17 Water Purification: Chemical Treatment: Iodine: Sources of Iodine:
Description
This article is from the Water Treatment FAQ, by Patton Turner with numerous contributions by others.
17 Water Purification: Chemical Treatment: Iodine: Sources of Iodine:
Tincture of Iodine:
USP tincture of iodine contains 2% iodine and 2.4% sodium iodide
dissolved in 50% ethyl alcohol. For water purification use, the
sodium iodide has no purification effect, but contributes to the total
iodine dose. Thus it is not a preferred source of iodine, but
can be used if other sources are not available. 0.4 cc's (or 8 drops)
of USP tincture (2% iodine) added to a liter of water will give the 8
mg/l (same as 8 PPM). If the iodine tincture isn't compounded to USP
specs, then you will have to calculate an equal
dose based on the iodine concentration.
Lugol's solution:
Contains 5% iodine and 10% potassium iodide. 0.15 cc (3 drops) can be
added per liter of water, but 3 times more iodine is consumed compared
to sources without iodide.
Betadyne (povidone iodine) Some have recommended 8 drops of 10%
povidone iodine
per liter of water as a water treatment method, claiming that at low
concentrations povidone iodine can be regarded as a solution of
iodine. One study indicated that at 1:10,000 dilution (2
drops/liter), there was 2 PPM iodine, while another study resulted
in conflicting results. However, at 8 drops/liter, there is little
doubt that there is antimicrobial effect. The manufacturer hasn't
spent the money on testing this product against EPA standard tests,
but in other countries it has been sold for use in field water
treatment.
Kahn-Vassher solution. By adding a sufficient amount of iodine
crystals to a small bottle, an almost unlimited supply of saturated
iodine solution can be produced. As long as crystals remain in the
bottle, the solution is saturated. Concentration of the iodine is
dependent of temperature, either condition at ambient temperature can
be assumed, or commercial models such as Polar Pure incorporate a
liquid crystal thermometer to determine dose
One criticism of this method is the chance of decanting iodine
crystals into the water being treated. This isn't that much of a
problem as iodine is very weakly toxic, but the polar pure
incorporates a collar into the neck of the bottle to help prevent
this. Another disadvantage to this method is that the saturated
iodine solution must be kept in glass
bottles, and is subject to freezing, but this is hardly an
insurmountable problem. Freezing, of course, doesn't affect the
crystals.
This is the method I use, but I do use the commercial polar pure
bottle, and refill it as necessary with USP crystals. During a
crisis, or extended camping trips I would microfilter the water first,
so a much lower dose of iodine is needed.
With the Polar Pure bottle, dosage information is provided. Otherwise
a 1 oz bottle can be used to carry the solution. The bottle is filled
with water after use. At the next use, 1/2 of the supernate (15 cc)
is poured off into a liter of water. at 68 deg. F, this will yield
a dose of 9 mg/l. To use this method with a microfilter to get a 0.5
PPM concentration,
either large batches of water need to be treated (1/2 oz to 4.5
gallons would be .5 PPM), or a TB syringe or medicine dropper can be
used to measure doses. A USP medicine dropper should give 20 drops
per ml.
Iodine can also be dissolved in alcohol to make a solution of known
concentration . I am not aware of any commercial products, but a
pharmacy could compound one for you, or you could do it your self.
One suggested formula is 8g iodine/100 cc ethyl alcohol which yields
enough solution to disinfect 250 gallons of water. at the rate of .1
cc (2 drops)/liter to give a concentration of 8 mg/l
Tetraglycine hydroperiodide (e.g. Potable Aqua) This is the form of
iodine used by the US military for field treatment of water in canteen
sized batches. Usual dose in one tablet per quart of water to give a
concentration of 8 mg/l. Two tablets are used in
cloudy or cold water or contact time is doubled. The major downside
of this product is that the product will loose its iodine rapidly when
exposed to the air. According to the manufacturer, they have a near
indefinite life when sealed in the original bottle, but
probably should be discarded within a few months of opening. The
tablets will change color from gun metal gray to brown as they lose
the iodine, and you should see a brown tint to the water after
treating.
Continue to:
My Books
