BIOLOGICAL TRANSFER OF PLUTONIUM-238 VIA IN VIVO LABELED MILK William W. Sutton National Environmental Research Center, Las Vegas* Despite the fact that the biological transport of plutonium has been studied for many years, quantitative values for its transfer to milk, its distribution in tissues (both edible and nonedible), and its subsequent uptake by suckling calves or humans have not been established. farm, The basis for this study, currently in progress at the NTS is that people especially children consume large quantities of dairy products and beef (muscle and organs) so that any evaluation of radiological hazards associated with a plutonium-contaminated country- side must consider the biological availability of in vivo plutoniumlabeled food (milk and meat). During the range-finding portion of this study, a lactating dairy cow was given a single 83-mCi intravenous dose of plutonium-238 citrate. Milk, blood, urine, and feces were collected for analysis until the cow was sacrificed three days after dosing. It was determined that this amount of plutonium was too high for the objectives of this study. Another lactating cow was then given an acute 10-mCi plutonium-238 citrate intravenous injection. As before, collections of milk, blood, urine, and feces were taken for analysis. In both cases, preliminary results indicate that slightly less than 1% of the original dose had been secreted in the milk 72 hrs after injection. The second animal has subsequently been given three additional intravenous doses (10 mCi per day for three consecutive days). Milk collections are being placed in suitable buckets and fed to two calves at a rate *See footnote, p. 35. o1