°
Contamination outside the defined area: Environmental assessment samples (soil,
vegetation) suggested that fall-out contamination was not confined to Rongelap
and Utirik.
e
Radioactivity measured on “unexposed” atoll: An instrument measured dose at
Ailuk, previously classified as "unexposed" was 0.01 Gy/h (1.0 rad/h) one hourafter
detonation.
e
Plume reconstruction probably was inaccurate: A computer simulation using all
available meteorologic data indicated that the initial path of the fall-out cloud
followed was in an easterly direction, but then it shifted to a south/southwesterly
direction. This computer simulation was criticized later as being based on wind
data that was too sparse to provide sufficient support for conclusions as to the
trajectory of the radioactive cloud.
e
The prevalence of thyroid nodules among populations classified as "unexposed":
Thyroid nodules ranged from 1-10.6% amongresidents of atolls previously thought
to be "unexposed" compared to 2.4% background prevalence in two southern
islands farthermost from Bikini, a statistically significant increase. A well-designed
retrospective cohort study of thyroid neoplasia in 7,266 Marshall Islanders from 14
atolls of which 2,273 were alive in 1954 and were potentially exposed to Bravo fallout was published in 1987.
3.4.2
Duration of Follow-Up
Follow-up of the exposed cohort differed from that of the unexposed group.
Follow-up of the exposed group began in 1954, whereas it did not begin until 1957 for the
unexposed group, and some deaths among the unexposed group already had already
occurred during the intervening three years.
33