In situ measurement of cesium-137 contamination in fruits from the northern Marshall Islands

Abstract

Radioactive contamination of fruits in the northern Marshall Islands, resulting from the US nuclear weapons testing program in the 1940s and 1950s, is still a human health concern, in particular pertaining to island population resettlement and the economic benefit from farming. Over 200 fruits, primarily coconuts and pandanus, were collected on 11 islands from four atolls in the northern Marshall Islands in 2017. The energy spectra from nuclear gamma decays were measured on a research vessel for each fruit in situ. From these recordings, the level of cesium-137 (¹³⁷Cs) contamination was determined for individual fruits. Comparisons of the results are made to past studies and international food safety standards. There is a broad distribution of values, ranging from below detectable radiation levels to relatively high levels; safety concerns are largest for Bikini Island. A noticeable fraction of fruits from Bikini have significantly higher levels of ¹³⁷Cs contamination compared with those from all other measured islands.

Keywords: Bikini; Marshall Islands; cesium-137; food; radiation.

Fig. 1.

Spectrum of a fruit from Bikini Island with a high concentration of ¹³⁷Cs (Left) and spectrum of a fruit from Utirik Island, with a low concentration of ¹³⁷Cs (Right). The peak at 662 keV in the Bikini fruit spectrum is a clear indication of the presence of ¹³⁷Cs.

Fig. 2.

Location of measured fruits on Enewetak Atoll (Left: Enewetak, Ikuren, Japtan, and Medren), Bikini Atoll (Middle: Bikini and Enyu), Rongelap Atoll (Middle: Naen and Rongelap), and Utirik Atoll (Right: Aon, Elluk, and Utirik). Color coding of each measured fruit was done according to the levels specified by international standards listed in Table 1: green (0 to 40 Bq/kg), blue (40 to 100 Bq/kg), yellow (100 to 600 Bq/kg), orange (600 to 1,200 Bq/kg), and red (above 1,200 Bq/kg), as presented in the legend.

Fig. 3.

(A) Comparison of the distribution of ¹³⁷Cs activity concentration measurements in coconuts and pandanus from Bikini Island. Contamination in pandanus is statistically significantly higher despite limited sample sizes (P < 0.001). (B) Comparison of the distribution of ¹³⁷Cs activity concentration measurements in fruits from Bikini Island and fruits from Enyu Island, both located in Bikini Atoll. Contamination from Bikini Island is statistically significantly higher despite limited sample sizes (P < 0.001).