Formaldehyde is a gas; glutaraldehyde is an oil at room temperature. Both are readily soluble in water. Formaldehyde and glutaraldehyde solutions are irritating or caustic to tissues, causing coagulation necrosis and protein precipitation; however, they have potent germicidal properties against all organisms, including spores. These solutions do not lose appreciable antimicrobial properties in the presence of organic matter and are noncorrosive to metals, paints, and fabric. Both are used as disinfectants. Because of the hazardous properties of formaldehyde sprays, premises where they are used as disinfectants (eg, piggeries) must be vacated for a long period of time after the spraying; therefore, researchers are actively seeking alternatives.
Formaldehyde at 4% concentration is used in foot baths to control Dichelobacter nodosus, a gram-negative, fastidious, anaerobic bacterium and the causative agent of ovine footrot.
Formalin contains 37% formaldehyde gas in aqueous solution with variable amounts of methyl alcohol to prevent polymerization. A 1%–10% solution of formaldehyde is commonly used as a disinfectant. Formalin at 10% concentration effectively fixes and preserves tissues and therefore is used to preserve organ samples for histopathologic examination and to preserve cadavers for dissection. However, it has adverse effects: exposure to formalin in medical and veterinary students causes eye and nose mucosal irritation; personnel with prolonged exposure to formalin have been reported to develop severe respiratory symptoms and migraines. Therefore, proper ventilation should be in place to decrease formalin vapor concentration in work spaces, and permanent staff should be provided with appropriate protective clothing.
Glutaral (glutaraldehyde), a 1%–2% alkaline solution (pH 7.5–8.5) in 70% isopropanol, is a more potent germicide than 4% formaldehyde, is effective against all microorganisms, including viruses and spores. It is often used to sterilize surgical and endoscopic instruments, as well as plastic and rubber apparatus. It is a known sensitizer, causing occupational contact dermatitis, as well as bronchial and laryngeal mucous membrane irritation.
Ortho-phthalaldehyde (OPA) is an aromatic aldehyde similar to glutaraldehyde, but with several potential advantages. Typical 0.55% solutions have excellent stability over a wide pH range (3–9), are less toxic and irritating to eyes and nasal passages, and have a barely perceptible odor. They are compatible with most materials, including components of dental instruments and flexible endoscopes. Pseudomonas aeruginosa strains exhibiting resistance to one or more than one antimicrobial family ("resistant or multiresistant" strains) also had a decreased susceptibility to OPA. It is not usually necessary to increase disinfection time for OPA to be effective, but for disinfection of endoscopes or instruments from patients colonized/infected by resistant/multiresistant P aeruginosa, it is better to use OPA for 15 minutes. OPA solutions act more quickly than glutaraldehyde against mycobacteria but have somewhat less sporicidal activity. A potential disadvantage of OPA is that it stains proteins (including unprotected skin) gray, so it must be handled with caution.
Sulfur dioxide, as a gaseous fumigant, is produced by burning sulfur in closed spaces. It is used mainly as a pesticide on edible plants after harvest and a disinfectant for food production and storage facilities. For maximal effect, the treated surface should be moist: the bactericidal effect is derived from sulfuric acid, which forms when the gas is dissolved in water. However, this reducing effect of the acid can also corrode metals, rot fabrics, and bleach dyes. Sulfur dioxide is an air pollutant that is harmful to living creatures.
