Lanthanum trihydroxide

Endpoint summary

Description of key information

For the purposes of human risk assessment, oral absorption of the substance is estimated at 50%, inhalation absorption is estimated at 100% and dermal absorption is estimated at 25%.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

50

Absorption rate - dermal (%):

25

Absorption rate - inhalation (%):

100

Additional information

Introduction

The substance is a yellow powder.

No experimental studies of lanthanum trihydroxide with animals or humans on absorption, metabolism, distribution, or elimination in mammals are available. However, information is available from existing toxicology studies from which limited inferal of potential toxicokinetic properties might be made.

Systemic availability of lanthanum trihydroxide 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. The substance has a molecular weight of 189.9 g/mol and is virtually insoluble in water (one source stating 20 µg/L). Rare earth oxides and hydroxides are known to become more soluble in mineral acids however. No dissociation constant or log Kow is available for this substance. Kow are not required for inorganic substances.

Absorption

Oral absorption

The acute oral LD50 was estimated to be greater than 2000 mg/kg bw in an OECD 420 acute oral study, with no clinical signs that could be related to treatment and no effect on body weight observed. In addition, no gross abnormalities that could be related to treatment were observed at necropsy. Nothing can be inferred about the nature of oral absorption from this study.

In an OECD 408 repeat-dose dietary study, treatment with a read-across substance (up to 741 mg/kg bw/day in males and 1126 mg/kg bw/day in females) no adverse effects were observed.

Nothing can be inferred about the nature of oral absorption from this study.

Because of the insolubility of the material in water absorption via the oral route is unlikely, although in the absence of other information, the unquantified effect on solubility of stomach acid, and for the purposes of human DNEL setting, 50% bioavailability is assumed.

Dermal absorption

The acute dermal LD50 of the substance was estimated to be greater than 2000 mg/kg bw in a GLP-compliant OECD 402 study, with no treatment related clinical signs or effects on body weight observed. No gross abnormalities were observed at necropsy.

Skin irritation and sensitisation studies also gave no signs that the test material reacted chemically with living layers of the skin.

Nothing can be inferred about the dermal penetration properties of the test material from these studies.

For the purposes of DNEL setting however, estimation of mammalian dermal absorption is made in accordance with principles adopted EFSA guidance on estimating dermal absorption of pesticide active substances (EFSA, 2012). On this basis, dermal absorption is estimated at 25% for undiluted material.

Inhalation absorption

The substance is a hygroscopic, lumpy solid and as such it was not possible to conduct an acute inhalation study. Given the physical properties of the substance inhalation exposure is unlikely.

In the absence of any quantitative data, absorption of material that makes it into the alveoli is considered to be 100%.

Distribution, metabolism, excretion

No information is available to describe the distribution, metabolism of the material. Given there is unlikely to be any oral absorption, ingested material is likely to pass through the GIT and merger in the faeces.

Conclusion

For the purposes of human risk assessment oral absorption of the substance is estimated at 50%, inhalation absorption is estimated at 100% and dermal absorption is estimated at 25%.