renewed every other day.
- No. of organisms per vessel: 20 fish in the groups A,B,C,D exposed to rare earth elements, 10 fish in control groups.
- No. of vessels per concentration (replicates): 2.
- No. of vessels per control replicates): 2.
- Biomass loading rate: 8.27 g/L in the groups A,B,C,D. 4.13 g/L in the control groups supposing that the water volume was the same as in the exposed groups.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Tap water purified and dechlorinated through a water purifier mainly consisting of filter papers and activated carbon.
- Particulate matter: No data.
- Metals, Pesticides: No data.
- Chlorine: 7 - 8.5 mg/L.
- Alkalinity: No data.
- Ca/mg ratio: No data.
- Conductance: 170 mOhms/cm
- Holding medium different from test medium: The same water was used as the diluent employed in all testing.
- Intervals of water quality measurement: No data.
- Intervals of test medium replacement: A volume of 10 L of test solution in each aquarium was renewed every other day.

OTHER TEST CONDITIONS
- Adjustment of pH: Water pH was modified to 6 intermittently with HNO3 in order to minimize possible precipitation ion exchange and adsorption of the rare earth elements.
- Photoperiod: No data
- Light intensity: No data.

RANGE-FINDING / PRELIMINARY STUDY
No data.

Nominal and measured concentrations:

Groups A, B, C: The three rare earths are tested separately with a final concentration of 0.5 mg/L.
Group D: The three rare earths are tested in interaction and the mixed solution contained a final concentration of 0.5 mg/L of each element.

Reference substance (positive control):

no

Details on estimation of bioconcentration:

BASIS INFORMATION
- Measured/calculated logPow: Not applicable to inorganic substances.
No further data.

BASIS FOR CALCULATION OF BCF
The maximum BCF was calculated by dividing the maximum concentration of a rare earth element in certain tissue of carp by the nominated concentration of the same element in the test water.

Type:

BCF

Value:

>= 3.2 - <= 91 dimensionless

Time of plateau:

45 d

Calculation basis:

other: At the end of the 45 days, the equilibrium was reached or approached

Remarks on result:

other: Muscles: BCF = 3.2, Skeleton: BCF = 6.1, Gill: BCF = 18, Internal organs: BCF = 91

Remarks:

Conc.in environment / dose:[La] = 0.5 mg/L

Type:

BCF

Value:

>= 3.5 - <= 105 dimensionless

Time of plateau:

45 d

Calculation basis:

other: after 45 days, the equilibrium was reached or approached

Remarks on result:

other: Muscles: BCF = 3.5, Skeleton: BCF = 5, Gill: BCF = 14, Internal organs: BCF = 105

Remarks:

Conc.in environment / dose:[Gd] = 0.5 mg/L

Type:

BCF

Value:

>= 1.3 - <= 54 dimensionless

Time of plateau:

45 d

Calculation basis:

other: After 45 days, the equilibrium was reached or approached

Remarks on result:

other: Muscles: BCF = 1.3, Skeleton: BCF = 3.8, Gill: BCF = 8, Internal organs: BCF = 54

Remarks:

Conc.in environment / dose:[Y] = 0.5 mg/L

Details on results:

There was no mortality of fish during the 45-day exposure period.

Rare earth concentration in fish food:

Contents of the rare earth elements in the dry fish food were all under the detection limits. This result gave the assurance that the bioaccumulation process was not partly due to food-derived rare earth elements.

Bioaccumulation in carp:

The bioaccumulation values (differences between the background concentration in unspiked fish tissue and the concentration in spiked tissue) in various tissues of carp, both in individual and mixed rare earth groups, increased with time. At the end of the 45 -day exposure period, the equilibrium was reached or approached. The pattern of accumulation for all the elements were similar, suggesting that carp accumulated the three rare earths at a comparable rate. The bioaccumulation values for individual element solutions (Groups A,B,C) and those for mixed rare earth solution (Group D) were in good agreement, with no significant difference; indicating that among the three rare earths studied, neither synergistic nor antagonistic effect played a part in the bioaccumulation process.

Bioconcentration factors:

The internal organs had much larger BCF than the other tissues. This was expected considering that the alimentary tract reflects normal transit of the substance. For this reason, this observation cannot be considered as an indication of bioaccumulation. Gills tissues retained the second highest concentration, suggesting that the gill is one of the main site of rare earth deposition in carp. By contrast, accumulation by muscles was minimal.

Validity criteria fulfilled:

not specified

Conclusions:

Lanthanum nitrate, gadolinium nitrate and yttrium nitrate do not show any potential for bioaccumulation in carp.

Executive summary:

The bioconcentration of the rare earth elements lanthanum, gadolinium and yttrium was studied in carp (Cyprinus carpio) during a 45-day semi-static experiment. In groups A, B, C, carps were exposed to stock solutions containing individual rare earths tested as their nitrates at final concentrations of 0.5 mg/L La, Gd or Y. In group D, carps were exposed to a mixed solution of the three rare earths containing 0.5 mg/L of each element. Controls were tested in parallel. Fish were sacrificed at time intervals and skeleton, muscles, gills and internal organs were dissected. Rare earth concentrations in fish tissues and water were determined using ICP-AES.

The bioaccumulation values (differences between the background concentration in unspiked fish tissue and the concentration in spiked tissue) in various tissues of carp, both in individual and mixed rare earth groups, increased with time. At the end of the 45 -day exposure period, the equilibrium was reached or approached. The bioaccumulation values for individual element solutions (Groups A,B,C) and those for mixed rare earth solution (Group D) did not differ significantly; indicating that among the three rare earths studied, neither synergistic nor antagonistic effect played a part in the bioaccumulation process.

After 45 days, the BCF values reported for the different rare earth were the followings:

* Lanthanum: Muscles: BCF = 3.2, Skeleton: BCF = 6.1, Gill: BCF = 18, Internal organs: BCF = 91.

* Gadolinium: Muscles: BCF = 3.5, Skeleton: BCF = 5, Gill: BCF = 14, Internal organs: BCF = 105.

* Yttrium: Muscles: BCF = 1.3, Skeleton: BCF = 3.8, Gill: BCF = 8, Internal organs: BCF = 54.

As a result, none of the studied rare earth show any potential for bioaccumulation.

Reference 2

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Remarks:

As recommended by the OECD guideline 305, this study was divided into two phases: a bioconcentration experiment followed by an elimination phase. Both were fully detailed in terms of methodology. The tested species are recommended in the guideline. The results were well-described. However, the GLP are not stated, and there is slight deviation compared to the experimental conditions preconised in the guideline. For the purpose of the analogy with cerium oxide, a focus will be made on the data of the cerium salt.

Qualifier:

equivalent or similar to guideline

Guideline:

EU Method C.13 (Bioconcentration: Flow-through fish test)

Deviations:

yes

Remarks:

regarding the test temperature and the biomass loading rate.

GLP compliance:

no

Radiolabelling:

no

Details on sampling:

- Sampling intervals/frequency for test organisms: Based on the table of results presented in the publication, fish were sampled after 3, 8, 15, 29, 36 and 43 days of exposure during the bioconcentration experiments. There is no detailed information on the sampling frequency during the elimination experiment except that fish were sampled 6 times (based on the figures provided in the articles).

- Sampling intervals/frequency for test medium samples: No data.

- Sample storage conditions before analysis: No data.

- Details on sampling and analysis of test organisms and test media samples (e.g. sample preparation, analytical methods): After sampling, the sacrificed fish were rinsed with distilled water and the surfaces of the fish bodies were dried. Careful dissection was made to divide the fish into various tissue categories: skeleton, muscles, gills and internal organs, which were removed into 50-mL beakers respectively. After weighing, these samples were digested with HNO3-HClO4 mixture and evaporated to near dryness. The residues were dissolved in 80 mL of 0.8 mol/L HCl and transferred to 8 x 200 mm columns packed with 1x8 strong cation exchangers (Dowex 50-X8). Then 90 mL of 1.75 mol/L HNO3 followed with 70 mL of 1.2 mol/L HCl were added to each column. The rare earth elements adsorbed by resins were finally eluted by 140 mL of 4 mol/L HCl. The elutes were evaporated to about 1 mL, the transferred to 10 mL volumetric flasks, and made up to volume with distilled water. The resultant solutions were subsequently used for analysis by ICP-AES.

Vehicle:

no

Details on preparation of test solutions, spiked fish food or sediment:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: The stock solution of rare earth elements was added into the aquaria with stirring.
- Controls: Two additional aquaria were tested in parallel.
- Evidence of undissolved material (e.g. precipitate, surface film, etc): No data.

Test organisms (species):

Cyprinus carpio

Details on test organisms:

TEST ORGANISM
- Common name: Carp.
- Age at study initiation: First-year juveniles.
- Average length at study initiation: 7 cm.
- Average weight at study initiation: 3.7 g.
- Feeding during test: The fish were fed on dry food every other day before each renewal.
No further data.

ACCLIMATION
- Acclimation period: 10 days.
- Acclimation conditions (same as test or not): in clean water (same as test).
- Health during acclimation (any mortality observed): The mortality rate was less than 5%.
No further data.

Route of exposure:

aqueous

Test type:

semi-static

Water / sediment media type:

natural water: freshwater

Total exposure / uptake duration:

43 d

Total depuration duration:

43 d

Hardness:

53-60 mg/L

Test temperature:

11-14°C

pH:

Water pH was modified to 6.0 with HNO3 and NaOH in order to minimize possible precipitation, ion exchange and adsorption of the rare earth elements.

Dissolved oxygen:

> 7 mg/L

TOC:

No data

Salinity:

Not applicable

Details on test conditions:

TEST SYSTEM
- Test vessel: Glass aquaria with a 60L-capacity filled with 30L water.
- Aeration: The test water was well aerated.
- Type of flow-through: Semi-static, and not flow-through test.
- Renewal rate of test solution: During the bioconcentration experiment, a volume of 20 liters of test solution in each aquarium was renewed every other day. In the elimination experiment, the non-contaminated water was renewed three times a week.
- No. of organisms per vessel: 60 fish in the aquaria exposed to the rare earth solution, 10 fish in the control aquaria.
- No. of vessels per concentration (replicates): 2.
- No. of vessels per control / vehicle control (replicates): 2.
- Biomass loading rate: 7.4 g/L in the aquaria exposed to the rare earth solution. 1.2 g/L in the control aquaria supposing that the water volume was the same as in the exposed aquaria.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Tap water was purified and dechlorinated through a water purifier mainly consisting of filter papers and activated carbon.
- Particulate matter: No data.
- Metals, Pesticides: No data.
- Chlorine: 7-8.5 mg/L.
- Alkalinity: 1.15-2.15 mmol/L.
- Ca/mg ratio: No data
- Conductance: 170 mOhms/CM.
- Holding medium different from test medium: The above described water was used as the diluent employed in all testing.
- Intervals of water quality measurement: No data.
- Intervals of test medium replacement: During the bioconcentration experiment, a volume of 20 liters of test solution in each aquarium was renewed every other day. In the elimination experiment, the non-contaminated water was renewed three times a week.

OTHER TEST CONDITIONS
- Adjustment of pH: Water pH was modified to 6.0 with HNO3 and NaOH in order to minimize possible precipitation, ion exchange and adsorption of the rare earth elements.
- Photoperiod: No data.
- Light intensity: No data.

RANGE-FINDING / PRELIMINARY STUDY
No data.

Nominal and measured concentrations:

The final concentrations of each element of the solution of rare earth elements were the following:
- [Ce] = 0.27 mg/L,
- [La] = 0.3 mg/L,
- [Nd] = 0.29 mg/L,
- [Pr] = 0.06 mg/L,
- [Sm] = 0.25 mg/L.

Reference substance (positive control):

no

Details on estimation of bioconcentration:

BASIS INFORMATION
- Measured/calculated logPow: Not applicable to inorganic substances.
No further data.

BASIS FOR CALCULATION OF BCF
The bioconcentration factor is calculated by dividing the concentration of rare earth elements in fish tissue (mg/kg) by the concentration of rare eart element in test water (mg/L).

Type:

BCF

Value:

0.22 L/kg

Basis:

organ w.w.

Remarks:

Muscles

Time of plateau:

43 d

Calculation basis:

other: Equilibria wa reached or approached

Remarks on result:

other: Conc.in environment / dose:[Ce] = 0.27 mg/L

Type:

BCF

Value:

5.94 L/kg

Basis:

organ w.w.

Remarks:

Skeleton

Time of plateau:

43 d

Calculation basis:

other: Equilibrium was reached or approached

Remarks on result:

other: Conc.in environment / dose:[Ce] = 0.27 mg/L

Type:

BCF

Value:

12.8 L/kg

Basis:

organ w.w.

Remarks:

Gills

Time of plateau:

43 d

Calculation basis:

other: Equilibrium was reached or approached

Remarks on result:

other: Conc.in environment / dose:[Ce] = 0.27 mg/L

Type:

BCF

Value:

608 L/kg

Basis:

organ w.w.

Remarks:

Internal organs

Time of plateau:

43 d

Calculation basis:

other: Equilibrium was reached or approached

Remarks on result:

other: Conc.in environment / dose:[Ce] = 0.27 mg/L

Elimination:

yes

Parameter:

other: Half-lives in skeleton for cerium unbound with fish tissues

Depuration time (DT):

0.24 d

Elimination:

yes

Parameter:

other: Half-lives in skeleton for cerium bound with fish tissues

Depuration time (DT):

23.9 d

Elimination:

yes

Parameter:

other: Half-lives in gills for cerium unbound with fish tissues

Depuration time (DT):

0.13 d

Elimination:

yes

Parameter:

other: Half-lives in gills for cerium bound with fish tissues

Depuration time (DT):

25.7 d

Elimination:

yes

Parameter:

other: Half-lives in muscles for cerium unbound with fish tissues

Depuration time (DT):

0.14 d

Elimination:

yes

Parameter:

other: Half-lives in muscles for cerium bound with fish tissues

Depuration time (DT):

25.7 d

Elimination:

yes

Parameter:

other: Half-lives in internal organs

Depuration time (DT):

8.66 d

Details on kinetic parameters:

Kinetics informations are available for the elimination phase:

- The elimination process in gills, muscles and skeleton could be divided into two periods: a fast elimination period followed by a slower loss period. after 8 days, the elimination rate became slowly and equilibria was reached. This elimination pattern suggests that rare earth elements may exist in two forms: one is unbound with fish tissues, another bound tightly in fish tissues. So the elimination curves can be fitted mathematically as the sum of two exponential functions according to two-compartment model: C(t) = Aexp(-mt) + B exp(-mt), where C(t) = the concentration of rare earth elements retained by the tissue at time t, A and B = intercepts of each exponential phase, m and n = slopes of each exponential phase.

- The elimination process in internal organs cal also be divided into two periods. In the first period, the concentration of rare eart elements increased and reached the maximum values at the end of the second day. In the second period, rare earth elements became to lose from internal organs and the kinetics of elimination can be described by the one-compartment model as follows: C(t) = C(i)exp(-kt), where C(i) = the maximum concentration in the internal organs, k = the biological elimination rate constant.

Details on results:

The BCF value in internal organs was higher than that reported for muscles, skeleton and gills. This was expected considering that the alimentary tract reflects normal transit of the substance. For this reason, this observation cannot be considered as an indication of bioaccumulation.

The results presented above concern cerium. The same data are available for lanthanum, neodymium, praseodymium and samarium. For further details, please see the publication.

Validity criteria fulfilled:

not specified

Conclusions:

Cerium trinitrate does not show any potential for bioaccumulation in fish.

Executive summary:

The bioconcentration and the elimination of rare earth elements was studied in carp (Cyprinus carpio). The bioconcentration phase corresponded to a 43-day semi-static experiment. Carps were exposed to a stock solution containing a mixture of cerium trinitrate (final [Ce] concentration = 0.27 mg/L), lanthanum trinitrate (final [La] concentration = 0.3 mg/L), samarium chloride (final [Sm] concentration = 0.25 mg/L) and praseodymium/neodymium nitrate (final [Nd] concentration = 0.29 mg/L, final [Pr] concentration = 0.06 mg/L). Controls were tested in parallel. Fish were sacrificed at time intervals and skeleton, muscles, gills and internal organs were dissected. Rare earth concentrations in fish tissues and water were determined using ICP-AES. When the equilibrium was reached, the elimination phase began according to the same experimental protocol than in the bioconcentration experiment.

After 43 days, the BCF values reported for cerium in muscles, skeleton, gills and internal organs were 0.22, 5.94, 12.8 and 608, respectively. The BCF value in internal organs was higher than that reported for muscles, skeleton and gills. This was expected considering that the alimentary tract reflects normal transit of the substance. For this reason, this observation cannot be considered as an indication of bioaccumulation.

The elimination process of cerium was different between muscles/skeleton/gills and internal organs. In the first group of tissues, cerium can exist under two forms: one unbound with fish tissues which is eliminated rapidly (half-lives between 0.13 and 0.24 days depending on the considered tissue), and, another bound tightly in fish tissues with a slower loss (half-lives between 23.9 to 25.7 days depending on the considered tissue). The elimination process of cerium in internal organs could also be divided into two periods. In the first, the concentration increased until reaching the maximum value at the end of the second day of the elimination experiment. This increase could be explained by the transportation from gills, muscles and skeleton to internal organs. In the second period, cerium was eliminated with a half-live of 8.66 days.

Reference 3

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

This publication described a microcosm experiment and was fully described with respect to the experimental conditions and the results. However, the GLP are not stated and there is no reference to international guideline. For the purpose of the analogy with cerium oxide, a focus will be made on the data of the cerium salt.

Qualifier:

no guideline followed

Principles of method if other than guideline:

This study used a static laboratory aquatic microcosm to assess the distribution of rare earth elements in the different environmental compartments (water, sediment and biota) and their potential for bioaccumulation in different trophic groups including fish.

GLP compliance:

no

Radiolabelling:

no

Details on sampling:

- Sampling intervals/frequency for test organisms and for test medium samples: Water, sediment, duckweeds and daphnids were sampled after 0.5, 1, 2, 4, 8, 12 and 16 days of exposure, while shellfish and goldfish were sampled after 2, 4, 8, 12 and 16 days.

- Sample storage conditions before analysis: No data.

- Details on sampling and analysis of test organisms and test media samples (e.g. sample preparation, analytical methods):
* 5 mL water samples were filtered through 0.45 µm membranes.
* Sediment samples were washed by deioned water and dried by air, then 0.5 g sediments were digested with Na2O2 under 700°C and passed through cation-exchange columns.
* 50 mg duckweeds, 30 daphnids, 1 shellfish and 1 goldfish were digested with the mixture of conc. HNO3 and HClO4 respectively.
The final solutions of all these samples were brought to 5 mL with 7 % HCl and determined by ICP-AES. All samples were treated in duplicate.

Vehicle:

no

Details on preparation of test solutions, spiked fish food or sediment:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: After the system has equilibrated for one week, the experiment was initiated by spiking mixed rare earth solution into the aquarium.
- Controls: Yes, without spiked rare earth elements.
- Evidence of undissolved material (e.g. precipitate, surface film, etc): No data.

Test organisms (species):

Carassius auratus

Details on test organisms:

TEST ORGANISMS:

Below, are the information available on the fish species tested :
- Common name: Goldfish.
- Length at study initiation: 5 cm body length.
- Feeding during test: Fish were fed a commercial fish food.
No further data.

It should be noticed that other aquatic species were tested in this study:

* Sperollela polyrrhiza:
- Common name: Duckweed.
- Source: cultured in the State Key Laboratory of Pollution Control and Resource Reuse, Department of Environmental Science and Engineering, Nanjing University, China.

* Daphnia magna:
- Common name: Water flea.
- Methode of breeding: cultured in the State Key Laboratory of Pollution Control and Resource Reuse (Nanjing University) in HB-4 aqueous medium.
- Feeding during test: Daphnids were fed unicellular green algae (Chlorella pyrenoidosa).

* Bellamya aeruginosa:
- Common name: Shellfish.
- Source: cultured in the State Key Laboratory of Pollution Control and Resource Reuse (Nanjing University).

ACCLIMATATION:

All these organisms were acclimated to laboratory conditions one week prior to the experiment.
No further data.

Route of exposure:

other: Rare earth elements were spiked in microcosms containing water, sediments and biota representing different trophic levels.

Test type:

static

Water / sediment media type:

natural sediment: freshwater

Total exposure / uptake duration:

16 d

Total depuration duration:

0 d

Hardness:

No data

Test temperature:

22 ± 1°C

pH:

6.5 - 6.8

Dissolved oxygen:

No data

TOC:

No data

Salinity:

Not applicable

Details on test conditions:

TEST SYSTEM
- Test vessel: Aquatic microcosm.
- Type: open.
- Material, size, headspace, fill volume: 20 x 50 x 50 cm aquarium containing 50 L filtered lake water and a 2-cm layer of sediments on the bottom
- Aeration: The aquaria were aerated during the experiment.
- Type of flow-through: Static, and not flow-through test.
- Renewal rate of test solution (frequency/flow rate): Not applicable (static test).
- No. of organisms per vessel: 20 g duckweeds, 30 shellfish, 400 caged daphnids, 15 goldfish.
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1
- Biomass loading rate: No data

TEST MEDIUM / WATER / SEDIMENTS PARAMETERS
- Source/preparation of dilution water: Water and sediment were collected from a typical eutrophic lake (Nanjing, china). Water was filtered by acid-washed 0.45 µm. Whatman membrane and sediments samples were dried by air and weighed before adding into the aquarium.
No further data except that the physico-chemical properties of the water and the sediments used in this study were reported in a non available confidential report.

OTHER TEST CONDITIONS
- Adjustment of pH: pH kept at 6.5 to 6.8 in order to avoid precipitation which occurs under alkaline conditions.
- Photoperiod: 12 hours light / 12 hours dark.
- Light intensity: No data.

RANGE-FINDING / PRELIMINARY STUDY
No data.

Nominal and measured concentrations:

The mixed rare earth solution was spiked at a concentration of 1 mg/L with 1 mg/mL of each of the five rare earth elements.

Reference substance (positive control):

no

Details on estimation of bioconcentration:

BASIS INFORMATION
- Measured/calculated logPow: Not applicable to inorganic substances.
No further data.

BASIS FOR CALCULATION OF BCF
Bioconcentration coefficients were calculated using the following equation:
Bioconcentration coefficient = (Cs – Cs0) / Cw
Where: Cs = rare earth concentration in the considered species, Cs0 = rare earth concentration in the same species in the control treatment, Cw = rare earth concentration in test water.

Time of plateau:

16 d

Remarks on result:

other: No bioconcentration effect of cerium was detected in goldfish

Time of plateau:

16 d

Remarks on result:

other: No bioconcentration effect of cerium was detected in daphnids

Time of plateau:

16 d

Remarks on result:

other: No bioconcentration effect of cerium was detected in shellfish

Type:

BCF

Value:

214.3 dimensionless

Time of plateau:

16 d

Remarks on result:

other: BCF value calculated for duckweeds

The results above presented concerned cerium. The same information are also available on lanthanum, samarium, gadolinium and yttrium. Based on these data, it shoud be noted that no bioconcentration effect was observed in the fish Carassius auratus regardless the rare earth considered. For further details, please see the publication.

Furthermore, information are given concerning the distribution of the rare earth in the different environmental compartments. For cerium, the results are the followings: 92.48% in sediments, 7.06% in water and 0.46% in biota.

Validity criteria fulfilled:

not specified

Conclusions:

Cerium chloride does not show any potential for bioaccumulation in fish.

Executive summary:

The distribution of rare earth elements in the different environmental compartments (water, sediment and biota), and their potential for bioaccumulation in different trophic groups, were studied in a static laboratory experiment using aquatic microcosms. Duckweeds (Sperollela polyrrhiza), daphnids (Daphnia magna), shellfish (Bellamya aeruginosa) and goldfish (Carassius auratus) were exposed for 16 days to a rare earth solution (at 1 mg/L) containing a mixture of cerium trichloride, lanthanum trinitrate, samarium trichloride, digadolinium trioxide and diyttrium trioxide. Rare earth concentrations in water, sediments and biological samples were determined using ICP-AES. All the rare earth elements distributed mainly in sediments (82.01 to 97.64%), then in water (1.93 to 16.97%), and for a minor part in biota (0.46 to 1.02%). None of the rare earth tested showed any bioconcentration effect in goldfish, shellfish and daphnids, with the exception of yttrium exhibiting a bioconcentration coefficient of 430.5 in daphnids. The bioconcentration coefficients measured in duckweeds varied between 103.7 and 992.7 depending on the considered rare earth (cerium: 214.3).

Description of key information

Using a weight-of-evidence approach, cerium dioxide does not show any potential for bioaccumulation.

Additional information

Reliable bioaccumulation data in fish are only available on soluble salts of cerium as nitrate (Hao et al. 1996) and chloride (Yang et al. 1999). Both studies, scored as reliability 2 according to Klimisch, are considered in a weight-of-evidence approach to conclude on the bioaccumulation potential of cerium dioxide. The reasoning applied in this context is detailed hereafter. The first pre-requisite is to bring evidences that soluble and insoluble forms of a same rare earth show similar behaviour in terms of bioaccumulation in fish. In this context, a supporting study, also scored as reliability 2, is provided (Qiang et al. 1994). By comparing the results of this study with those of Yang et al. (1999), it could be concluded that soluble and insoluble forms of both yttrium and gadolinium show similar bioaccumulation behaviour. For yttrium, no bioconcentration effect was observed in Carassius auratus for the insoluble oxide form (Yang et al. 1999). For the soluble nitrate form, the BCF values measured in Cyprinus carpio ranged between 1.3 and 54 (depending on the considered organs, i.e. skeleton, muscles, gills and internal organs); suggesting no potential for bioaccumulation (Qiang et al. 1994). For gadolinium, Yang et al. (1999) did not detect any bioconcentration effect of the insoluble oxide form in Carassius auratus. And, the BCF values of the soluble nitrate form measured in Cyprinus carpio ranged between 3.5 and 105 (depending on the considered organs, i.e. skeleton, muscles, gills and internal organs); suggesting no potential for bioaccumulation (Qiang et al. 1994). Data on both rare earths thus indicated that soluble and insoluble forms behaved similarly in terms of bioaccumulation in fish. The same process could be expected for cerium. Cerium dioxide shows low water solubility (< 0.123 µg/L) and is thus less bioavailable for fish than soluble salts. Based on the evidence reported for yttrium and gadolinium, it can be expected this insoluble form of cerium (i.e. oxide) should not show any potential for bioaccumulation, as the soluble ones (i.e. chloride and nitrate).