Am 14.12.2009, 15:15 Uhr, schrieb Allan Jones <[email protected]>:
Take the 35S methionine i used for example: The ALI (annual limit on
intake) for this isotope is 10 mCi. I used in total for all my
experiments
less than 1 mCi. As I was not eating the stuff, worked with gloves and
tried to be reasonably careful, I assume not to have incorporated any
radiation, but even if I had 'eaten' the entire aliquot I would still
only
have doubled my annual background radiation, as it would not even amount
to
10% ALI.
32P is of course a stronger source and actually requires adequate
shielding, but still you have a dosimeter monitoring whether or not you
have been overexposed.
And even that danger is overrated. Leukemia patients used to get 10 mCi
32P i.v., that is enough to run a major lab for a year or so. And nobody
worried about their wastes, while in the lab we carefully collect
everything!
It does make sense to replace 32P by 33P though, not only is the radiation
softer, but you get a longer half life too.
There are procedures where radioactivity is irreplaceble, I used to do
enzyme kinetics on ATPases which required measuring hydrolysis as function
of [ATP] down to 10 nM or so. Given that you need to work under initial
rate conditions you can have a maximum of 10% hydrolysis, that is 1 nM in
10 uL of sample, and you need a c.v. of less than 2% for meaningful
results. Measuring phosphate liberation from gamma-33P-ATP is actually
simple, I did up to 400 time-courses a day, each with 7 data points (by
hand, not with a robot!).
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