US government nuke boffins say that Bikini atoll and other Pacific islands blown up by America in 1950s atomic-bomb tests are now entirely safe to live on - in fact they are safer, from the point of view of radiation dose, than living in Europe or the continental USA.
According to Lawrence Livermore nuke lab boffins Bill Robison and Terry Hamilton, nearly all the danger posed in living on Bikini, Enjebi and Rongelap islands results from caesium-137 left behind after the atom tests. When decaying radiologically 137Cs has a half-life of 30 years, meaning that even now a quarter of the malevolent stuff remains. Other hazards such as strontium are insignificant.
However Robison and Hamilton say that the 137Cs in the soil of the islands has also been washed into groundwater by rain. The groundwater in those parts circulates with the ocean around it, meaning that Caesium is lost into the sea and remaining levels are much less than would have been expected. Actual radiation received simply by walking about is no longer a big deal.
However 137Cs is also absorbed by crops grown locally, and it is much more dangerous if ingested: so much so that ingestion of caesium in island food such as coconuts, breadfruit and Pandanus accounts for 90 per cent of the radiological hazard of living in the former fallout zone.
The Lawrence Livermore boffins, however, have found that if crops are treated with potassium fertilisers this displaces the caesium, reducing it to 5 per cent of the untreated level with no ill effects. They say that provided plants are potassium treated, and other simple measures taken, someone living on Bikini atoll would nowadays be radiologically better off than most of us. The US has a programme providing help of this sort to Marshallese already returned or those wishing to resettle the islands.
"If this approach is taken, the natural background dose plus the nuclear-test-related dose at Bikini, Enjebi and Rongelap would be less than the usual background dose in the United States and Europe," says Hamilton.
The scientists add that most of the contamination suffered by the islands was the result of a mistake by boffins conducting the "Castle Bravo" hydrogen bomb test in 1954. The designers had expected the weapon to yield around five megatons of energy: in the event it went off with 15-megaton force, vapourising much more of the surrounding island and reef than had been anticipated and throwing a much bigger fallout cloud to contaminate the area downwind.
The Rongelap islanders in particular suffered a nasty surprise as they had not been told about the test, which was supposed to be secret. The crew of a Japanese fishing boat was also contaminated in the accident.
Locals may be sceptical of the new announcement, as the US government had said it was safe to return as long ago as the 1970s. The issues with contaminated food emerged subsequently.
The new island radio-health research is the cover article in the latest issue of Health Physics. ®