Re: Cs-137 in "Contaminated" wood

[RADPROJECT@aol.com]

In a message dated 98-06-28 17:29:45 EDT,  Ernest Goitein writes:

<< I have followed the thread about Cs release from Spain with interest.
Your
 comments and those of Tony LaMastra were very informative.   

 I have questions about the radioactivity in wood.  I suppose that the
 contamination is the result of fall out from atmospheric tests and the
 consequent uptake by trees from contaminated groundwater or soil. 
 
 If trees absorb Cs, what about other vegetation including produce and further
 up the food chain such as milk and meat products?
 
 Also isn't the distribution of  the fall out more prevalent in the Northern
 and Eastern part of the US?   >>

Ernest: 

The major source of Cs-137 uptake by trees in the survey I conducted in 1990
[I was working at a utility run Environmental Lab in the Northeast at the
time] ,  appears to be initial uptake directly through tree leaves during the
peak years of atmospheric Cs-137 depostion from open air tests. Trees have
active uptake mechanisms for airborne Cs through foliar absorption documented
in studies in Begium from Chernobyl fallout. What was measured and reported in
the nationwide study of Cs-137 I mentioned as presenting at the HPS Annual
meeting in DC in 1991 clearly shows trees to be marvelous integrating
indicators of exposure to airborne Cs-137 levels.

The activity measured in my survey in trees (up to 300 pCi/kg of wood and
30,000 pCi/kg of ash) cannot be explained by soil concentrations based on
nuclear fallout which average in the Northeast only 100 to 300 pCi/kg of soil.
This would imply a Biv (using terminology of RG 1.109) or transfer factor from
soil to plant [pCi/gm of plant per pC/gm of soil] for Cs-137 of 1.0 or more!!
RG 1.109 provides a value for Cs-137 Biv of 0.01. The highest Cs-137 levels I
personally measured in woodash were observed in northern Florida with Cs-137
over 30,000 pCi/kg of ash. The general total areal Cs-137 fallout deposition
in FL is about 20% to 30%  less on average than in the Northeast [about 100 to
140 mCi/sq. km] yet the Cs-137 levels in woodash from trees grown in FL are
50% higher. CA with Cs-137 deposition about one half of the Northeast has
Cs-137 levels in trees about 100 times lower per the survey results in my
paper.  Of major note to my original comments, domestic burning of wood ash
despite it occuring at red hot temperatures appears to volatilize almost none
of the Cs-137 in the wood. Interestingly, when I first raised the question as
to the potential Cs-137 content of woodash to a Ph.D. Lab Director of the
facility at which I was working, I was adamantly told that woodash from a
fireplace or woodstove would "not contain a single atom of Cs-137" because a
woodstove burns so hot. When I submitted three samples of woodash from a
fireplace in northern Vermont as blind enviromenatl sample replicates for
gamma spec analysis as part of my QA program duties on all lab analytical
processes [I was QA Manager at the time], Cs-137 was measured at over 15,340
+/- 76  pCi/kg of ash making the woodash sample the most contaminated
environmental media the lab had ever analyzed in over 14 years of operation,
having analyzed over 100,000 samples.  The several measurements of ash did
meet lab precision criteria for Cs-137 and other isotopes reported. But the
major issue of intellectual interest was the Cs-137 activity total counts in
these first samples exceeded the counts for every other natural isotope
present. So much for dogma. Or as Alf once said: "Dogma, dogma, dog manure".
Subsequent measurements made of woodash from a similar species of  tree [oak]
in  southern Vermont near an operating nuclear plant showed Cs-137 levels at
1,587 +- 57 pCi/kg, about one-tenth the level in northern Vermont. At that
time I called for a survey in woodash in the April 1990 HPS Newsletter Feature
Article ["Preliminary Study of Cs-137 Uptake by Trees...."] because it was
rather obvious that had the level of Cs-137 in woodash from near a randomly
picked nuclear plant been 10 times higher than a sample taken 120 miles
distant, quite unjustified claims as to plant impact and releases could have
been made.

What is probably occurring here is that all trees growing at the time of
active open air testing of nuclear bombs,  took up a certain level of Cs-137
during the peak years of fallout in the early 1960s. What is being measured in
the 1990s in the wood ash from these mature trees is a long-term equilibrium
concentration based on excretion of Cs-137 to the soil around the tree and re-
uptake from the roots influenced by soil chemistry factors touched upon in my
HPS paper from 1991.

The levels of Cs-137 in plants grown in soil using ash having elevated levels
of Cs-137 can be calculated but are likely to be significantly overestimated.
Woodash from mature trees does contain Cs-137 with up to 30,000 pCi/kg of ash.
Wood ash is being widely used on gardens both domestically and on a commercial
scale. Certain, organic farming co-ops in Vermont grow crops for distribution
to organic stores like Bread and Circus on large farms which use woodash from
wood burning power plants (several thousand tons per year mixed with manure
and spread on the fields). The ash is likely depleted of a good fraction of
the Cs-137 originally in the wood due to the high temperature combusion in an
industrial boiler like a power plant [my original comments] but the ash will
still be adding some Cs-137 to the soil [perhaps the ash contains Cs-137 at a
few thousand not 20,000 pCi/kg of ash]. However Bread and Circus runs
advertisements opposing food irradiation, yet is growing its "organic" produce
in field to which Cs-137 is being  added due to the use of woodash with
incremental fallout activity. Go figure.

However, woodash is about 10% potassium by weight and potassium added to soil
in woodash will most likely suppress the uptake of Cs-137 added with the ash
plus what is already in the soil such that the plants grown will have less
Cs-137 than would have been found in plants grown before the woodash was
added!! Of course calculations using standard models of uptake of
radioactivity from soil with supplemental contamination such as those from  RG
1.109 would predict just the opposite-ie more contamination in soil yields
more contamination in plants. However, these simple models are unlikely to
apply to woodash related soil contamination buildup because they fail to
consider the stable mineral content of woodash. Unfortunately, no one has ever
conducted studies of the use of woodash as fertllizer to really document what
is really happening. 

Similarly woodash commonly has Sr-90 at concentrations even higher than
Cs-137. But wood ash is about 30% stable Ca by weight and woodash added to
soil will suppress the uptake of preexisting Sr-90 and the added Sr-90 such
that the plants grown will have less Sr-90 that would have been found in
plants grown before the woodash was added!!


Stewart Farber, MS Public Health
Consulting Scientist
Public Health Sciences
19 Stuart St.
Pawtucket, RI 02860

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