Dear John,

The most interesting paper relating to molluscs and the Bikini bomb tests is by Kelshaw Bonham, who used the shell thickness between two lines of radioactive strontium from two successive hydrogen bomb tests to estimate the growth rate of Tridacna gigas shells ("Growth rate of giant clam Tridacna gigas at Bikini Atoll as revealed by radioautography." Science, 149:300-302, 1965.) Kelly collected a shell 52 cm long in 1964, sliced a section through it, and put it up against a piece of x-ray film in a dark closet here at UW for three months, then developed the film. The two "growth lines," where radioactivity from incorporated Sr90 in the shell in place of calcium exposed the film, thus must represent the last two series of tests, in 1956 (Operation Redwing) and 1958 (Operation Hardtack). (I was at Enewetak studying Conus in 1956, and still have my Operation Redwing photo-ID badge.) Because there
were two bands, the older had to date from 1956 and the younger from 1958, the last test. The clam must have settled before summer 1956 but after the previous test, which was in 1954. At the first band (1956) the clam was about 10 cm long, and in 1958 it was about 14 cm long. In the two years between the tests, it gained about 4 cm in thickness at the thickest part of the shell. Even tropical Tridacna has annual dark and light bands in the shell, and there were two, as expected, between the radiation bands, so its age could be determined by two methods. When collected it was about 9 years old.

Alan

On Tue, 3 Sep 2013, John Varner wrote:

> Does anyone have information on radioactivity being concentrated in shells?  In relation to the Fukushima mess, there have been
> higher than expected levels of contamination in seafood.  I expect shells from Northern Japanese waters will become more scarce as
> fishing is curtailed.  Is there any question of radioisotopes, especially strontium, which enters into biological pathways due to
> it's similarities to calcium, winding up in shells themselves?  There must be some research related to nuclear testing at places like
> Bikini Atoll and other Pacific test sites...
>
> - John
>
>