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Description of key information

Key value for chemical safety assessment

Additional information

No experimental studies of dineodymium tricarbonate with animals or humans on absorption, metabolism, distribution, or elimination in mammals were available. However, information is available from existing toxicology studies to infer potential toxicokinetic properties. In toxicity testing, the test material is provided as a solid powder which is made into an aqueous suspension using carboxymethylcellulose or propylene glycol.  

Systemic availability of dineodymium tricarbonate depends on its ability to be absorbed across body surfaces. Factors that affect this process include water solubility, lipophilicity (measured by the partition coefficient, Kow), degree of ionization (the dissociation constant, pKa), and molecular size. Based on its formula, the substance is almost 500 g/mol and sparingly soluble in water. No dissociation constant or log Kow was available for this substance. 

ORAL EXPOSURE

Oral toxicological studies suggest that dineodymium tricarbonate is likely to be minimally absorbed following oral exposures. The acute oral LD50 was estimated to be greater than 2000 mg/kg bw in a GLP-compliant OECD 420 oral gavage study, with no clinical signs and no effect on body weight observed. In a GLP-compliant OECD 422 repeat-dose/reproductive study with a structurally similar compound, dicerium tricarbonate, changes in the stomach lining, including hyperplasia, indicating irritation were noted. Systemic toxicity was limited to blood biochemical changes and decreased white blood cell counts noted at the highest dosage only (1000 mg/kg bw/day), and on this basis a NOAEL for systemic toxicity was set at 450 mg/kg bw/day. 

DERMAL EXPOSURE

No studies investigating the absorption through the skin were available; but some toxicokinetic information can be inferred from the toxicological studies.  In a GLP-compliant OECD 429 in vivo local lymph node assay in mice, dermal administration of up to 25% w/w (the highest technically achievable concentration) was used to assess sensitisation; no effects were identified supporting the lack of absorption through the skin. The test substance is inorganic in nature and is not expected to be lipophilic and based on its formula, the molecular size is on the large size which may also preclude dermal absorption. 

INHALATION EXPOSURE

In an acute inhalation study, performed with a structurally related compound, lanthanum carbonate-octahydrate, nose-only exposure for 4 hours at a concentration as high as 5928 mg/m3 air did not cause any mortality. Limited clinical signs were observed in few animals during exposure and up to the day following exposure. Macroscopic examination at termination, 14 days after the 4-hrs exposure, evidenced whitish, highly viscous deposits into the lungs of some exposed animals, when their lungs were cut, thus demonstrating that the substance had reached the alveoli, but was neither toxic nor extensively absorbed.

CONCLUSION

In the absence of significant absorption via any exposure route it is anticipated that the substance will not be distributed or metabolised by the body. As such it is reasonable to assume that the substance will be excreted via urine or faeces following exposure.