From: schultz@boulder.Colorado.EDU (Dennis Schultz)
Subject: iodine purification of water
Organization: University of Colorado, Boulder
Date:  7 Jan 93 17:03:27 GMT



A water disinfectant must be able to kill the hardiest of organisms,
especially amoebic cysts and enteroviruses, the most resistant to
disinfection of the pathogenic microorganisms.  At the same time, the
toxicity of the chemical must be very low.  A water disinfectant for
the traveler presents special requirements.  These include simplicity,
effectiveness in the presence of nitrogenous pollutants, rapidity of
antimicrobial action over a wide pH range, and immediate palatability.
The backpacker will also demand light weight.

Chloronation by Halazone in the recommended dose depends on the slow
release of 2.8 parts per million (ppm) of free chlorine for immediate
antimicrobial action.  Chlorine under ideal conditions, namely a pH of
7 or lower (neutral or acidic water) and the absence of nitrogenous
compounds, hydrolyzes to hypochlorous acid (HCLO) an excellant
germacide.  But HCLO is highly reactive and in the presence of such
nitrogen-containing compounds as amino and ammonia ions, it is quickly
converted to relatively inactive monochloramine.  Moreover, above pH 7
(alkaline water) HCLO hydrolyzes to the less active hypochlorite.

These two problems are solved in water purification plants by the
practice of breakdown chlorination, the application of sufficient
chlorine to bind with the organic material in the water while leaving
a biocidal residue of free chlorine.  But this technique requires
continual testing and is impractical for rapid treatment of small
quantities of water.  The individual must resort to simple
chlorination, the practice of adding a fixed dose of chlorine compound
to water of uncertain quality.  Simple chlorination is unpredictable
and may be useless against bacteria and enteroviruses when water is
contaminated with organic material.

Additional disadvantages of Halozone are slow solubility and a short
shelf life of five months when stored at 32 degrees C (89.6 F).
Potency is reduced 50 percent when stored at 40 to 50 C, the
temperature range one might expect in an automobile glove compartment
on a summer day.  Halozone also loses 75 percent of its activity when
exposed to air for two days.

Iodination, in contrasts, with a weak aqueous solution of 3 to 5 ppm
of elemental iodine [I(2)] will destroy amoebae and their cysts,
bacteria and their spores, algae, and enteroviruses at 25 C (77 F) in
15 minutes or less.  At near freezing disinfection requires 20 to 30
minutes at the same concentration of iodine, since germicidal potency
is roughly proportional to temperature (see chart).  Elemental iodine
does not react readily with ammonia and amino ions and therefore will
remain an effective disinfectant in water polluted with nitrogenous
wastes.  Iodine is effective over a wide pH range, hydrolyzing at pH
above 6 to hydroicdous acid, which is a faster virucide than I(2).

Iodination can be accompolished in three ways.  One method is the
addition of eight drops of two percent tincture of iodine to a quart
of water, but this results in water of less than acceptable
palatability.  A second is the addition of a tablet of
Globaline(tetraglycine hydroperiodide) to a quart of water, releasing
active iodine in a concentration of 8 ppm.  The disadvantages of
Globaline Tablets include a fixed high concentration of iodine and a
33 percent loss of their initial activity when exposed to air for four
days.  The third method is the use of crystals of elemental iodine.

The only equipment needed for iodination with crytalline iodine is a
one-once clear glass bottle, with a leak-proof bakelight cap,
containing 4 to 8 grams of USP grade resublimed iodine.  The bottle is
filled with water and capped, shaken vigourously to 30 to 60 seconds
then held upright for a few moments to permit the the heavy iodine
crystals (specific gravity 4.6) to fall to the bottom.

***** The iodine crystals are not to be used directly.*****

What is used is the water in the bottle, now a nearly saturated iodine
solution.  Disinfection is accomplished at 25 degrees by the additon
of 12.5 ml of this nearly saturated solution to one liter of water to
achieve a final concentration of 4 ppm iodine.  Since the
concentration of the saturated iodine solution varies with its
temperature, only 10 ml of iodine solution would be needed if the
bottle were kept at body temperature.  At near freezing, 20 ml of
iodine solution would be used per liter.(The cap of the iodine bottle
may serve as a measuring device.)  After a contact time of 15 minutes,
the water is disinfected.  When more disinfected water is desired, the
above steps can be repeated almost 1,000 times without replenishing
the iodine crystals.  The shelf life of crystaline iodine is
unlimited.

****************************************************************
Under usual circumstances, a 2 ppm iodine solution with a contact time of 40
minutes offers improved palability and effective disinfection.
****************************************************************

If increased germicidal potency is necessary because the water is
turbid cold, or heavily contaminated, the concentration of the iodine
solution could be increased to 8 ppm, with a contact time of 20
minutes.  However, in the interest of palatability, one may prefer not
to increase the concentration, but instead increase the contact
time.(see chart- also the iodine can be removed by heating or boiling
until the color disapates, however this is not an option for those
with limited fuel reserves.)

A clear glass bottle is recommended to permit observation of the
iodine crystals. Plastic bottles of all types take on an opaque brown
stain after long exposure to the working solution.  Furthermore,
plastic bottles tend to leak as one travels to high elevations and
distort and crack on descent to low elevations.

The toxicity of iodine is remarkably low in the concentrations used
for water disinfection.  Only persons with a specific sensitivity to
idodine, and perhaps those who have been treated for hyperthyroidism,
risk any ill effects.  The only danger of the iodination procedure is
the inadvertant ingestion of iodine crystals, although an ounce of
nearly saturated iodine solution would be harmless.  No fatality from
ingestion of less than 15 grams of iodine has been reported.
						   ^^^^^^^^
Chlorine, except when breakpoint chlorination is practiced, is an
unreliable disinfectant.  Iodination, on the other hand, rapidly
inactivates the known human pathogens, including the enteroviruses
which are the most resistant to disinfection.  Iodination is effective
over a wide pH range and in the presence of nitrogenous pollutants.
There is a need among hikers for an effective, palatable water
disinfectant with rapid action and long shelf life.  The iodine
disinfection method described above meets these requirements.


Iodine concentration versus time for total virus distruction
(asci approximation)

ppm
7	*
6		*
5			*
4			   *
3			      *
2				*
1					*
	20	30	40	50	60

time in minutes for total virues distruction at 25 C.

________________________________________________________________

Concentration in storage bottle at useful temperatures

Temperature	volume	concentration	capfuls*

 3 C( 37 F)	20.0 ml	200 ppm.	8
20 C( 68 F)	13.0 ml	300 ppm.	5+
25 C( 77 F)	12.5 ml	320 ppm.	5
40 C(104 F)	10.0 ml	400 ppm.	4

* assuming a capful is 2.5 ml (into 1 liter makes 4ppm)

CONCENTRATION IN
STORAGE BOTTLE



This is a summary of,

Kahn, F.H., and B.R. Visscher (1975), "Water disinfection in the wilderness--
a simple, effective method of iodination," West. J. Med. Vol.122:450-3.

Other references that may be of interest,

Zemlyn, S. et al., (1981), "A caution on iodine water purification,"
West. J. Med. Vol.135:166-7.

Jarroll E.L., et al., (1980), "Inability of an iodination method to destroy
completely giardia cysts in cold water," West. J. Med. Vol.132:567-9.

Myhre, B.A. (1987), "A method of reducing the iodine taste of water purified
in the wilderness," West. J. Med. Vol.146:365-6.


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