AJ Hicks questions [OGD V6#370] the chemistry behind my recommendation of
bleach as a virtually instantaneous sterilization agent. He cites the odor of
chlorine in bleach as evidence of the volatility of hypochlorite. He is
correct that the manufacture of bleach involves the uptake of gaseous chlorine by
a very alkaline solution of lye but he got the chemistry wrong.
Hypochlorite is generated by the following equation:
Cl2 + 2OH- <---> ClO- + Cl- + H2O
Although the equilibrium lies strongly to the right, there is always
some free chlorine present, which accounts for its odor in bleach; if a small
portion of the chlorine escapes as gas, the equilibrium compensates for this by
shifting slightly to the left and supplying replacement elemental chlorine.
Thus there is always an odor of chlorine coming from bleach without an
appreciable portion of it escaping into the atmosphere. Therefore, as I originally
stated, no confinement is necessary for bleach to be effective. Even my
wife knows this when she does the laundry.
The formation of hypochlorous acid at low pH is of no consequence since
the pH of bleach is high, therefor the statement, "But if one were to drop
the pH of the second solution..." is irrelevant. The sodium ion, Na+ has
nothing to do with it! Yes, acidification could release a lot of chlorine gas,
but this, too, is irrelevant since we do not normally add acid to bleach, nor
can I figure out why we would ever want to do such a foolish and dangerous
thing.
I know how fast bleach reacts with cellular material, but the details of
contradicting field tests are not given. Perhaps the bleach was too dilute,
or perhaps the experimentor did not understand the need to conduct tests
with reasonably fresh bleach, or perhaps his tests for live virus were
contaminated by external sources of virus. If the experimentor did not understand
the
underlying principles of destruction of virus by bleach perhaps his technic
was flawed.
AJ repeats one of the most ridiculous myths of orchidology, namely that
there is something mystical about TSP. I am surprised he didn't complete the
myth by mentioning that undissolved crystals must be at the bottom of the
container, otherwise the magic doesn't work. The antiviral activity of TSP
arises from its extremely high pH. You can get the same results by adding 1
teaspoon of lye to a gallon of water. The statement by AJ that TSP is a more
effective sterilizing agent than bleach is not even close to true. If the
phosphate in TSP contributed to its sterilizing ability, why would we expose our
precious orchids to phosphate in our fertilizers? Phosphate, like calcium, is
not an "enemy" of orchid growth but a "friend."
Virkon S is cited as a chlorine based disinfectant, but it is NOT
chlorine or hypochlorite, which we are discussing. Table salt is also chlorine
based, but has minimal toxicity unless we are prone to hypertension.
A compendium of orchid viruses is included by AJ without explanation of
what relevance it has for the effectiveness of bleach in destroying virus.
I apologize for being so harsh in responding to AJ's criticisms, but I
habitually crusade against myths of orchid culture that are repeated from one
orchid grower to another with strong conviction, but are nevertheless without
firm scientific support. Growing orchids properly is challenging enough
without paying blind respect to these extraneous myths.
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