8.2.2 Chlorine compounds

Chlorine is a broad-spectrum germicide and is the recommended general all-purpose laboratory disinfectant.  Chlorine is effective against bacteria, mycobacteria, viruses and fungal spores.  However, not all bacterial spores are killed by chlorine and the amount of available chlorine must be considered when preparing the disinfectant.  A concentration of 5,000 ppm (parts per million) available chlorine is recommended as an all-purpose disinfectant.  A higher concentration, near 10,000 ppm available chlorine, is recommended for biohazardous spills, emergency situations involving viruses and in the presence of large amounts of organic matter (protein, including dirt).  

Sodium hypochlorite (NaOCl), as an aqueous solution, is sold as bleach.  Laundry bleach contains 5.25 percent available chlorine; solutions of 10 percent or 20 percent will yield concentrations of 5,000 ppm and 10,000 ppm available chlorine, respectively.  The activity of chlorine, especially as bleach, is reduced in the presence of protein.  Solutions receiving material containing high levels of organic matter several times a day should be replaced daily, while less frequently used solutions can last for one week.  Furthermore, low levels of chlorine gas are naturally released from stored solutions of chlorine and reduce the germicidal activity.  

Note:  Chlorine gas is highly toxic and therefore bleach should not be mixed with acids which would cause the release of chlorine gas.  Additionally, chlorine is highly alkaline and is corrosive to metal.  By-products of chlorine can be harmful to humans and the environment, therefore chlorine containing compounds should not be used indiscriminately.

Chloramines release chlorine at slower rates than hypochlorites and therefore higher concentrations are required to achieve equivalent activity to those of hypochlorites.  However, chloramine solutions are virtually odour-free and are not inactivated by organic matter to the same extent as hypochlorites.  Concentrations of 20,000ppm available chlorine are recommended for both “clean” and “dirty” situations.