Measurement of background gamma radiation in the northern Marshall Islands

Autumn S. Bordner; Danielle A. Crosswell; Ainsley O. Katz; Jill T. Shah; Catherine R. Zhang; Ivana Nikolic-Hughes; Emlyn W. Hughes; Malvin A. Ruderman

doi:10.1073/pnas.1605535113

Contributed by Malvin A. Ruderman, May 5, 2016 (sent for review February 18, 2016; reviewed by Makis Petratos and Ernst Sichtermann)

Significance

Sixty-seven nuclear tests were conducted on two atolls in the northern Marshall Islands between 1946 and 1958. These tests produced radioactive fallout, which even today gives rise to radiation measurable above naturally occurring background levels. Rather than obtain new data, recent estimates of contamination levels in the northern Marshall Islands use measurements made decades ago to calculate present radiation levels. In contrast, we report on timely measurements on three different atolls, and also provide detailed fits and simulated maps across several islands, including the islands of Bikini and Rongelap. Bikini and Rongelap Islands are of particular interest as they are relevant to the discussion of human resettlement; indeed, our radiation values for Bikini Island are higher than those previously reported.

Abstract

We report measurements of background gamma radiation levels on six islands in the northern Marshall Islands (Enewetak, Medren, and Runit onEnewetak Atoll; Bikini and Nam on Bikini Atoll; and Rongelap on Rongelap Atoll). Measurable excess radiation could be expected from the decay of ¹³⁷Cs produced by the US nuclear testing program there from 1946 to 1958. These recordings are of relevance to safety of human habitation and resettlement. We find low levels of gamma radiation for the settled island of Enewetak [mean = 7.6 millirem/year (mrem/y) = 0.076 millisievert/year (mSv/y)], larger levels of gamma radiation for the island of Rongelap (mean = 19.8 mrem/y = 0.198 mSv/y), and relatively high gamma radiation on the island of Bikini (mean = 184 mrem/y = 1.84 mSv/y). Distributions of gamma radiation levels are provided, and hot spots are discussed. We provide interpolated maps for four islands (Enewetak, Medren, Bikini, and Rongelap), and make comparisons to control measurements performed on the island of Majuro in the southern Marshall Islands, measurements made in Central Park in New York City, and the standard agreed upon by the United States and the Republic of the Marshall Islands (RMI) governments (100 mrem/y = 1 mSv/y). External gamma radiation levels on Bikini Island significantly exceed this standard (P = <<0.01), and external gamma radiation levels on the other islands are below the standard. To determine conclusively whether these islands are safe for habitation, radiation exposure through additional pathways such as food ingestion must be considered.

Footnotes

↵¹To whom correspondence may be addressed. Email: ewh42{at}columbia.edu or mar{at}astro.columbia.edu.

Author contributions: A.S.B., D.A.C., A.O.K., C.R.Z., and E.W.H. performed research; A.S.B. contributed new reagents/analytic tools; A.S.B., D.A.C., J.T.S., C.R.Z., and E.W.H. analyzed data; A.S.B., I.N.-H., E.W.H., and M.A.R. wrote the paper; J.T.S., I.N.-H., E.W.H., and M.A.R. designed research.
Reviewers: M.P., Kent State University; and E.S., Lawrence Berkeley National Laboratory.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1605535113/-/DCSupplemental.

Freely available online through the PNAS open access option.

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