FW: Storage Period for Urine Bioassays

["Carbaugh, Eugene H" <gene.carbaugh@pnl.gov>]

The "possible storage period" can be very long (i.e., years and years -
centuries?).  The issue is sample preservation during storage.  Although urine
is normally sterile when excreted from the body, it is an excellent growth
medium for all kinds of bacteria, etc.  A highly acidified sample will prevent
bacterial growth.  Freezing samples should also effectively halt biological
activity.  Unless the radiological half-life is an issue, the radioactivity will
still be there - the problem then becomes simply one of making sure you recover
the sample fully from the container.  If raw urine sits a long time at room
temperature or refrigerated temperatures you will get some sedimentation and
gradual bacterial growth from bacteria present in the air, in the bottle prior
to collection (less likely if you use sterile sealed containers, but even then
some slight bacterial contamination will probably occur during collection).
Plateout is also a well-known phenomenon in samples but is typically dealt with
by good acid wash techniques.  It would be a good idea to include some known
spiked samples along with your stored "real" samples.  

A few years back at Hanford we had to freeze 1-liter Nalgene bottles of worker
samples while arranging a new analytical support lab.  Some samples were frozen
for 6 months or more (including our spiked controls) and our service labs had no
problem recovering any plateout by good acid wash techniques.  Yes, we had lots
of good stories about "iced pee," particularly when the weather got hot.

My personal preference would be to preserve your samples upon collection if its
going to be more than a few days before processing.  That simply eliminates the
problem of biological ingrowth.  If processing in an onsite lab, preserve by
refrigeration or acidifying.  If you need to send them offsite, freezing them is
a nice alternative to shipping acidified samples which have to be considered
hazardous materials.  Test your sample containers first to make sure they won't
crack upon freezing, and then probably ship them (frozen) in an ice chest.

Thank heavens we haven't had to deal with this problem for a number of years
now.

Gene Carbaugh, CHP
Internal Dosimetry
Pacific Northwest National Laboratory
Richland, WA 
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html