RADIATION DOSES FOR MARSHALL ISLANDS ATOLLS AFFECTED BY U.S. NUCLEAR TESTING: ALL EXPOSURE PATHWAYS, REMEDIAL MEASURES, AND ENVIRONMENTAL LOSS OF ¹³⁷Cs

Abstract

Radiation doses calculated for people resettling Bikini Island at Bikini Atoll, Enjebi Island at Enewetak Atoll, Rongelap Island at Rongelap Atoll, and Utrōk Island at Utrōk Atoll are presented. Residence is assumed to begin in 2010. In previous dose assessments it was shown that ¹³⁷Cs accounts for about 98% of the total dose for returning residents. About 85 to 90% (depending on the atoll) is via consumption of locally grown foods containing ¹³⁷Cs, and about 10 to 15% is due to external exposure from ¹³⁷Cs in the soil. These assessments were made using only the radiological half-life of ¹³⁷Cs (30.1 y). We have shown since that there is an environmental loss of ¹³⁷Cs from soil to groundwater that results in a more rapid loss of ¹³⁷Cs from the atoll ecosystem. The mean effective half-life of ¹³⁷Cs at the atolls is 8.5 y. Moreover, treatment of coconut trees with potassium (K) reduces ¹³⁷Cs concentration in drinking coconut meat at Bikini Atoll to about 5% of pretreatment concentrations. The magnitude of reduction is dependent on the concentration of ¹³⁷Cs in soil, and thereby in food crops, and is less for Enjebi and Rongelap Islands than for Bikini Island. Treatment of food crops and fruit trees with K and removal of the top 15 cm of soil around houses and community buildings prior to construction to reduce external exposure where people spend most of their time has been presented to the communities as a “Combined Option” remediation strategy. Doses presented here are calculated using the Combined Option, effective half-life of ¹³⁷Cs at the atolls, and a diet of both imported and local foods. The average natural background dose in the Marshall Islands, plus the anthropogenic nuclear test-related dose at Bikini, Enjebi, and Rongelap Islands, is less for each of the islands than the average background dose in the U.S. and Europe.