In recent years, the use of both nano- and micro-sized
lanthanum has been increasing in the production of optical glasses, batteries,
alloys, etc. However, a hazard assessment has not been performed to determine the degree of toxicity of
lanthanum. Therefore, the purpose of this study was to identify the toxicity of both nano- and micro-sized
lanthanum oxide in cultured cells and rats. After identifying the size and the morphology of
lanthanum oxides, the toxicity of two different sized
lanthanum oxides was compared in cultured RAW264.7 cells and A549 cells. The toxicity of the
lanthanum oxides was also analyzed using rats. The half maximal inhibitory concentrations of micro-La2O3 in the RAW264.7 cells, with and without sonication, were 17.3 and 12.7 times higher than those of nano-La2O3, respectively. Similar to the RAW264.7 cells, the toxicity of nano-La2O3 was stronger than that of micro-La2O3 in the A549 cells. We found that nano-La2O3 was absorbed in the lungs more and was eliminated more slowly than micro-La2O3. At a dosage that did not affect the
body weight, numbers of leukocytes, and concentrations of
lactate dehydrogenase and
albumin in the bronchoalveolar lavage (BAL) fluids, the weight of the lungs increased. Inflammatory effects on BAL decreased over time, but lung weight increased and the proteinosis of the lung became severe over time. The effects of particle size on the toxicity of
lanthanum oxides in rats were less than in the cultured cells. In conclusion, smaller
lanthanum oxides were more toxic in the cultured cells, and sonication decreased their size and increased their toxicity. The smaller-sized
lanthanum was absorbed more into the lungs and caused more toxicity in the lungs. The histopathological symptoms caused by
lanthanum oxide in the lungs did not go away and continued to worsen until 13 weeks after the initial exposure.