TRANSURANIC RADIONUCLIDES IN ENEWETAK LAGOON 585 



82 + 6 



Fig. 3 Activities of ^^'Am (millicuries per square kilometer) associated with the 

 sediment components in the top 2.5-cm layer of Enewetak lagoon. 



radioactivity might have escaped detection. The areal distributions are based on available 

 data from the samples that were collected and analyzed. 



The transuranics are distributed nonuniformly over the lagoon floor. Highest surface 

 concentrations are associated with the sediments near, but not necessarily adjacent to, the 

 locations of larger or more numerous nuclear tests. Highest plutonium concentrations are 

 associated with the sediments from the northwest quadrant in a north- and south-oriented 

 elliptical area that is roughly 2 to 3 km east of the islands of Alice and Belle and several 

 kilometers southwest of Mike and Koa craters. A second region of relatively high 

 concentration is in sediments off the shore of Yvonne Island. The activity in this region is 

 lower than that in sediments in the northwest. Most of the transuranic inventory in the 

 surface sediments can be separated roughly from the lesser contaminated deposits by a 

 line extending from the Southwest Passage to the island of Tom (Munjor), which is south 

 of Yvonne on the eastern reef. The surface 2 39+2 40p^ concentrations north of this line 

 range between 2 and 170 pCi/g (dry weight); those south of this line are less than 2 pCi/g. 

 All surface-sediment samples obtained during and since 1972 contained ^^^ ^'*°Pu. The 

 inventory (mCi/km^) in only the top 2.5-cm layer of sediment exceeds the activity 

 deposited to the earth's surface as worldwide fallout in any latitude band in the northern 

 or southern hemisphere (Hardy, Krey, and Volchok, 1973). 



