- The uptake, retention, and distribution of ⁶⁰Co, ⁶⁵Zn, ⁸⁵ Sr, and ¹³¹I was examined in the Rough-Skinned Newt (Taricha granulosa). Each of these radionuclides is a possible contaminant of the freshwater environment and, thus, is of importance in radioecology. The newts were maintained singly at 10° C in an unfed condition. An Armac liquid scintillation detector was used for determination of whole-body radioactivity and tissue samples were assayed in a 3" x 3" NaI(Tl) well crystal. The counting error did not exceed the 1% level. The uptake of ⁶⁰Co, ⁶⁵Zn, and ⁸⁵Sr from water and whole-body retention after this chronic exposure was compared to retention patterns obtained after a single injection (I. P.). These retention curves showed two components, a short-lived component and a long term component. The biological half-lives of the long term components after chronic and acute administration were 127 and 114 days for ⁶⁰Co, 1233 and 1260 days for ⁶⁵Zn, and 136 and 131 days for ⁸⁵Sr, respectively. The whole-body retention of ¹³¹I was followed after acute administration only A two component curve was seen with the fast component having a biological half-life of 2.05 days and containing 74% of the initial dose. The long term component had a biological half-life of 210 days. Effective half-lives for the long term components of the ⁶⁰Co, ⁶⁵Zn, ⁸⁵Sr, and ¹³¹I retention curves were calculated using the above biological half-lives. The pattern of distribution of the four radionuclides in the tissues of the newt was determined over a 100 day period for ⁶⁰Co, ⁶⁵Zn, and ⁸⁵Sr, but only over 27 days for ¹³¹I. Fourteen tissues were assayed for activity after a single injection (I. P. ). They included blood, skin, thyroid, spleen, liver, stomach, intestine, lung, heart, testes, kidneys, bone, eyes, and muscle. The kidneys accumulated the major concentration of ⁶⁰Co and the eyes concentrated radiozinc to a greater extent than the other tissues. Bone was the site of the highest concentration of ⁸⁵Sr, while the thyroid concentrated ¹³¹I more than all other tissues combined. With the exception of ¹³¹I, the relatively long effective half-lives indicated that the radioactivity would be found in an exposed amphibian population for a considerable time period. Predators of these amphibians could then acquire radioactivity long after the original contamination of the freshwater system. Radioiodine, due to its short effective half-life, would become a hazard only in areas of excessive contamination or where a short food chain is involved.