Sr-90 in the environment

[Holloway3@aol.com]

In a message dated 8/14/00 9:06:13 PM Pacific Daylight Time, 
radsafe@romulus.ehs.uiuc.edu writes:

Norm writes:

<< As to Sr-90, the claim is that, since atmospheric nuke tests stopped in 
the USA
 and Russia after the signing of the Partial Test Ban treaty, and that other
 countries, like France and China, stopped soon after (sorry dont\'t have 
those
 exact dates), that Sr-90 levels should fall every year per the rate of decay 
of
 Sr-90. But, starting the in 1980s, Sr-90 levels have not fropped any further 
and
 have in fact increased. You can check all this at www.radiation.org
 So, the question is - where is the Sr-90 coming from? >>

Norm,  I checked the URL that you give above and could not find enough actual 
data to provide confidence in the claim that is being made, that Sr-90 levels 
have not dropped much since 1980.  I did find a few statements that are 
false.  Before I get into those statements,  I will comment on your statement 
above that Sr-90 levels should fall every year.  Sr-90 has a half-life of 29 
years, so given the natural statistical uncertainty of measuring Sr-90 in the 
environment, one would not necessarily expect declines every year because 
when something has a 29 year half - life, the decline due to decay  in one 
year is only about 2 percent and can be overwhelmed on a short time scale by 
the uncertainty of sampling and measurement.  Now to comment on some of the 
statements by Sternglass found on the Tooth Fairy homepage:  

1. "The levels of Stronium-90 should have dropped down to near zero once 
humankind stopped exploding nuclear weapons in the atmosphere. Instead the 
levels stayed essentially the same as during the bomb-test years, or in some 
areas they even increased."

My comment:  Sternglass does not explain what model he uses to conclude that 
Sr-90 levels should have dropped down to near zero.  Considering radioactive 
decay alone,  Sr-90 levels should have dropped by about 50% from 1965 to 
1995. Inputs from Chinese testing and Chernobyl are minor compared to the 
inventory present in the environment in 1965, shortly after Russian and 
American testing ceased.  
-----------
"After reaching a peak in 1963, Strontium-90 levels in the U.S. declined 
steadily but did not disappear entirely due to ongoing French and Chinese 
aboveground testing as well as releases from U.S. and U.S.S.R. underground 
testing and from a growing number of civilian reactors. With the end of 
French and Chinese tests in 1980, the projected rate of decline should have 
dropped Strontium-90 levels to about 0.1 picocuries/gram by 1990, according 
to Dr. Jay M. Gould...."

My comment: Gould makes a mistake here when he claims that Sr-90 did not 
disappear entirely due to French and Chinese aboveground testing.  The 
statement would be true only if it were limited to Sr-90 in the atmosphere 
but it seems that in this context he is referring to Sr-90 in the general 
environment.  Even without French and Chinese testing, there would still be 
plenty of Sr-90 in the soil due to the Soviet and American testing prior to 
the test ban treaty.  It is not clear how he arrives at the predicted level 
of 0.1 pCi per gram since this is a greater decline than would be expected 
from radioactive decay alone, if levels were 1 to 2 pCi per gram in the late 
1950s in teeth.  Sternglass and Gould seem to be projecting a far greater 
drop in Sr-90 in the environment and in teeth than can be accounted for by 
radioactive decay alone. They do not make clear what other factors they are 
invoking if any.  

"The fact that we're finding numbers at much higher levels than we expected 
indicates that the dangers from radiation in our diet were not eliminated 
with the cessation of atmospheric bomb testing," Dr. Gould said. 
"Strontium-90 is still persisting in the human environment."

My comment:  Gould seems to be setting up a strawman argument here, since no 
well informed person would have expected that Sr-90 would be eliminated from 
the diet until many years after the end of atmospheric testing.  It may 
require 200 years or more for Sr-90 in the environment to reach undetectable 
levels even if there are no new inputs.  


"The RPHP researchers attributed some of the new radioactive fallout to the 
accidents at the Three Mile Island reactor in Pennsylvania in 1979 and at the 
Chernobyl reactor in Russia in 1986. In addition, they noted that state and 
federal records show a large amount of officially reported airborne emissions 
during the early 1980's from four nuclear reactors located in the vicinity of 
Suffolk County, the area from which the majority of the RPHP teeth were 
collected."

My comments: The above quote is nonsense.  I personally measured Chernobyl 
fallout in Nevada after the accident and am aware of other measurements made 
at that time.  By the time the fission products reached the United States, 
most were at barely measurable concentrations.  Chernobyl fallout was 
extremely minor in the United States, several orders of magnitude less than 
that already present due to atmospheric testing.  To claim that it is a 
significant and measurable source of Sr-90 in teeth shows their ignorance of 
the topic.  In other publications they have made the claim that Chernobyl 
fallout produced various adverse health effects in the United States.  That 
claim is nonsense and one of the most stupid claims I have ever seen in 
science.  Next time, Norm, I will tell you what I really think! 
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