The heavens did open, and through the rent the mighty voice of [EMAIL PROTECTED] spaketh thusly:
>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. I was challenging the assertion that hypochlorite is not volatile. I do not challenge that it escapes in the form of chlorine. An open vessel of sodium hypochlorite or calcium hypochlorite will lose its efficacy as the concentration of hypochlorite diminishes. I don't disagree that there is no requirement for confinement when in use, but there is a requirement for replenishment of a solution that has been allowed to air overnight or longer. >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. The pH of disinfection chemistry involving the hypochlorite ion is of great importance. Acidification of dilute (and it must be stressed- DILUTE) solutions of bleach is perfectly safe; see any of the literature by our own Fred Bergman, including "The Disinfection of orchid seed," from The Orchid Review 103: 217, 219; "Disinfecting orchid seed," from the AOS Orchids (1996, pp. 1078-1079); "Orchid deed disinfection: the effects of pH and temperature," from The Orchid Review 104: 245-247; "Seed sowing the easy way," The Orchid Review 104: 23-25; most of section 4.3 from my own text on the subject; and any text on hypochlorite chemistry. Hypochlorous acid is the more effective form of active chlorine, and it prevails at lower pH. Along these lines, dichloroisocyanuric acid (DCCA) when dissolved in water forms active chlorine at a slightly *acidic* pH. It is now the "new" pool chlorine, judging by the labels at the local hardware store, replacing calcium hypochlorite. Acidified (or buffered) solutions of hypochlorite are used every day in plant tissue culture labs around the world for producing solutions for disinfesting seeds and other tissues without the corresponding issues of tissue damage from high pH. As for the Na+, I simply kicked it in to make the equation complete. I'm sure I'd be explaining myself if I had left it out, too. >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. I specifically mentioned high pH in 6:370: "The reason is fairly simple: the very high pH of a saturated TSP solution is sufficient to denature viruses." Nothing about TSP being "magic." The reason TSP is used is that it is far less caustic than sodium hydroxide; a saturated solution has been used since at least the 1960's for virus control as it is far easier for people working in the field to produce a saturated solution than to measure. This is in protocols from North Carolina State University's plant pathology department, where it was originally suggested to use saturated TSP in the field to prevent spread of tobacco mosaic virus. Lye caused too much tissue damage. Saturated TSP works; there's really no reason to use a lower concentration. >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." Doc, you're putting words in my mouth again. To quote what I said: "It is not at all clear that chlorine is the effective component in bleach for disinfection of tools in any event; trisodium phosphate works as well or better, even with no chlorine in it." I didn't attribute activity to the phosphate. In fact, I refer you to Broadbent's paper on the subject (The epidemiology of tomato mosaic, part III: Cleaning virus from hands and tools) in which they demonstrate that the greatest efficacy was with trisodium phosphate (Na3PO4), in comparison to (among several other compounds tested) sodium dihydrogen phosphate (NaH2PO4) and dibasic sodium phosphate (Na2HPO4). Clearly it's not the phosphate component, and I never argued it was. TSP is simply a convenient delivery system for a high pH solution that is suited to destroying viruses without undue tissue damage. Both bleach and saturated TSP do quite well in preventing virus spread. TSP usually edges out bleach in field trials from the papers I've read on the subject. "Diversol" also works quite well, if you can get it: halogenated trisodium phosphate + potassium bromide. This would give you hypochlorite at a very high pH, and oxidize the bromide to hypobromite, another effective disinfectant. >Virkon S is cited as a chlorine based disinfectant, but it >is NOT chlorine or hypochlorite, which we are discussing. Virkon S has several modes of activity, including the formation of hypochlorite in solution. It consists of potassium peroxymonosulfate, malic acid and sulfamic acid, Sodium hexametaphosphate (buffer), sodium chloride, and a detergent. Virkon has a very nice chart of the Haber-Will-Statter reaction through which Virkon forms hypochlorite/hypochlorous acid. http://www.biosafetyusa.com/reports/hws_reaction.swf And I quote: "The adduct is then hydrolyzed to generate some hypochlorite (again a biocide), and then this breaks down to give some chloride ions and oxygen etc. The chloride ions generated then react with [potassium peroxymonosulfate] and the cycle starts again." I provided the Virkon as an illustration that while high pH may not be required for deactivation, even hypochlorite/hypochlorous acid is not absolute in its ability to stop plant viruses. I'd be interested in any literature on low pH, active chlorine-based disinfectants used to control plant viruses. >A compendium of orchid viruses is included by AJ without >explanation of what relevance it has for the effectiveness >of bleach in destroying virus. The explanation was (and remains): "In short, the refereed literature on plant viruses affecting orchids indicates that the highest TIP (10 minute exposure, for those that were wondering) is 90 degrees. If anyone has any data that contradict this, I'd be interested in hearing about it." In short, the available literature values for orchid viruses are that they are quite thermally labile at temperatures well below that required to clean one's oven. Not that anybody said they weren't; it's just a public service I provide for free. This was in light of the assertion that "I would sooner be suspect of the oven than an exposure to good strong bleach." >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. Assertions that "twenty-four seconds should suffice, 24 hours gives one a safety margin" for solution deactivation of viruses without any substantiation would seem to run against this rule. If my posts are read for content, rather than putting words in my mouth, you might find that we agree more than you think. There's no reason to be hostile about it. Cheers, -AJHicks Chandler, AZ _______________________________________________ the OrchidGuide Digest (OGD) [EMAIL PROTECTED] http://lists.orchidguide.com/mailman/listinfo/orchids
