Lanthanum oxide

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

10 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

1 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

1 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

100 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

15.5 mg/kg sediment dw

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

15.5 mg/kg sediment dw

Assessment factor:

100

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

18.9 mg/kg soil dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

156 mg/kg food

Assessment factor:

90

Additional information

Aquatic data for the PNEC derivation

Endpoint	Value	Concentration measured	Substance	Reference
Acute Fish	LC50 96 h, LC0 > 100 mg/l (LR)^1	No	La2O3	Bazzon, 2000
Acute Fish	LC50 96 h, LC0 > 100 mg/l (LR)	No	Ce2O3	Bazzon, 2000
Acute Daphnia	EC50 48 h, EC0 > 100 mg/l (LR)	Not detected	La2O3	Seyfried, 2007
Acute Daphnia	EC50 48 h, EC0 > 100 mg/l (LR)	Not detected	CeO2	Bätscher, 2007a
Acute Algae growth rate	ErC50, ErC10 > 100 mg/l, 91 mg/L (LR)	No	CeO2	Bätscher, 2007b
Long term daphnia reprod, 21 d	NOEC > 100 mg/L (LR)	46 microg L/l 54 micro-g La2O3/L	La2O3	Höger 2009
Long term daphnia reprod, 21 d	NOEC > 100 mg/L (LR)	Not detected	CeO2	Höger 2009
Long term fish mortality 14 d	NOEC 0.26 mg/l mort. 0.3 mg/L as La2O3	0.26 mg/L as La 0.3 mg/L as La2O3	La2Cl3	Borgers 1995
Algae growth rate	72 h EC50: 16 mg/l as La 18.7 mg/l as La2O3 72 h EC10: 1.3 mg/l as LA 1.5 mg/L as La2O3	Yes	La2Cl3	Borgers 1995
Daphnia acute	EC50 48 h: 1.18 mg/l as La 1.4 mg/L as La2O3	Yes	La2Cl3	Barry and Meehan, 2000
Daphnia 21 d	NOEC: 0.1 mg/L As La 0.12 mg/l as La2O3	Yes	La2Cl3	Borgers, 1995

1 LR : Loading rate

PNEC derivation

Aquatic compartment:

Selection of the starting point:

For lanthanum oxide or the very similar rare earth oxide Cerium oxide as substances with very low water solubility short term tests for 3 trophic levels using water accommodated fractions and maximum loading rates of 100 mg/L are available as well as a long term 21-d Daphnia reproduction studies with lanthanum oxide and cerium dioxide. In the 21 -day Daphnia study with lanthanum oxide the lanthanum concentration was measured and corresponded to a mean saturation concentration of 46 micro-g La/L or 54 micro-g lanthanum oxide/L. This is well in line with the maximum water solubility at pH 6.29 to 6.85 of 69.6 micro-g/L.

The lowest NOEC as loading rate was the Algae EC10 of 91 mg/L performed with cerium dioxide. The effect in this study was however rather due to a depletion of phosphate in the test medium than a direct toxic effect. It can therefore be assumed that the NOEC for algae is also greater than 100 mg/l loading rate. As for soluble lanthanum salts daphnia was the most sensitive organism in long term studies, the NOEC loading rate of the 21 -day daphnia study is used as the starting point for the PNEC derivation. As long term toxicity data for all three trophic levels are available for the soluble lanthanum chloride and sugggest that daphnids are the most sensitive species, an asessment factor of 10 seems to be justified (ECHA R10, 2008), resulting in a PNEC_{aquatic-freshwater}of 10 mg/L.

For the marine assessment a factor of 100 in accordance with ECHA R.10, 2008 wasapplied to this value resulting in a PNEC_{aquatic-marine}of 1 mg/L.

For intermittent releases an assessment factor of 100 was applied to the lowest LC50 value of > 100 mg/L loading rate, resulting in a PNEC_{aquatic-intermittent} of 1 mg/L.

In parallel the relevant aquatic studies available for lanthanum chloride, a soluble Lanthanum compound were reviewed and compared to the water solubility of lanthanum oxide of 69.6 micro-g/L. For lanthanum chloride long term toxicity data for three trophic levels, algae, daphnia and fish are available. From both the short term and long term data invertebrates seem to be the most sensitive species. A 21-d Daphnia study revealed a NOEC of 0.1 mg/L of La which would correspond to 0.13 mg/L of Lanthanum oxide. As this value is above the water solubility of Lanthanum oxide no toxic effect to aquatic organisms is expected at saturation. This was corroborated by the 21-day daphnia study with lanthanum oxide at a loading of 100 mg/L. Lanthanum oxide is therefore not expected to exert any considerable toxicity to aquatic organisms and the PNEC is a conservative estimate.

The PNEC derived from laboratory data is compared to baseline background concentrations of lanthanum in water that can be derived from the FOREGS data base. The median water concentration from the 808 data points was 0.034 micro-g/L (SE 0.027), the mean 0.22 micro-g/L (SD 0.77), the maximum was 16 micro-g/L and a number of values were below the detection limit of 0.002 micro-g/L. The 90^thpercentile was 0.5 micro-g/L and the 10^thpercentile 0.0054 micro-g/L (Salminen et al. 2005).

PNEC STP

No data were available on lanthanum oxide. For lanthanum chloride a NOEC of a respiratory inhibition test is available (70 mg La/L corresponding to 82 mg/L of La2O3. A respiration inhibition test with cerium dioxide on the other hand showed no inhibirion of respiration at a loading rate of 1000 mg/L. Due to the comparably low solubility of lanthanum oxide and ceriumdioxide it can reasonably be concluded that lanthanum oxide will also not have any cosiderable toxicity to sewage treatment plant organisms. From the study on cerium dioxide a PNEC_STP of 100 mg/L was derived using an assessment factor of 10 in accordance with ECHA guidance R10.

PNEC Sediment

One long term sediment test with Chironomus ripariuslarvae according to current guidelines and GLP is available for lanthanum trichloride hexahydrate. The NOEC in this test was≥1317 mg La/kg dry weight corresponding to≥1545 mg Lanthanum oxide per kg dw. This was the highest dose tested in the assay that did not lead to any adverse effects. This NOEC is taken forward for the assessment of lanthanum oxide as well. As lanthanum chloride has a much higher water solubility, it is likely to have a higher bioavailability to sediment organisms and can be regarded as a worst case surrogate. The speciation in sediment will in any case also be dependent on the environmental or experimental conditions. As only one test is available an assessment factor of 100 is used leading to a PNEC_{sediment freshwater} of 15.5 mg/kg dw (13.17 mg La/kg dw). Formally, according to ECHA R.10, 2008 for marine sediments a factor of 1000 would be applied to one freshwater long term sediment study leading to a PNEC_{sediment marine water} of 1.6 mg/kg dw (1.3 mg La/kg dry weight). It can however reasonably be expected that marine organisms are adapted to higher salt concentrations and will probably be similarly adapted to background concentrations of lanthanum. Therefore an assessment factor of 100 is considered sufficient for the marine sediment as well for the initial assessment.

The baseline sediment concentrations for lanthanum as derived from the FOREGS database (848 data points) (Salminen et al., 2005) are as follows: median concentration 32.5 mg/kg (SE 1.5), mean concentration: 41 mg/kg (SD 44.9), maximum 553 mg/kg, 90^thpercentile: 385, 10^thpercentile: 15.7.

It should be noted that the baseline sediment concentrations as derived from the FOREGS data base are of the same order of magnitude or higher and it can reasonably be assumed that sediment organismsin the field are adapted to higher concentrations of lanthanum. Furthermore it is likely that lanthanum compounds adsorbed to sediment are in an insoluble form and have a low bioavailability. As no effects were observed at a limit concentration with a soluble lanthanum salt there is at present little concern for possible adverse effects on sediment organisms.

PNEC soil

The lowest NOEC for terrestrial toxicity was observed for plants (Zea mays) with lanthanum trinitrate with a NOEC of 107 mg La/kg dw (corresponding to 126 mg/kg dw lanthanum oxide). However, it should be considered that the nitrate anion could have contributed to the toxicity in this case. Additionally studies for cerium dioxide on earthworms (14 -day acute), terrestrial plants and soil microorganisms consistently showed no toxicity at the maximum concentration of 1000 mg/kg dw. NOEC values from additional long-term toxicity tests of more than three species of three trophic levels (earthworms, anthropods, plants and microorganisms) are available for lanthanum compounds an assessment factor of 10 can be used according to ECHA R.10, 2008. Due to the low solubility of lanthanum oxide it can reasonably be assumed that the PNEC soil will be considerably higher, which is also corroborated by the studies with cerium oxide. Furhtermore it should be considered that that this derived PNEC_soilvalue is smaller than most of the mean background values of lanthanum concentrations in soil in different regions as described in the literature (Tyler, 2004, Rikken, 1995) and reported in the FOREGS data base (Salminen, 2005). Tyler (2004) reports background concentrations of lanthanum in the earth crust of 35 mg La/kg, and a mean concentration in Japanese soils of 18 mg La/kg (n=77), in Chinese soil of 44 mg La/kg (n=44), and in Swedish forest topsoil of 5.5 to 33.2 mg/kg. Ricken (1995) reported mean background concentrations worldwide as 26.1 mg La/kg. Redling (2006) reported mean soil concentrations of 2.7 to 24.3 mg La/kg in Australian soils, 1.2 to 51.1 mg La/kg in Japanese soils, 1.2 to 51.1 mg La/kg in Chinese soils, 17.8 mg La/kg in Swiss Forest Soil, 14.5 to 40.1 mg La/kg in German farm soils, 4.8 to 46.6 mg La/kg in German forest soils and 5 to 50 mg La/kg in Dutch soils. The FOREGS data base reports following concentrations:

Soil samples (number of samples)	Mean mg/kg soil (SD)	Median mg/kg soil (SE)	Maximum mg/kg soil	90^thpercentile mg/kg soil	10^thpercentile mg/kg soil
Europe humus (367)	3.3 (5.3)	1.7 (0.28)	52.5	37	310
Europe subsoil (788)	27.7 (16.1)	25.6 (0.57)	155	47	10
Europe topsoil (843)	25.9 (15.8)	23.5 (0.55)	143	43.7	9.1

It can therefore be reasonably assumed that terrestrial organisms in the field are adapted to higher concentrations of lanthanum. Furthermore it is likely that lanthanum oxide adsorbed to soil are as an insoluble form will have a low bioavailability.

PNEC oral

For avian toxicity one repeated dose 28-day dietary study with the soluble lanthanum salt lanthanum trichloride in Japanese quails is available that did not show adverse treatment related effects at the maximum dietary concentration of 56.6 mg La/kg food (corresponding to 66.4 mg La₂O₃/kg food). With and assessment factor of 30 this would lead to a PNEC of 1.9 mg La/kg food or 2.2 mg La₂O₃/ kg food. The NOAEL of the repeated dose 90-day oral feeding study in rats with lanthanum carbonate was≥14000 mg/kg diet with no treatment related adverse effects observed at the highest dose tested. With an assessment factor of 90 (ECHA R.10, 2008) this leads to PNEC of 156 mg/kg food. As the NOAEC for both studies was based on no observed adverse effects at the highest dose tested, and lanthanum carbonate is believed to be better comparable with regard to its bioavailability to lanthanum oxide than lanthanum trichloride (because of its lower water solubility compared to the chloride, but still higher than the oxide), it seems reasonable to use in this case the higher value from the 90-day rat study.

Conclusion on classification

Lanthanum oxide is not classified for environmental effects as it did not show any toxicity in acute aquatic studies and a 21 -day daphnia reproduction study at the saturation concentration and a loading rate of 100 mg/L. As a metal compound lanthanum oxide is not considered biodegradable, but as it does not excert toxicity in long term aquatic studies and does not biomagnify in the aquatic food chain, no classification for possible long-term effects in the aquatic environment is warranted.