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）.