Biomonitoring of Pu isotopes in liver of North Pacific giant octopus (Enteroctopus dofleini) collected off the Rokkasho Nuclear Fuel Reprocessing Plant, western North Pacific margin

Concentrations of Pu239+240 and Pu-240Pu/239 atom ratios were determined in liver samples of North Pacific giant octopus (Enteroctopus dofleini) collected off the Rokkasho Nuclear Fuel Reprocessing Plant (RNFRP) to understand the bioaccumulation of Pu in the octopus liver, to provide Pu data before full commercial operation of the reprocessing plant, and to identify the sources of Pu isotopes in the studied liver samples. Mean Pu239+240 concentration was 6.3 +/- 3.1 mBq/kg-wet, which was within the previously reported concentration ranges in liver of the Japanese common squid and in hepatopancreas of red queen and snow crabs. The Pu-240Pu/239 atom ratios ranged from 0.223 to 0.252 with a mean ratio of 0.234 +/- 0.009, which was noticeably greater than the mean global fallout ratio of-0.18. These ratios reflected a mixture of global fallout Pu from atmospheric nuclear weapons testing and close-in fallout Pu from the Pacific Proving Grounds (PPG). The relative percentage of the PPG close-in fallout Pu to global fallout was calculated to be 39.6 +/- 6.7%. The liver of the NPG octopus is an excellent bioindicator for biomonitoring of Pu pollution. Data on Pu239+240 concentrations and Pu-240Pu/239 atom ratios in liver of the NPG octopus collected in the vicinity of the RNFRP will provide powerful keys for continuous biomonitoring of Pu pollution and for distinguishing the potential sources of Pu after the plant begins full commercial operation.

Automated summary

The concentrations of Pu239+240 and the Pu-240Pu/239 atom ratio were analyzed in liver samples of the North Pacific giant octopus collected near the Rokkasho Nuclear Fuel Reprocessing Plant. The results showed that the Pu concentrations were similar to those reported in other marine organisms, while the Pu-240Pu/239 atom ratio was higher than the global fallout ratio, indicating the presence of Pu from atmospheric nuclear weapons testing and the Pacific Proving Grounds. The liver of the North Pacific giant octopus is a valuable bioindicator for monitoring Pu pollution.