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Re: [at-l] Water Filters

At 08:00 PM 2/16/97 PST, Jim Loudon wrote:
>> I wish I COULD use iodine long term
>
>Whether you know it or not, you _are_ using iodine on a long-term
>basis, unless you've got the telltale lump on your neck...
>
>jim

Ok, ok.... pass the salt.

Rephrase that as:

	I wish I THOUGHT I COULD SAFELY use MASSIVE, BACTERIA KILLING, CYST
DEACTIVATING, doses of iodine OVER A PERIOD OF SIX MONTHS...

I cut the following out of the rec.backcountry "distilled wisdom" piece on
water purification.  The whole piece can be found at:

	http://io.datasys.swri.edu/wisdom/Panel_09_Water.html

-- Jim Mayer

*A warning about iodine toxicity* (some individuals appear to be
susceptible to this, while many are not). 

%J Animal Health Newsletter
%I University College of Veterinary Medicine
%D July 1995
%K Canine Giardia,

According to "Understanding Nutrition" by Whitney, Hamiltion and Rolfes (a
nutrition text book), iodine is "a component of the thyroid hormone
thyroxin which helps to regulate growth, development, and metabolic rate." 
"Excessive intakes of iodine can als o cause an enlargement of the thyroid
gland... [and] depressed thyroid activity.  this goiterlike condition can
be so severe as to block the airways in infants and cause suffocation..." 
Average consumption in [the U.S.] rose from 150 micrograms per day i n
1960 .. to an all-time high of over 800 micrograms per day in 1974.  It
has since decline to about 200 to 500..."  "The toxic level at which
detectable harm results is thought to be over 2,000 micrograms per day for
an adult..."  Now to the tablets..  .  My bottle of "Potable Aqua" (which
I carry as a back-up for the broken filter) has a net contents of 0.21
ounces for 50 tablets.  Here are the calculations:  0.21 oz/50 tablets ==>
0.0042 oz/tablet = 0.1191 gram/tablet; each tablet is 6.68% Iodi ne, thus
0.0668 * 0.1191 * 1,000,000 = 7,956 micrograms of iodine per tablet.  Note
that this is PER TABLET. One tablet treats a quart of water.  For Giardia
control, or if the water is cold or of poor quality, the directions say to
use 2 tablets per qu art.  (Who doesn't want to control giardia ?!!)  The
average backpacker should be drinking a gallon a day (varies widely).  One
gallon treated with iodine at the rate of 1 tablet per quart would contain
about 31,800 micrograms of iodine.  At the rate of 2 tablets per quart, it
would be 63,600 micrograms.  These levels exceed the *believed* toxicity
level by a mile.  This is the reason that prolonged use of iodine isn't
recommended, and the reason (in addition to taste/smell) that *I* switched
to a fi lter.  As for short term use I guess the relevant question is,
"How's your thyroid feeling?"

Medicine for Mountaineering, 3rd edition:
"Ingested iodine is absorbed as iodide, and an average adult requires 150 
to 200 micrograms per day.  Daily consumption of one to two liters of 
water disinfected with 8 mg/L of iodine would provide 30 to 80 times that 
amount, but such quantities would not affect most individuals with normal 
thyroid function.  Almost all patients who have developed iodide goiter 
after consuming excess iodide have consumed far larger amounts for six 
months to more than 5 years."
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