Swan thyroid glands and river algae as indicators of iodine-125 and iodine-131 in the River Trent and its tributaries.

ABSTRACT

Some mute swans have been found to have higher levels of radio-iodine in their thyroids than farm and wildlife animals. In the East Midlands of the U.K., elevated levels were confined to swans inhabiting major rivers like the Trent and Soar where the highest values occurred in thyroids collected downstream from sewage and water reclamation works. Comparing the concentrations of 125I and 131I in blanket weed, which is a food source of the swan, and river water samples collected from above, below and in such effluents, showed that radio-iodine enters the river via these routes. The environmental pathway is sewage effluent--(water reclamation)--river water--river weed--swan. The radioactivity originates from the widespread use of radio-iodine in hospitals and analytical laboratories where much of the liquid and soluble waste is discarded into the sewage drain system. With a simple counting assembly consisting of a heavily shielded thin NaI(Tl) crystal detector attached to a 2-channel scaler-timer it was possible to check large numbers of swan thyroid glands. Although relatively high count rates were frequently obtained the levels of radio-iodine in thyroids were too low to affect the health and well-being of the swan.