RESUMEN
Thorium has gained notoriety in recent years, as a potential source of nuclear energy, substituting uranium in power plants. Monazite is an important source of thorium, as well of uranium and rare earths elements. Workers involved in the extraction and manipulation of this mineral are occupationally exposed to a range of metal mixtures containing thorium and to ionizing radiation. As an osteotropic substance, thorium is mostly deposited in bone tissue and may interfere in cellular radiosensitivity. A human osteoblast cell line was used to evaluate the effects of thorium (Th), cerium (Ce) and lanthanum (La) on cell radiosensivity, using proliferation as indicator. Assays were performed using cell cultures exposed to metals alone and metals combined with ionizing radiation. No stimulus of proliferation was observed when samples were exposed to metals or radiation alone. On the other hand, the metals were able to influence cell radiosensivity, in a concentration-dependent manner when metals and radiation were applied simultaneously. Samples irradiated and exposed to metals combinations revealed an interaction between them in all the tested arrangements (Th-Ce, Th-La, Th-Ce-La). All interactions proved to be of the antagonist type relative to the proliferation indicator, with a higher degree seen for the Th-Ce association. Such results showed the possibility that metal mixtures together with radiation may produce combined effects on osteoblasts, through modifications on the degree of radiosensivity. The results indicate the possibility of an enhancement in occupational risk for workers that manipulate monazite byproducts. Thus, the development of risk assessment models that include the evaluation of mixtures and their cytotoxic and radiotoxic effects on tissues and organs must be highlighted.