Gerald E. McDonnell - Antisepsis, Disinfection, and Sterilization

Safety aspects include hazards in the use of the product, residues that remain on or in a treated product following application, environmental concerns, and reactivity on mixing with other agents. For this reason, biocides and biocidal products are usually provided with safety data sheets (e.g., material safety data sheets) that contain information regarding ingredients, hazards, first aid measures, personnel protection, stability and reactivity, toxicology, and ecological (e.g., bioaccumulation) concerns. For automated processes, these details should also be provided in equipment manuals and are often specified in various guidelines and standards. These safety aspects should be reviewed and considered prior to the use of a biocidal product or process. In many countries, the specific use of certain biocides may be restricted due to health and environmental concerns.

Finally, compatibility with the surface or product is important to ensure that unexpected damage does not occur. Compatibility may be defined as the suitability of a biocidal product or process to be used on a surface or in a solution without causing unacceptable interactions, damage, or other undesirable effects. It is for this reason that a restricted number of biocides are used on foods or on the skin (as antiseptics) (see chapter 4). A wider range of biocides are used on hard surfaces, but they also vary in compatibility (e.g., some heat-based processes cannot be used for temperature-sensitive surfaces or products). Other considerations will depend on the specific application and include reproducibility, ease of use, cycle or application time, cost, guidelines and standards (which are further considered in section 1.4.5), and specific regulatory requirements.

Various guidelines and standards are available that assist in the choice, use, testing, and validation of biocidal processes and products (examples of these are given in Table 1.25). They include international and country-specific requirements, many of which are mandatory for the use of the product or process in certain countries.

Unlike many therapeutic antimicrobials (such as antibiotics), most biocides are provided in formulation with other ingredients as products. Formulation may be defined as the combination of ingredients, including active (biocides) and inert ingredients, into a product for its intended use (e.g., cosmetics, antiseptics, and disinfectants). Inert (or excipient) ingredients include water, nonaqueous solvents, emulsifiers, chelating agents, and corrosion inhibitors. The functions of these various ingredients are summarized in Table 1.26.

TABLE 1.25 Examples of standards and guidelines for antisepsis, disinfection and sterilization

a ISO, International Standards Organization; EN, European Norm, from the CEN (European Committee for Standardization);APIC, Association for Professionals in Infection Control and Epidemiology (United States); EPA, U. S. Environmental Protection Agency; FDA, U. S. Food and Drug Administration, HC-HPFBI: Health Products and Food Branch Inspectorate of Health Canada; EC, European Commission;TGO-TGA, Therapeutic Goods Order-Therapeutic Goods Administration, Australia;WHO, World Health Organization.

The formulation of a biocide can be a complex task to ensure the optimization of antimicrobial efficacy, compatibility, required characteristics, and aesthetics of the final product. The first consideration is the choice of the biocide itself, which must have an optimal range of concentration, pH, temperature, solubility, stability, and spectrum of activity. It is also clear that the desired performance attributes of the product also need to be considered during its formulation (e.g., the effect of water quality if the product is diluted prior to use, compatibility with surfaces, and improved antimicrobial activity by synergy with other biocides or excipients). These considerations allow the choice of various formulation ingredients ( Table 1.26). The basic components of many formulations are water and other solvents (such as alcohols); although many biocides and other excipients are soluble (ionic or hydrophilic) in water, many are insoluble (hydrophobic). Biocides are therefore often mixed with emulsifiers, including soaps and detergents, to increase their solubility or dispersion in a formulation. Emulsifiers form micelles, which are aggregated units of surface-active molecules ( Fig. 1.26). Soaps are water-soluble salts or fatty acids, which are made by reactions of fats and/or oils with an alkali (e.g., sodium hydroxide). Detergents are mixtures of surfactants, which are defined as surface-active agents. Surfactant molecules act in low concentrations to change the properties of a liquid at its surface or interface with a surface. This increases the wettability of the liquid by breaking its surface tension, the force that holds the surface molecules together, and allowing it to spread over a surface better. Surfactants are further defined as nonionic (no charge), anionic (negatively charged), cationic (positively charged), and amphotheric (positively and negatively charged), and many possess antimicrobial activity (see section 3.16). Surfactants form micelles ( Fig. 1.26), which are useful for the solubilization, dispersion, or emulsification of incompatible materials, as well as aiding in cleaning processes by the removal and dispersion of hydrophobic soils from a surface.