Dicerium tricarbonate

Bioaccumulation: aquatic / sediment

Description of key information

Dicerium tricarbonate has no potential for bioaccumulation.

Additional information

The Cerium anomaly, ingeochemistry, is the phenomenon whereby Cerium(Ce) concentration is either depleted or enriched in a rock relative to the other rare earth elements(REEs). A Ce anomaly is said to be "negative" if Ce is depleted relative to the other Rare Earth Elements and is said to be "positive" if Ce is enriched relative to the other Rare Earth Elements.

Geochemistry analysis and bibliography explains a well know specificity of the cerium in the aquatic environmental compartment: the cerium anomaly (Nozaki, 2003 ;Sholkovitz, 1995 ). We speak about a positive anomaly when the cerium concentration is enriched relative to the other rare earth and a negative anomaly when the cerium concentration is depleted.

More recently, Pouret O.(2007 and 2008) studied this phenomenon in more details in order to explain the comportment of the cerium carbonate in water, pore water and sediment. The speciation of the cerium was determined, in this research work, by Inductive Coupled Plasma Mass Spectrometry, after ultrafiltration process, in order to separate the sediment part and the pore water part.

 

According to the bibliography, the negative anomaly especially takes place in oceanic and river water. In fact, Nozaki (2003) explains that: “Two elements, Ce and Eu can take the other oxidation states. Although Ce is generally well accommodated within the strictly trivalent lanthanide series in igneous rocks, oxidation reaction of Ce3+ to Ce4+ proceeds in oxygenated aqueous systems. In seawater, the resulting Ce4+ hydrolyzes readily and tends to be removed by scavenging. For this reason, seawater is typically depleted in Ce relative to that expected from neighboring La and Pr, whereas Ce is often enriched in some authigenic minerals such as manganese nodules and phosphorites.”

In this study (see key study record under the IUCLID-Section 5.6), scored reliability 2, Pouret O. (2008) has shown and confirmed that the positive anomaly takes place in organic phase, such like sediment, which composition is rich in humic acid composition.

 

As a conclusion of this study, which was conducted on 14 naturally rare earth, Pouret O. explained:” The role of HA and carbonate competition on Ce oxidation and Ce anomaly development was examined by considering the REE patterns of the organic and inorganic fractions as a function of pH. A negative Ce anomaly is developed in the REE fraction bound to carbonate at pH above 8.2, 8.6 and 8.7 at alkalinities of 10-3 mol L-1, 5 x 10-3 mol L-1 and 10-2 mol L-1, respectively, whereas a positive Ce anomaly is developed in the organic fraction (i.e., >5 kDa). Partitioning is observed between the organic phase (LnHA) and inorganic phases (Ln-carbonate). In the inorganic phase, Rare Earth Element patterns display Heavy Rare Earth Element enrichment typical of seawater.These experiments shed more light, not only on a new way to develop a Ce anomaly, but also on the understanding of cerium anomaly cycle in natural waters at alkaline pH. Indeed, these results suggest a new mechanism for cerium anomaly development. In the presence of carbonate, cerium is readily oxidized to Ce(IV), which is easily removed from solution by preferential adsorption to HA. Humic substances take up Ce(IV) from the "truly" dissolved part of solution (i.e., <5 kDa), and a negative cerium anomaly thus develops in the inorganic fraction. A complementary positive Ce anomaly develops in the organic fraction. The preferential Ce(IV) sorption is masked.”

 

To summarize, this study clearly demonstrates that the cerium, which is depleted in the water part, is mainly presented under a carbonate form whereas the cerium carbonate is removed from the water solution by an adsorption to the humic acid but under a Cerium IV oxidation degree.

These observations of the Cerium anomaly compared to the other rare earth are well demonstrated by the enclosed spectrum provided by the author. 

 

These anomalies of the cerium were also presented by Moermond et al.(2001) (remiability scored 2), who analysed the distribution, speciation and bioavailability of lanthanides in the Rhin-Meuse Estuary. The study also focused on the calculation and comparison of the biota sediment accumulation factor (BSAF) onCorophium volutatorunder field and laboratory conditions.

 

The author demonstrates that the grade of accumulation on the sediment biota for the cerium is:

- BSAF field = 0.078 kg dry weight/kg sediment and

- BSAF laboratory = 0.396 kg dry weight/kg sediment

 

The BCF was evaluated, divided the biota concentration (amphipods) by the concentration in pore and surface water, on six site of the Rhin-Meuse estuary.

The results are presented in the publication and show that the calculated BCF for cerium is never above 137 L/Kg for each sample (calculation obtained from graphics). This confirms that the cerium is not concentrated in the biota.

 

In one hand, these results show than even if, according to the cerium anomaly largely explained in the literature, the cerium is more present in the sediment part, there is no bioaccumulation in the biota.

In the other hand, the study shows that the BSAF determination in laboratory was significantly higher than in field for all the Rare Earth tested. The author suggests that it should be due to an adaptation of the invertebrate but no scientific prove are given.

All these studies clearly demonstrate the influence of the pH and alkalinity in the speciation of the rare earth in the sediment and water phase but also demonstrate that there is no accumulation in the biota of the sediment phase, which is the environmental compartment where the cerium is concentrated.

As described in the "short description of key information" part, several studies have shown that there is not bioaccumulation of cerium salt in fish.

 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 dicerium tricarbonate. 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 auratusfor 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.skeletons, 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 carpioranged 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. Dicerium tricarbonate shows a low water solubility (< 3.95 mg/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 poorly soluble form of cerium (i.e. carbonate) should not show any potential for bioaccumulation, as the most soluble ones (i.e.chloride and nitrate).

The detailed results already published, which clearly state on the transformation of the cerium carbonate in the environment, and as there is no accumulation of cerium in sediment biota nor in fish there is no scientific justification to propose other test on the bioaccumulation in sediment.