Public In Vivo Iodine-131 & Tritium Urine Levels

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

The Hanford whole body counter cycles some 7,000 to 11,000 whole body
counts in a year, mostly on Hanford workers.  Our NaI system has a
nominal MDA of about 3.3 nCi (120 Bq) for I-131 and our germanium system
MDA hits about 1.5 nCi (55 Bq).  We are not seeing I-131 in workers at
these levels.  On the rare occasion when we do find it, we almost always
find that the worker or a family member underwent some kind of
diagnostic or therapeutic therapy. 

The most interesting anecdote was last year when a worker was found to
have moderate contamination on two consecutive days during exit through
portal monitors.  The poor guy was being called on the carpet for bad
work practices and the radcon people were getting ready to go survey his
house, afraid that he had taken stuff home.  We did a whole body count
on him before they left and found 24 nCi (890 Bq) of I-131.  Since we
don't really have I-131 anymore, we posed the question of medical
exposure:  lo and behold, his wife had just had therapeutic dosages and
he hadn't made the connection.  We moved fast to tell radcon that if
they decided to go ahead with home surveys to be prepared to find lots
of non-Hanford I-131 - and start to think about how they were going to
write that one up.  Fortunately, wise heads prevailed and the home
survey plans (and appropriate press releases) were quickly halted.  We
told the field radcon people they owed us a beer - but they never paid
up.

Regarding tritium - we run occasional blank urine samples through our
excreta bioassay lab as a QA check on their work.  Based on our blanks,
the lab has an MDA of about 4.4 dpm/ml  (thats 2000 pCi/l, or 33 Bq/l),
and an Lc of 2.5 dpm/ml  (800 pCi/l, 13 Bq/l).  Actual sample results
are in the range of about 1 +/- 0.73 (1-sigma) dpm/ml (you do the next
conversion). I believe these levels would be indicative of the general
public in Eastern Washington State. 

A few years back we did some sampling on a group of unexposed workers
who got their workplace drinking water from an aquifer that had slight
tritium contamination from old waste management practices.  Their levels
showed a lognormal distribution with a geometric mean of about 3 dpm/ml.

A person who wears a tritium-activated luminous watch may come in one or
two orders of magnitude higher.

Hope this is useful.  Feel free to e-mail or phone me if you need more
info.

Gene Carbaugh, CHP
Internal Dosimetry
Pacific Northwest National Laboratory
Richland, WA 99352
(509) 376-6632

e-mail:  gene.carbaugh@pnl.gov