Re: Patient Excreta

["Sean Austin" <seanaustin@hotmail.com>]

I have no doubt that there was measurable radioactivity in the sewerage 
from the medical facilities.  Analysis using a HPGe system would detect 
concentrations in the pCi/ml range depending on the counting time, 
sample size, etc.  Whether this was significant or not needs more 
evaluation than simply counting samples collected downstream of a 
facility.  First, the dose at the sampling point is irrelevant because 
that is not representative of what would happen under normal 
circumstances.  No member of the public would normally be exposed at 
that point.  Second, as the bolus continued downstream, you would see 
increasing dilution as more wastewater was added to the stream.  Once it 
hit the wastewater treatment facility, this is where you would really 
see the effects of dilution because of the millions, sometimes billions 
depending on the size of the city served, of gallons per day running 
through the system.  Then you would need to evaluate the continued 
effects of dilution as the treated water proceeds to the actual point of 
human intake.  Some facilities may collect freshwater from rivers, 
adding to dilution, or discharge treated water to rivers, also 
increasing dilution.  

Sludge from wastewater treatment facilities may be contaminated with 
these radionuclides, and one would need to follow this pathway to 
ingestion to fully evaluate the effects to members of the public.  But 
once you consider how the sludge is treated and disposed, and allowing 
for radioactive decay of these short-lived isotopes, I believe you would 
find that the dose is virtually non-existent.

For additional information on this, NUREG/CR-5814, PNL-7892 evaluated 
the exposure pathway from disposal of RAM into sanitary sewer systems. 
For the one case studied in this report that included medical and 
research facility operations, it was noted that the concentration of 
radionuclides in the wastewater influent, effluent, and sludge was 2% or 
less, which included common nuclear medicine radionuclides such as 
Tc-99m, Ga-67, I-131, and In-111.  While this report evaluated licensees 
discharges, and made no estimate of patient releases to the system, the 
fact that the concentrations were so low is evidence of the minimal 
impact that these activities have on the public.

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