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Re: [at-l] Phenol red



In a message dated 06/22/2000 12:41:25 PM EDT, sloetoe@yahoo.com writes:

<< ### I haven't looked it up in forever, but there's a particular url which
 shows the empirical results of the efficacy of various methods of backcountry
 water purification.
 
 Household bleach was shown to be jaw-droppingly ineffectual at killing the
 nasties. >>

The URL Is:
http://www.fc.net/~tdeagan/water/one.html

I copied some of the information, it is below.

Wildbill

"Chemical Disinfectants - The effectiveness of seven disinfecting chemical
preparations ranged from only a few percent to greater than 99.9 percent,
depending on the chemical and its concentration, the contact time, and the
disinfectant demand of the water (Figure 2).  None of the disinfectants was 
more
than 90 percent effective after a contact time of 30 minutes.  After 
eight-hour
contact, the four iodine-based disinfectants, each caused a greater than 99.9
percent reduction in viable cysts.  The chlorine-based disinfectants were
clearly less effective than the iodine-based ones at both contact times."

"All disinfectants performed better with eight hours of
contact time than with 30 minutes.  Only the iodine-based compounds 
inactivated
99 to 99.9 percent of cysts, within eight hours of contact time for both 
turbid
and clear water.  As observed by Jarroll, et al (5), the 2 percent tincture of
iodine was less effective than the other iodine preparations with 30 minutes 
of
contact time, but it was as effective as the others at eight hours.  
Comparison
of our results with those of Jarroll, et al (5), is complicated by differences
between test conditions used.  However, our results generally indicate more
stringent requirements for effective inactivation of Giardia cysts.  
Differences
between cyst populations used in the two studies could account for the 
observed
differences, even though both were G. lamblia.  Cysts produced in our
trophozoite - gerbil system had consistently high intrinsic viability (>80
percent), excysted efficiently when fresh (80 to 90 percent), and have 
appeared
more resistant to halogen disinfectants than reported previously (Ongerth 
J.E.:
unpublished)."
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