Subchronic Oral Toxicity Evaluation of Lanthanum: A 90-day, Repeated Dose Study in Rats.

Objective: The present study was undertaken to evaluate the subchronic toxicity of lanthanum and to determine the no observed adverse effect level (NOAEL), which is a critical factor in the establishment of an acceptable dietary intake (ADI).

Methods: In accordance with the Organization for Economic Co-operation and Development (OECD) testing guidelines, lanthanum nitrate was administered once daily by gavage to Sprague-Dawley (SD) rats at dose levels of 0, 1.5, 6.0, 24.0, and 144.0 mg/kg body weight (BW) per day for 90 days, followed by a recovery period of 4 weeks in the 144.0 mg/kg BW per day and normal control groups. Outcome parameters were mortality, clinical symptoms, body and organ weights, serum chemistry, and food consumption, as well as ophthalmic, urinary, hematologic, and histopathologic indicators. The benchmark dose (BMD) approach was applied to estimate a point of departure for the hazard risk assessment of lanthanum.

Results: Significant decreases were found in the 144.0 mg/kg BW group in the growth index, including body weight, organ weights, and food consumption. This study suggests that the NOAEL of lanthanum nitrate is 24.0 mg/kg BW per day. Importantly, the 95% lower confidence value of the benchmark dose (BMDL) was estimated as 9.4 mg/kg BW per day in females and 19.3 mg/kg BW per day in males.

Conclusion: The present subchronic oral exposure toxicity study may provide scientific data for the risk assessment of lanthanum and other rare earth elements (REEs).