As a Pleurothallid grower very concerned about preventing the
introduction and spread of Bean Yellow Mosaic Virus in my collection,
I am interested in information about sterilizing tools and pots.
Chemistry isn't my strong point, so I checked with a friend who knows
this kind of stuff and he double checked with a colleague and here is
what I was told:
- household bleach is ~3-7% solution of
sodium hypochlorite NaOCl (also known as
sodium oxychloride). You can purchase
industrial strenght which is >10%
- it is often mistakenly called chlorine bleach
since chlorine is used to make it. There is
no chlorine gas in bleach.
- bleach sterilization is provided via liquid
not from delivery of Cl2 gas
- a sodium hypochlorite and water solution
will provide both
hypochlorous acid (HOCl) and
hypochlorite ion (OCl-) (that's OCl with a negative 1 charge)
- hypochlorous acid and hypochlorite ion both provide
sterilizing action by oxidizing organic compounds
- oxidation is not specific. HOCl and OCl- can react
with lipids in cell walls and membranes - to 'break open'
bacteria, fungi and viruses. - HOCl and OCl- can also
react with proteins and nucleic acids within the cell
- HOCl is the stronger and faster oxidizer (reacts within
seconds) and OCl- is the weaker slower oxidizer
(minutes -10's minutes). Also, due to ionic charge, OCl-
doesn't penetrate cell walls well.
- the distribution between HOCl and OCl- is
dependent upon solution pH. (Table appended)
- note as HOCl is used up (if pH is constant)
OCL- will shift to HOCl to keep constant ratio
- HOCl is less stable and evaporates more readily.
Therefore OCl- goes to HOCl, HOCl evaporates...
So if your bleach solution is low pH its effective
lifetime is very short.
- many disinfecting solutions are sold with added
stabiliziers to keep pH constant and minimize loss
of solution effectiveness. You can minimize loss but
you can't stop that HOCl <--> OCl- equilibrium.
So all bleach solutions lose their effectiveness over time;
it's just a matter of how quickly.
- 24 seconds may be sufficient for sterilization
of organic contaminats from non-porous surfaces.
So wiping suraces with a bleach solution really
does kill stuff.
- I suspect extended exposure times (hours) are necessary to
enable diffusion of liquid sterilizing solution into
the porous media. 24 hours seems a common recommendation
for anything that takes more than 4hours. Nobody wants to
wait 4 hours - so they put it to soak and take it out tomorrow!
pH % as HOCl % as OCl-
8.0 22 78
7.8 33 67
7.5 48 52
7.2 66 34
7.0 72 34
6.0 96 4
5.0 100 0
At very low pH you will produce Cl2 gas
- but that's another story
========
END
--
Marni Turkel
Stony Point Ceramic Design
2080 Llano Rd 1B
Santa Rosa, CA 95407
Phone 707-579-5567
Fax 707-579-1116
Web www.marniturkel.com
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