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. 2016 Jun 21;113(25):6833-8.
doi: 10.1073/pnas.1605535113. Epub 2016 Jun 6.

Measurement of background gamma radiation in the northern Marshall Islands

Autumn S Bordner  1 , Danielle A Crosswell  2 , Ainsley O Katz  2 , Jill T Shah  2 , Catherine R Zhang  2 , Ivana Nikolic-Hughes  3 , Emlyn W Hughes  4 , Malvin A Ruderman  5
Affiliations

Measurement of background gamma radiation in the northern Marshall Islands

Autumn S Bordner et al. Proc Natl Acad Sci U S A. .

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 (137)Cs 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.

Keywords: Bikini; Marshall Islands; gamma radiation; nuclear testing; nuclear weapons.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Simplified map of the Marshall Islands indicating the research team’s trajectory and visited atolls. Only the visited atolls and islands are shown on the map.
Fig. 2.
Fig. 2.
Measured gamma radiation levels on each island (log scale). The purple curve represents the fitted distribution of measured radiation levels on the control island, Majuro. The vertical axis is scaled differently for different islands to account for varying radiation levels. Enewetak Island, n = 137; Medren Island, n = 91; Runit Island, n = 20; Bikini Island, n = 137; Nam Island, n = 52; Rongelap Island, n = 332.
Fig. 3.
Fig. 3.
Measured and interpolated external gamma radiation on different islands (mrem/y). The scale for magnitude of radiation is different for each island. (A) Enewetak Island, Enewetak Atoll (n = 137). (B) Medren Island, Enewetak Atoll (n = 91). (C) Runit Island, Enewetak Atoll (n = 20). (D) Bikini Island, Bikini Atoll (n = 137). (E) Nam Island, Bikini Atoll (n = 52). (F) Rongelap Island, Rongelap Atoll (n = 332).
Fig. S1.
Fig. S1.
Distribution of external gamma radiation data assessed during single location sensitivity test in Central Park (n = 100). The histogram represents empirical measurements and the curve represents the distribution fitted to these measured values.
Fig. S2.
Fig. S2.
Distribution of measured gamma radiation levels on each island, by atoll. Both the horizontal and vertical axes are scaled differently in the different panels to account for varying radiation levels and sample sizes, respectively. Bikini Island, n = 137; Nam Island, n = 52; Enewetak Island, n = 137; Medren Island, n = 91; Runit Island, n = 20; Rongelap Island, n = 332, Majuro Island, n = 19.
Fig. S3.
Fig. S3.
Mean and maximum background adjusted external gamma radiation on each island, compared with the RMI/US government agreement for safe habitation of Rongelap (100 mrem/y for maximally exposed individual). (Left) Range of adjusted external gamma radiation (mrem/y), with height of the bar representing the mean of observed values. (Right) Adjusted maximum observed external gamma radiation (mrem/y). Values adjusted by subtracting the Majuro background control. Bikini Island, n = 137; Nam Island, n = 52; Enewetak Island, n = 137; Medren Island, n = 91; Runit Island, n = 20; Rongelap Island, n = 332.
Fig. 4.
Fig. 4.
Adjusted external gamma radiation on each island, compared with the RMI/US Agreement standard for safe habitation of Rongelap (100 mrem/y for maximally exposed individual). Values adjusted by subtracting the Majuro background control. Dots represent the mean value and error bars represent ±1 SD. Enewetak Island, n = 137; Medren Island, n = 91; Runit Island, n = 20; Bikini Island, n = 137; Nam Island, n = 52; Rongelap Island, n = 332.
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