Technetium absorption and turnover in monogastric and polygastric animals

Technetium (Tc) released into the environment can reach animals in various chemical forms: as pertechnetate (TcO-4) in drinking water or deposited on the surface of vegetables and forage plants, or as Tc bioincorporated into plants and associated with various plant constituents. In addition to being influenced by chemical speciation in the diet, absorption, metabolism, and retention of Tc in animals are modified by the treatment that the alimentary bolus undergoes during its passage through the gastrointestinal tract. This behavior differs markedly between polygastric and monogastric animals. We have, therefore, studied the fate of 99mTc given in the diet either as TcO-4 or bioincorporated into maize in rats (as an example of a monogastric animal) and in sheep (as an example of a polygastric animal). Urine and feces were collected and assayed for Tc activity by gamma spectrometry. Animals were sacrificed at different times after contamination, and the Tc content of tissues was determined. The pattern of absorption, excretion and, to a certain degree, of organ distribution and retention depended on animal species and species of Tc administered. Excretion was by feces and urine, and several metabolic components could be discerned. A component of very short half-time in urine suggests that newly absorbed Tc is more readily excreted than that already bound by tissues. The highest tissue concentrations were found in the thyroid. Retention of Tc was, however, most pronounced in bone and skin. Hair contains considerable amounts of Tc and may serve as a bioindicator of Tc contamination.