Findings of the first comprehensive radiological monitoring program of the Republic of the Marshall Islands.

摘要

The Marshall Islands was the primary site of the United States atomic weapons testing program in the Pacific. From 1946 through 1958, 66 atomic weapons were detonated in the island country. For several decades, monitoring was conducted by the U.S. Department of Energy (or its predecessor agencies) on the test site atolls and neighboring atolls. However, 70% of the land area of the over 1,200 islands in the Marshall Islands was never systematically monitored prior to 1990. For the 5-y period from 1990 through 1994, the Government of the Republic of the Marshall Islands undertook an independent program to assess the radiological conditions throughout its 29 atolls. The scientific work was performed under the auspices of the Section 177 Agreement of the Compact of Free Association, U.S. public law 99-239, signed in 1986 by President Ronald Reagan. Although the total land area of the nations is a scant 180 km2, the islands are distributed over 6 x 10(5) km2 of ocean. Consequently, logistics and instrumentation were main considerations, in addition to cultural and language issues. The core of the monitoring program was in-situ gamma spectrometry measurements made on more than 400 islands. Native foods including coconuts and other tropical fruits were sampled as well as more than 200 soil profiles and more than 800 surface soil samples. The fruits, soil profiles and surface soil samples have been analyzed for all gamma emitters with an emphasis on determining concentrations of 137Cs; the surface soil samples were also analyzed for 239+240Pu. All measurements were conducted in a radiological laboratory built in the capital city of the Marshall Islands specifically for the purposes of this study. The program was extensively assisted in the field and in the laboratory by Marshallese workers. The interpretation of environmental radiation data in the Marshall Islands required thoughtful analysis because the atolls lie along a latitude and precipitation gradient that effected the deposition of local and global fallout. The objective of this paper is to report findings for all atolls of the Marshall Islands on the 137Cs areal inventory (Bq m(-2)) and the external effective dose-rate (mSv y(-1)), the projected internal effective dose-rate (mSv y(-1)) from an assumed diet model, and surface soil concentrations of 239,240Pu (Bq kg(-1)) for selected northern atolls. Interpretation is also provided on the degree of contamination above global fallout levels. This report provides the first comprehensive summary of the radiological conditions throughout the Marshall Islands.