The purpose of disinfection is to eliminate microorganisms or at least reduce their numbers to a “satisfactory” level. Some disinfectants are effective in killing or inactivating specific types of microorganisms and others are effective against all types. It is therefore essential to know the identity of the target microorganisms to be destroyed. However, selection of disinfectants depends not only on their effectiveness, but also on their corrosiveness and other hazards related to their handling.
The types of chemicals used for disinfection of health-care waste are mostly aldehydes, chlorine compounds, ammonium salts, and phenolic compounds. The characteristics of these common types of disinfectant as chemical disinfectant are discussed below :
Formaldehyde (HCHO)
Application
Inactivating effect against all microorganisms, including bacteria, viruses, and bacterial spores; may be applied to dry, solid waste, in combination with steam at 80 0C. Contact time: 45 minutes.
Physical and chemical properties
Gas at ambient temperature; flammable and explosive in mixtures with air at concentrations of 7–73%; reactive at ambient temperature; polymerizes at temperatures below 80 0C. Formalin is a 37% solution of formaldehyde. Formaldehyde odour threshold: 0.1–1ppm.
Health hazards
WHO guideline value for the general public: 0.1ppm. WHO guideline value for occupational exposure: 1 ppm for 5 minutes, with no more than 8 peaks in one working period (of up to 8 hours). Irritant effects may be experienced at concentrations of 1–3ppm upwards; exposure to concentrations above 10ppm may result in severe irritation of eyes or respiratory tract. Occupational safety limit: 1ppm in the USA
Protective measures
Gloves and protective eye glasses should be worn during handling of formaldehyde to protect skin and eyes; in case of skin contact, the affected area should be rinsed abundantly with water.
Corrosiveness
Formalin is slightly corrosive to most metals except stainless steel and aluminium; it should be stored in stainless steel, aluminium, or polyethylene containers, in well ventilated, leakage-proof rooms.
Fire
Firefighters should wear breathing masks when tackling fires involving formaldehyde.
Comments
Formaldehyde is suitable for use as a chemical disinfectant only in situations in which a high level of chemical safety can be maintained.
Ethylene oxide (CH2OCH2)
Application
Inactivating effect against all microorganisms, including bacteria, viruses, and bacterial spores; disinfection of solid waste at temperatures of 37–55 0C, at 60–80% humidity, for 4–12 hours.
Physical and chemical properties
Gas at temperatures above 10 0C; flammable and explosive in mixtures with air at concentrations of 3% and above; very reactive at ambient temperature; soluble in water and most organic solvents. Odour threshold: 320–700ppm.
Health hazards
Liquid ethylene oxide and aqueous solutions are extremely irritant to skin and eyes; occupational safety limit: 1–5 ppm (depending on the country). Ethylene oxide has been classified as a human carcinogen by the International Agency for Research on Cancer; all precautions should therefore be taken to avoid inhalation of this compound during handling. NIOSH IDLH: 800ppm.
Protective measures
Gloves and protective eye glasses should be worn during handling of ethylene oxide to protect skin and eyes; in case of skin contact, the affected area should be rinsed abundantly with water; in case of eye contact, the eyes should be rinsed abundantly with water for at least 15 minutes, followed by medical examination; immediate hospital attention is needed in case of inhalation or ingestion; continuous monitoring of ethylene oxide should be performed.
Corrosiveness
Ethylene oxide is corrosive to rubber and plastics but not to metal; it is usually stored in pressurized metal containers, in liquid form, under high-pressure nitrogen gas.
Fire
Ethylene oxide fires are very difficult to stop; in case of fire, gas inflow should be stopped; CO2 or powder extinguishers should be used; firefighters should wear protective masks.
Comments
The use of ethylene oxide is not recommended because of significant related health hazards.
Glutaraldehyde (CHO-(CH2)3-CHO)
Application
Active against both bacteria and parasite eggs. Available in 25–50% aqueous solutions; should be used as 2% aqueous solution with acetate buffer. Contact times: 5 minutes for disinfection of medical equipment; 10 hours to kill spores. For waste, operating parameters should be adjusted on the basis of bacteriological tests.
Physical and chemical properties
Liquid; very reactive; non-flammable. Addition of methanol allows for long-term conservation.
Health hazards
Concentrated solutions are irritant to eyes and skin; occupational safety limit depends on the country (e.g. 0.2ppm or 0.7mg/m3 in France
Protective measures
Gloves and protective eye glasses should be worn during handling of glutaraldehyde to protect skin and eyes; in case of skin contact the affected area should be rinsed abundantly with water; in case of eye contact, the eyes should be rinsed abundantly with water for at least 15 minutes, followed by medical examination.
Corrosiveness
Aqueous solutions of glutaraldehyde are corrosive to most metals; usually stored in stainless steel containers, steel containers lined with phenolic resins, or reinforced polyethylene containers, in well ventilated, leakage-proof rooms.
Comments
Glutaraldehyde is suitable for use as a chemical disinfectant only in situations in which a high level of chemical safety can be maintained. Glutaraldehyde waste should never be discharged in sewers; it may be neutralized through careful addition of ammonia or sodium bisulfite; it may also be incinerated after mixing with a flammable solvent.
Sodium hypochlorite (NaOCl)
Application
Active against most bacteria, viruses, and spores; not effective for disinfection of liquids with high organic content such as blood or stools; widely used for treatment of wastewater. For waste, operating parameters should be adjusted on the basis of bacteriological tests.
Physical and chemical properties
Available as aqueous solution with 2–12% of active chlorine; at ambient temperature slowly decomposes into sodium chlorate, sodium chloride, and oxygen; solutions of low concentration are more stable; solutions should be protected from light which accelerates decomposition; reacts with acids to produce hazardous chlorine gas.
Health hazards
Irritant to skin, eyes, and respiratory tract; toxic.
Protective measures
Gloves and protective eye glasses should be worn during handling of sodium hypochlorite to protect skin and eyes; in case of eye contact, the eyes should be rinsed abundantly with water.
Corrosiveness
Aqueous solutions are corrosive to metals; usually stored in plastic containers in well ventilated, dark, and leakage-proof rooms; should be stored separately from acids.
Comments
Sodium hypochlorite may be widely used because of relatively mild health hazards. Unused solutions should be reduced with sodium bisulfite or sodium thiosulfate and neutralized with acids before discharge into sewers. Large quantities of concentrated solutions should be treated as hazardous chemical waste.
Chlorine dioxide (ClO2)
Application
Active against most bacteria, viruses, and spores; widely used, for instance in drinking-water preparation, sanitation, and wastewater treatment.
Physical and chemical properties
Reddish-yellow gas at ambient temperature; explosion limit: >10% in air; will react with water or steam to produce corrosive fumes of hydrochloric acid.
Health hazards
Irritant to skin, eyes, and respiratory tract; toxic. NIOSH IDLH: 5ppm.
Protective measures
In case of eye contact, eyes should be rinsed abundantly with water; contaminated areas of the body should be washed with soap and water.
Corrosiveness
Containers of chlorine dioxide should be stored in well ventilated and leakage-proof rooms.
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