Neodymium trinitrate

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

other: Experimental study on the neodymium moiety

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Although the study gives information on BCF in several organs of carp, no standard protocol was followed for this experiment.

Qualifier:

no guideline followed

Principles of method if other than guideline:

The bioconcentration and elimination of neodymium was studied in carp at different times of exposure. The uptake and depuration durations were 43 and 21 days, respectively.

GLP compliance:

no

Radiolabelling:

no

Details on sampling:

- Sampling intervals/frequency for test organisms and medium:
* uptake study: 3, 8, 15, 29, 36 and 43 d
* elimination study: 1, 3, 8, 18 and 36 d

Vehicle:

no

Test organisms (species):

Cyprinus carpio

Details on test organisms:

TEST ORGANISM: Common name: carp- Age at study initiation (mean and range, SD): first year juveniles- Length at study initiation (length definition, mean, range and SD): 7.0 cm- Weight at study initiation (mean and range, SD): 3.7 g- Feeding during test: fish were fed dry food before each renewal
ACCLIMATION- Acclimation period: 10 d

Route of exposure:

aqueous

Test type:

semi-static

Water / sediment media type:

not specified

Remarks:

freshwater

Total exposure / uptake duration:

43 d

Total depuration duration:

21 d

Hardness:

53-60 mg CaCO3/L

pH:

6.4-7.4

Dissolved oxygen:

>70 mg/L

Salinity:

7.0-8.5 mg Cl/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 60 L glass aquarium with 30 L test solution
- Renewal rate of test solution: a volume of 20 L of test solution was renewed every other day
- No. of organisms per vessel (test concentration): 60
- No. of organisms per vessel (control): 10
- No. of vessels per concentration (replicates): 2
- No. of vessels per control / vehicle control (replicates): 2
elimination study
- No. of organisms per vessel (test concentration): 30
- No. of vessels per concentration (replicates): 2
TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: tap water
- Chlorine: 7.0-8.5 mg/L
- Total alkalinity: 1.15-2.15 mmol/L
- Conductivity: 170 (mOhm*cm)
-OTHER TEST CONDITIONS
- Adjustment of pH: yes (modified to 6.0 with HNO3 and NaOH
- Test concentration: chosen concentration was close to the concentration in a natural aquatic environment
ELIMINATION EXPERIMENTS:
When equilibrium was reached, 30 fishes of each test aquarium were placed in non-contaminated water. This was renewed three times a week to monitor REEs elimination according to the same experimental protocols as during the bioconcentration study.

Nominal and measured concentrations:

Nominal and measured concentrations
Mixture of:
0.3 mg/L Lanthanum
0.27 mg/L Cerium
0.29 mg/L Neodymium
0.06 mg/L Praseodymium
0.25 mg/L Samarium

Reference substance (positive control):

no

Details on estimation of bioconcentration:

BCF is derived on concentration of RE in fish tissue (mg/kg) divided by concentration of RE in test water.

Type:

BCF

Value:

0.62 L/kg

Basis:

organ w.w.

Remarks:

muscle

Time of plateau:

43 d

Calculation basis:

steady state

Remarks:

concentration in fish tissues (mg/kg) divided by concentration in test medium (mg/L)

Remarks on result:

other: time of plateau, see table 2

Remarks:

Conc.in environment / dose:0.29 mg/L

Type:

BCF

Value:

2.28 L/kg

Basis:

organ w.w.

Remarks:

skeleton

Time of plateau:

43 d

Calculation basis:

steady state

Remarks:

concentration in fish tissues (mg/kg) divided by concentration in test medium (mg/L)

Remarks on result:

other: time of plateau, see table 2

Remarks:

Conc.in environment / dose:0.29 mg/L

Type:

BCF

Value:

9.73 L/kg

Basis:

organ w.w.

Remarks:

gills

Time of plateau:

43 d

Calculation basis:

steady state

Remarks:

concentration in fish tissues (mg/kg) divided by concentration in test medium (mg/L)

Remarks on result:

other: time of plateau, see table 2

Remarks:

Conc.in environment / dose:0.29 mg/L

Type:

BCF

Value:

451 L/kg

Basis:

organ w.w.

Remarks:

internal organs

Time of plateau:

43 d

Calculation basis:

steady state

Remarks:

concentration in fish tissues (mg/kg) divided by concentration in test medium (mg/L)

Remarks on result:

other: time of plateau, see table 2 (internal organs reflect the normal transit of the substance rather than indication of bioaccumulation)

Remarks:

Conc.in environment / dose:0.29 mg/L

Elimination:

yes

Parameter:

DT50

Depuration time (DT):

6.3 d

Details on kinetic parameters:

Elimination experiments:The elimination process of light REEs in gills, muscle and skeleton were similar and could be divided into two periods: a fast elimination period followed by slower loss period. After 8-day elimination experiment, the elimination rate became slow and equilibria were reached. This elimination pattern suggests that the light REEs which bioconcentrated in fish tissues may exist in two forms, one is unbound REEs which accounted for more than 50%-70% of total tissue REEs concentrations, another is the REEs which are bound tightly in fish tissues. Half-lives of the unbound form and the bound form that fitted mathematically a two-compartment model, are given in table 3.The elimination process of REEs in internal organs can also be divided into two periods, in the first period the concentrations of REEs increased and reached the maximum values at the end of the second day. In the second period, REEs were lost from internal organs and the kinetics of elimination can be described by the one-compartment model. Half-life (d) for neodymium: 6.3 d with R=0.99 (R= correlation coefficient).

Table 1: background values of neodymium in Cyprinus carpio:

tissue	Nd concentration (mg/kg wet weight)
gills	0.04
muscle	0.03
skeleton	0.09
internal organs	0.50

Large variations of BCFs are observed for different tissues, the order of bioconcentration factors is: internal organs >> gills > skeleton > muscle. 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.

Table 2: Variations of BCFs of neodymium in Cyprinus carpio exposed to mixed REEs at pH 6.0 (only data for neodymium shown here)

tissue	Bioconcentration Factor (L/kg wet weight)
	3 d	8 d	15 d	29 d	36 d	43 d
gills	2.94	10.9	3.69	7.15	11.2	9.73
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
internal organs	104	131	315	634	32.0	451

Table 3: The biological half-lives in the different tissues of Carp are:

tissue		half-lives days (unbound form)	Half-lives days (bound form)	R*
Skeleton		0.43 (77.8%)	99 (22.2%)	0.98
gills		0.23 (87.0%)	12.4 (13.0%)	0.99
muscle		0.10 (96.4%)	86.6 (3.6%)	0.98

R= The correlation coefficient of releasing equations according to a two-compartment model

Validity criteria fulfilled:

yes

Conclusions:

In this study, carp (Cyprinus carpio) were exposed to a mixture of light REEs for 43 days. BCF values were calculated for muscle, skeleton, gills, internal organs, ranging from 0.62, 2.28,9.73 and 451 L/kg ww, 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 the normal transit of the substance. For this reason, this observation cannot be considered as an indication of bioaccumulation. Based on the BCF values calculated for other organs (i.e., skeleton, gills, muscle), neodymium presents a low potential for bioaccumulation in carp.

Description of key information

BCF for neodymium were determined in a 43-day experiment with carp (Cyprinus carpio). Maximum BCF values for muscle tissue, skeleton, and gills were 0.62, 2.28 and 9.73 L/kg ww, respectively. A higher BCF was found for the internal organs than for other organs (i.e. muscle, skeleton, gills). Internal organs serve as important site for detoxification and storage for rare earth elements. The BCF values for internal organs are thus not considered as a good indication of the bioconcentration potential, since the alimentary tract reflects the normal transit of the substance.

Additional information

No data is available on neodymium trinitrate itself. However, it was considered that the laboratory study of Sun et al. (1996) that exposed carp (Cyprinus carpio) to a mixture of rare earth elements, among which neodymium, was relevant and informative of the bioaccumulation behaviour of neodymium dissolved from any neodymium substance. This study, scored as Klimisch 2, was thus flagged as a key study and revealed a low bioaccumulation potential for neodymium in aquatic organisms.