ABSTRACT
Strontium salts are virtually nontoxic orally, and no reports of adverse effects from industrial use of Sr are available. Acute inhalation toxicity for strontium has been observed in experimental animals, causing respiratory failure. In biological systems an interdependence between Sr2 and Ca2 exists because the two ions are similarly metabolized (1,2). In fact, strontium metabolism is not directly regulated by levels of the element in the body but is determined by homeostatically controlled calcium levels. There is evidence that Sr is essential for the growth of animals and especially for the calcification of bones and teeth (3). A functional association of strontium with calcium was observed to occur in cell differentiation processes: the presence of strontium-induced terminal differentiation of cultured mouse keratinocytes in low-calcium growth media; however, higher doses of calcium were required to produce the same effects when strontium was absent in the media (4). While chemically strontium is virtually nontoxic, it is nevertheless of major toxicological interest due to the abundance of its radionuclides, primarily of 90Sr, introduced into the biosphere as a result of nuclear detonations and other uses of nuclear energy (5). Its radioactive isotopes released into the environment become incorporated into the food chain and hence accumulate in the body tissues of humans. Adding to the hazard is long-term retention in skeletal tissues of 90Sr, where it is particularly resistant to removal by chelation. The nuclide has a biological half-life (the retention half-time corrected for physical decay) of 28 years, and lodged in bone it destroys nearby capillaries, decreasing local blood flow, and also can result in an increased incidence of neoplasia due to radiation. Among the most frequently observed neoplasms is epidermoid carcinoma (6). Metabolic studies have been conducted in great detail on a number of animal species to clarify the potential adverse effects of food chain contamination with strontium nuclides (7).
