Lanthanum oxide

Bioaccumulation: aquatic / sediment

Description of key information

Limited Laboratory studies of bioconcentration of soluble lanthanum compounds in fish did not show a high bioconcentration. Solube lanthanum compounds were reproted to bioconcentrate in aquatic algae, zooplankton and some invertebrates to a varying extend. Lanthanum did not show trophic biomagnification in a pelagic foodweb. These findings were also supported by a mesocosm study. Overall it can be concluded that lanthanum does not biomagnify in the food chain and does not lead to a concern with regard to secondary poisoning. Lanthanum oxide, because of its low water solubility, in particular is assumed to have a low bioavailability even for algae and zooplankton that were shown to accumulate soluble lanthanum to a certain extend. Thus a bioaccumulation is not to be expected.

Additional information

No classical bioaccumulation study according to OECD guideline 305 is available for Lanthanum oxide.

According to “Guidance on information requirements and chemical safety assessment Appendix R.7.13-2: Environmental risk assessment for metals and metal compounds” the determination for bioaccumulation potential for naturally occurring substances such as metals, is more complex and most concepts and tools to assess the bioaccumulation were inadequate for the assessment of metals since the methods were originally developed on limited results obtained for neutral lipophilic organic substances that have shown that their potential to bioaccumulate and/or to biomagnify is directly related to the inherent properties of the substance.

Tu et al (1994) investigated the bioconcentration of lanthanum nitrate in Cyprinus carpio in a semistatic experiment. Control animals were used for analysis of the background value in carp. Bioaccumulation values referred to the difference between the background concentration in control fish tissue and the concentration in tissues derived from exposed fish. The maximum bioconcentration factor (BCFmax) was calculated by dividing the maximum concentration of the test substance in certain tissue of carp by the nominal concentration of the same element in the test water. The highest BCF was 91 (recalculated from tabulated data in the study) in internal organs and lower values for gills, skeleton and muscle that were in the range of 5.6 to 18.

 Sun et al. (1996) investigated the bioaccumulation of mixed REE nitrate hydrates (amongst others Lanthanum) in Cyprinus carpio. Large variations of BCFs (calculated as the concentration of test substance in fish tissue (mg/kg) divided by the nominal concentration of test substance in the test) were observed for different tissues, the highest BCF was found in the internal organs with a range of 45.2- 828. The values for internal organs vary a lot and the high values at 29 and 43 d seem to be rather outliers and perhaps related to the tissue processing and analytical method. Abnormally high values were also found for the other elements investigated at the same time points which can hint to a processing or dilution error.

Furthermore if gut content was included in the data for internal organs, concentrations measured in the gastrointestinal tract are not considered representative of bioacumulation as they reflect transit of unabsorbed substance.

The maximum BCF values should therefore be treated with caution. They are also not consistent with the values derived by Tu et al. in a very similar experiment.

 distinct lower BCFs were stated in the gills, skeleton and muscle which were in the range of 0.44 – 13.8.

For the lanthanum metal ion several field and laboratory studies are available that determined the concentration as lanthanum in biota of different trophic levels including algae, invertebrates, fish and birds. From these studies several bioconcentration factors were derived. In addition the trophic magnification in a pelagic food web covering 15 species was investigated and a mesocosm study with four trophic levels, that however suffers from limited reporting was reported in the literature

  

Sneller et al. (2000) reported BCFs for different species, sampled from 6 locations in the dutch Rhine estuary. The range of the stated BCF for bivalves, worms and crustaceans were 15000 – 50000, 8000 - 120000 and 10000 – 40000, respectively. Sneller et al., 2000 concluded, however that the reported BCF values do not indicate that rare earth elements are highly bioavailable for animals and that biomagnification is unlikely.

 

Stronkhorst and Yland (1998) and Sneller et al. (2000) compared the bioaccumulation in Corophium volutator (amphipoda) in a laboratory and a field study. The calculated BCF in the laboratory examination was 22387 corresponding to the pore water and 107152 corresponding to the surface water, the BCF in the field study was 28840. The BCF related to pore water was about a factor of 5 lower than the BCF related to the surface water. The BCF (related to pore water) calculated for the field was higher than the BCF (related to the pore water) calculated for the laboratory experiments. According to the authors this can be attributed to the fact, that the pore water concentration in the laboratory experiments was increased by the stirred sediment. The BSAF (biota sediment accumulation factor) was low (2.57), induced by the high adsorption of Lanthanum to the sediment.

 

The low BSAF for Corophium volutator was confirmed by Moermond et al. (2001), who stated a BSAF of 0.079 in a field study and 0.386 in a laboratory study.

A further field study was conducted by Weltje et al. (2002), who determined the BCF in snails and bivalves at five locations in the Netherlands. The calculated range for the BCF was 9000 – 250000 and 14000 – 30000 for snails and bivalves (on a dry weight basis), respectively. Furthermore the BCF in two aquatic plants (based on dry weight) was investigated: The range of the BCF for Potamogeton pectinatus was 6000 - 300000 based on the concentration in surface water and 2000 - 300000 based on the concentration in pore water. For Lemna minor a range of approx. 10000 - 20000 was stated based on the concentration in surface water.

In addition Campbell et al. (2005) analyzed lanthanum, amongst 21 other metal compounds, in a pelagic arctic food web to investigate trophic magnification. The trophic level of the respective organism was determined using stable nitrogen and carbon isotopes (15-N and 13-C. The slope of the metal ion level against trophic levels as determined by delta-15-N is defined as trophic magnification factor. Metal and 15-N isotope levels were determined in 15 species of Northwater Polynya Baffin Bay food web.

Lanthanum was found at less than 0.01 micro-g/g or below detection limit in seals, fish and birds, but at slightly higher concentrations in zooplankton. The regression analysis for the NOW food web using whole invertebrates, arctic cods and vertebrate muscle data did not show any significant slope indicating that lanthanum did not biomagnify in this food web. From the results it can be concluded that lanthanum is concentrated to a certain extend in algae and zooplankton, but concentration decreased in higher trophic levels.

This finding was also corroborated by a 16-d mesocosm study with freshwater and sediment of a Chinese lake, duckweed, daphnia magna, shellfish and goldfish by Yang et al. 1999.. After 12 to 24 h the majority of the lanthanum (added as soluble lanthanum dinitrate in a mixture of other rare earth salts) was bound to sediment. (90.95%) while 8.245 was reported to stay in water and 0.81 % taken up in biota. At the end of the experiment (d 16) the bioconcentration factor was determined for the different species. Due to the non-detectable concentration in goldfish and daphnids, no BCF was determined for these species. For Duckweed a BCF of 138.1 and for shellfish of 2.11 was reported. The highest uptake was observed in the duckweed. 

The BCFs, calculated in field studies, showed wide variations of up to three orders of magnitude. This can be attributed to variations in abiotic parameters of different sampling locations, variations in bioavailabilty, as well as to different affinities among organisms to lanthanum and to difficulties in analytical determination of free lanthanum. Fish, which are only tested in the laboratory study by Sun et al. (1996) showed the lowest bioaccumulation potential, compared to crustaceans, snails, bivalves, worms and aquatic plants. A pelagic food web study confirmed that lanthanum does not biomagnify in the food chain.

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It is known that organisms are able to modulate both accumulation and potential toxic impact of internal concentrations of metals through (1) active regulation, (2) storage, or (3) a combination of active regulation and storage over a wide range of environmental exposure conditions. Although these homeostatic control mechanisms have evolved largely for essential metals, it should be noted that non-essential metals are also often regulated to varying degrees because the mechanisms for regulating essential metals are not entirely metal-specific. Chassard-Bouchard and Hallégot (1984) examined the Lanthanum content in Mytilus edulis collected from French coastal waters of the Channel, Atlantic Ocean and. 139La+ was detected within lysosomes of digestive gland, labial palp and gill epithelium, macrophage hemocytes and chitinous tissue. Furthermore, Lanthanum was always associated with high phosphorus contents in the lysosomes. Thus, Lanthanum which exists in sea water at trace level is taken up by the Mussel, via gill and digestive tractus, in a soluble form and then concentrated in the form of an insoluble phosphate in the storage organelles. This process can be assessed as detoxification mechanism, comparable to the process observed after oral uptake of Lanthanum in vertebrates.

Chassard-Bouchard, C. and Hallégot P. (1884): Bioaccumulation of lanthanum by the mussels Mytilus edulis collected from French coasts. Microanalysis by X-ray spectrography and secondary ion emission. C R Acad Sci III. 298(20): 567 -572

Overall it can be concluded that lanthanum does not biomagnify in the food chain and does not lead to a concern with regard to secondary poisoning. Lanthanum oxide, because of its low water solubility, in particular is assumed to have a low bioavailability even for algae and zooplankton that were shown to accumulate soluble lanthanum to a certain extend. Thus a bioaccumulation is not to be expected.