Halogens — Halogens are effective disinfectants when adequate cleaning has taken 

 place before their use. Unfortunately, the halogens are totally neutralized and made 

 ineffective by the presence of organic matter. These materials are more effective at an 

 acidic pH. Halogens are highly toxic for aquatic animals, so great care must be taken 

 never to discharge them into a watershed. If discharge into a watershed cannot be 

 avoided, the halogen should be neutralized with sodium thiosulfate at the rate of 5 

 moles of thiosulfate to 4 moles of halogen. 



Sodium Hypochlorite (chlorine) — Sodium hypochlorite (NaOCl) is commonly 

 available as household bleach. Chlorine solutions will decompose fairly rapidly when 

 they are exposed to heat or light. The stock solutions do tend to lose strength when 

 stored. Chlorine is highly sporicidal, and mixing it 50-50 with a solution that is half 

 alcohol and half water potentiates this effect. Chlorine-containing compounds are 

 highly corrosive. 



Calcium Hypochlorite — Calcium hypochlorite (Ca(OCl),), also called chlorinated 

 lime, is mentioned in 9 CFR part 71.10 (a)(3) as a permitted disinfectant. Chlorinated 

 lime (USP strength, 30-percent available chlorine) should be used in the proportion 

 of 1 pound to 3 gallons of water. 



Iodine — Iodine is less reactive than chlorine and dissolves readily in alcohol. 

 However, it is necessary to add potassium iodide to water to dissolve appreciable 

 levels of iodine. As a disinfectant, the spectrum oi' activity of iodine is similar to thai 

 of chlorine. Iodine is somewhat less effective against the nonenveloped viruses than 

 chlorine but is more effective than chlorine in the presence of organic matter. 



Peroxide Compounds — 



1. Hydrogen peroxide (H^OJ: When fresh, hydrogen peroxide is an effective 

 disinfection agent except in the presence of nonenveloped viruses or acid-fast 

 bacteria. The active agent in disinfection is the hydroxyl free radical ('OH), which 

 destroys micro-organisms through DNA strand breakage and the destruction 



of enzymes. The solutions of hydrogen peroxide commonly purchased will 

 decompose readiK, making it absolulch necessary to ensure that any solution lo 

 be used for disinfection is fresh. 



2. Peracetic acid (CH,C(0)OOH): Peracetic acid is an extremely shock-sensitive 

 explosive in il^ pure torni. It is supplied as a 40-percent solution in acetic acid, 

 which has an open-cup tlash point of 40.5 °C (105 °F) and will spontaneously 

 explode when heated to 1 10 °C (230 °F). Modern stabilized disinfectants using 

 peracetic acid are generally mixtures of peracetic acid, hydrogen peroxide, and 

 acetic acid. The level of active ingredient in mixed peracetic acid disinfectant 

 solutions is generally 0.25 percent or less. Peracetic acid alone or with hydrogen 

 peroxide is one of the high-level disinfectants cleared by FDA for processing 

 reusable medical and dental devices. 



7-10 



