Determination of plutonium activity concentrations and 240Pu/239Pu atom ratios in Brown Algae (Fucus distichus) collected from Amchitka Island, Alaska

Plutonium-239 (239Pu) and plutonium-240 (240Pu) activity concentrations and 240Pu/239Pu atom ratios are reported for Brown Algae (Fucus distichus) collected from the littoral zone of Amchitka Island (Alaska), and at a control site at Unalaska, Alaska. The average 240Pu/239Pu atom ratio observed in dried F. distichus collected from Amchitka Island was 0.227 ± 0.007 (N = 5) and compares with the expected 240Pu/239Pu atom ratio in integrated worldwide fallout deposition in the Northern Hemisphere of 0.1805 ± 0.0057. In the absence of any evidence of a local source of plutonium containing an elevated 240Pu/239Pu isotopic signature, the characteristically high 240Pu/239Pu content of F. distichus supports the view of the existence of a discernible, basin-wide non-fallout source of plutonium entering the subarctic Pacific.