Neodymium oxide

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

bioaccumulation in aquatic species: fish

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

In accordance with section 1 of REACH Annex XI (testing does not appear scientifically necessary), the bioaccumulation study (required in section 9.3.2.) does not need to be conducted as the substance can be predicted not to be bioaccumulative based on analogy with neodymium nitrate. The available data is adequate for classification and labeling purposes and PBT assessment is not required for inorganic substances so no further testing is required.

Reference 2

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:

other: Non GLP study conducted to a non guideline method and read-across from an analogous substance. Literature paper considered inherently reliable.

Qualifier:

no guideline followed

Principles of method if other than guideline:

The bioconcentration and the elimination of several rare earth compounds, among which a mixed solution of neodymium and praseodymium nitrates, were studied in carp (Cyprinus carpio). As recommended by the OECD guideline 305, this study was divided into two phases: a bioconcentration experiment followed by an elimination phase. The tested species are recommended in the guideline.

GLP compliance:

no

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
PrNd(NO3)6.nH2O
All the reagents were all of analytical grade.

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:

Tap water was purified and dechlorinated through a purifier mainly consisting of filter papers and activated carbon. The obtained water was used as the diluent employed in all testing. The stock solution of rare earth elements was added into the aquaria with stirring. Two additional control aquaria were tested in parallel.

Test organisms (species):

Cyprinus carpio

Details on test organisms:

Common name: Carp.
All fish were first year juveniles
Average length = 7.0 cm
Average weight = 3.7 g
Feeding during test: The fish were fed on dry food every other day before each renewal.
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%.

Route of exposure:

aqueous

Test type:

semi-static

Water / sediment media type:

natural water: freshwater

Total exposure / uptake duration:

43 d

Total depuration duration:

8 d

Hardness:

53-60 mg/L

Test temperature:

11 to 14°C

pH:

6.4 to 7.4

Dissolved oxygen:

> 7.0 mg/L

Details on test conditions:

Bioconcentration
Two glass aquariums with 60 litre capacity were used as containers for duplicate experiments. the fish were divided into two groups of 60. Each group of fish was placed into an aquarium containing 30 litres of water. Stock solutions were added, with stirring. The final concentration of the element in the test aquariums was 0.29 Cw mg/L. The test water was well aerated and water temperature was maintained at 11 -14°C by a temperature controller. Water pH was modified to 6.0 with HNO3 and NaOH in order to minimise possible precipitation ion exchange and adsorption. A volume of 20 litres of test solution in each aquarium was renewed every other day. Fish were fed on dry food prior to each renewal. Bioconcentration experiments were carried out over a 43 -day period. Two additional aquariums eacgheach containing 10 fish served as controls and were also used for analysis of the background levels of the substance in carp.Fish were sacrificed at time intervals from each of the test groups. The sample 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, muscle, gills and internal organs were removed into 50 ml beakers respectively.

Elimination
When equilibrium was reached 30 fish of each test aquarium were placed in non-contaminated water renewed three times a week to monitor elimination according to the same experimental protocols as during the bioconcentration study.

Nominal and measured concentrations:

Concentrations were based on nominal values only. The final concentrations of each element of the solution of rare earth elements were the following
- [Nd] = 0.29 mg/L,
- [Pr] = 0.06 mg/L.

Details on estimation of bioconcentration:

After weighing samples were digested with HNO3-HClO4 mixtures and evaporated to near dryness. The residues were dissolved in 80 ml of 0.8 mol/L HCl and transferred to 8x200 mm columns packed with 1x8 strong cation exchanges (Dowex 50-X8). Then 90 ml of 1.75 mol/L HNO3 followed with 70 ml 1.2 mol/L HCl were added to each column. Test substance adsorbed by resins were finally eluted by 140 ml of 4.0 mol/L HCl. The elutes were evaporated to ca. 1 mL, then transferred to 10 mL volumetric flasks, and made up with distilled water. The resultant solutions were subsequently used for analysis by ICP-AES.
The bioconcentration factor is calculated by dividing the concentration of rare earth elements in fish tissue (mg/kg) by the concentration of rare earth element in test water (mg/L).

Details on results:

Bioconcentration Factors for neodymium L/kg wet weight
Tissue 3d 8d 15d 29d 36d 43d
Muscle 0.48 0.48 0.38 0.86 0.14 0.62
Skeleton 0.35 0.52 0.79 0.86 0.24 2.28
Gills 2.94 10.9 3.69 7.15 11.2 9.73
Internal organ 104 131 315 634 32.0 451

At the end of the 43-day exposure period equilibrium was considered to have been reached. It is important to note the BCF values in internal organs were 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 the test substance in gills, muscle and skeleton can be divided into two periods; a fast elimination period following a slower loss period. During an 8-day elimination experiment the elimination rate slowed and equilibrium was reached. The elimination pattern suggests that light rare earth elements that bioconcentrate in fish tissues may exist in two forms: one is unbound (accounting for 50-70 % of total concentrations found in tissues) and the other which is tightly bound in the tissue.

The elimination process of rare earth elements in internal organs can also be divided into two periods. In the first period concentrations increased and reached a maximum at the end of the second day. In the second period the concentrations began to decrease and the kinetics of elimination can be described by the one-compartment model as follows:

C(t) = C(i) e-kt

where
C(i) = the maximum concentration in the internal organs
k = the biological elimination rate constant

A first-order process has been demonstrated during the second period of elimination in internal organs. An increasing period before elimination can be explained by the transportation of the rare earth elements from gills, muscle and skeleton to internal organs. When equilibrium was not reached the rate of elimination in gills, muscle and skeleton was faster than in internal organs.

Conclusions:

The study shows that some bioaccumulation of light rare earth elements can occur but that elimination processes reduce the bioaccumulation factors over a period of time. The highest BCF value observed during the study for neodymium was 634 in internal organs after 29 days and this reduced to 451 by the end of the study at 43 days. For the other studied tissues, the BCF values were the followings:
Muscle: BCF = 0.14 to 0.86
Skeleton: BCF = 0.24 to 2.28
Gills: BCF = 2.94 to 11.2
It is thus important to note the BCF values in internal organs were higher than that reported for 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.
The CLP threshold to consider a substance as bioaccumulative is BCF ≥ 500. The REACH criteria for PBT and vPvB as stated in Annex XIII give cut-off BCF values of 2000 and 5000 respectively. and iIt is therefore considered reasonable to assume that neodymium trinitrate, and by read-across the insoluble neodymium oxide, should not be considered to meet either of these criteria on the basis of the available data.

Executive summary:

Literature data exists on the bioaccumulation of soluble salts of light rare earth elements. Data on neodymium nitrate can be used to provide an estimate of the bioaccumulation potential of neodymium oxide.

The study shows that some bioaccumulation of light rare earth elements can occur but that elimination processes reduce the bioaccumulation factors over a period of time.

The highest BCF value observed during the study for neodymium was 634 in internal organs after 29 days and this reduced to 451 by the end of the study at 43 days. For the other studied tissues, the BCF values were the followings:

Muscle: BCF = 0.14 to 0.86

Skeleton: BCF = 0.24 to 2.28

Gills: BCF = 2.94 to 11.2

It is thus important to note the BCF values in internal organs were higher than that reported for 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.

The CLP threshold to consider a substance as bioaccumulative is BCF ≥ 500. The REACH criteria for PBT and vPvB as stated in Annex XIII give cut-off BCF values of 2000 and 5000 respectively and. iIt is therefore considered reasonable to assume that neodymium trinitrate, and by read-across the insoluble neodymium oxide, should not be considered to meet either of these criteria on the basis of the available data on an analogous substance.

Description of key information

No bioaccumulation data are available on insoluble salts of neodymium but literature data provide information on the soluble salt neodymium nitrate.

A BCF value of 634 was recorded in internal organs after 29 days, with BCF values reducing over time and reaching 451 by the end of the study at 43 days. For the other studied tissues, the BCF values were the followings:
Muscle: BCF = 0.14 to 0.86
Skeleton: BCF = 0.24 to 2.28
Gills: BCF = 2.94 to 11.2
It is thus important to note the BCF values in internal organs were higher than that reported for 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. The half-life for internal organs was calculated as 6.30 days. Neodymium nitrate is therefore eliminated from fish and does not readily bio-concentrate. By analogy to neodymium nitrate, neodymium oxide is unlikely to bioaccumulate, and furthermore being poorly water soluble it is expected to be less bioavailable than the soluble salt tested.