Classes of biocides

Because the objective of this work was to assess the benefits of encapsulation, it was decided to opt for one structural class of biocide. The biocides selected for this purpose were based on the isothiazolinone structure. 2 Examples include 2-octyl-4-isothiazolin-3-one (OIT), 4,5-dichloro-2-octyl-4-isothiazolin-3-one (DCOIT), 5-chloro-2-methyl-4-isothiazolin-3-one (CIT) and 2-methyl-4-isothiazolin-3-one (MIT) (Figure 1). 

Biocides are formulated into the concentrates of products at anywhere between 20-25 times the end-use concentration. The preservative system must be soluble in the concentrate which may be a mixture of oil and water. The concentrate may then be stored anywhere between three months to one year. During this period of time, the biocide must remain active if it is to be efficacious when the product is used. There are many components in a metalworking fluid formulation that can deactivate certain types of biocides. For example, the presence of primary amines in many products rapidly deactivate isothiazolinone biocides, making this class of biocides unsuitable for use in the vast majority of metalworking fluid concentrates. 

Phenoxyethanol is one of the most commonly found actives of this class of biocides, (see Figure 7). 

The patent in question covers a class of biocides that are being marketed by Company A. Company B approaches Company A, the owner of the patent, in order to seek a licence to make and sell a compound, the structure of which is dominated by this patent. The decision to grant a licence is a purely commercial one. In this case the financial benefits to Company A are seen to outweigh the disadvantages. A licence is granted to Company B in return for 5% of the net sales income for the remaining lifetime of the patent. 

Biocides are used widely in industry. There are at least three main classes of industrial chemical biocides. The first class includes the oxidizing and bleaching agents, such as chlorine dioxide, hydrogen peroxide, and sodium hypochlorite. The oxidizing action may directly kill bacteria or fungi or weaken the cell walls so that they are more susceptible to other classes of biocides (see below). Sodium... 

These patterns in Total and Free ATP are as might be expected from what is known about the mechanism of action of these classes of biocides. 

In spite of high effectiveness of oxidizing biocides in cooling water systems, it is sometimes difficult to control problem organisms just with oxidizers alone. High reactivity and low persistence of most of oxidizers can leave some microorganisms unharmed, especially those that proliferate in biofilms. Therefore, the need exists in other classes of biocides that are more persistent and aimed at organisms less effected by oxidizers. 

In order to obtain the strong biocidal effect needed to avoid mould formation on the textile materials and to avoid decomposition of the textile materials, it is needed that active component diffuses out of the textile material to the micro-organism (e.g. by water through hydrolytic decomposition or dissolving). Various classes of biocidal agents that can provide this effect, are ... 

A classification by chemical type is given ia Table 1. It does not attempt to be either rigorous or complete. Clearly, some materials could appear ia more than one of these classifications, eg, polyethylene waxes [9002-88 ] can be classified ia both synthetic waxes and polyolefins, and fiuorosihcones ia sihcones and fiuoropolymers. The broad classes of release materials available are given ia the chemical class column, the principal types ia the chemical subdivision column, and one or two important selections ia the specific examples column. Many commercial products are difficult to place ia any classification scheme. Some are of proprietary composition and many are mixtures. For example, metallic soaps are often used ia combination with hydrocarbon waxes to produce finely dispersed suspensions. Many products also contain formulating aids such as solvents, emulsifiers, and biocides. 

Isothiazolinones are a class of broad-spectrum biocides used as preservatives in many household and industrial products. They are used in cosmetics and shampoos as a biocide to kill fungi and bacteria. Unlike the preservatives DMDM hydantoin and imidazolidinyl urea, also commonly used in these products, isothiazolinones do not release formaldehyde, to which some people are sensitive. On the other hand, some people are sensitive to isothiazolinones. 

Many of the standard works include only the word disinfection in their title yet deal with all classes of compounds and with a wide range of apphcatioa It is unrewarding to be too dogmatic about these terms many substances can function in both capacities depending upon their concentration and time of contact. A more general term, biocide, is now widely used to denote a chemical agent that, literally, kills microorganisms. 

It does have a number of draw backs. It has poor thermal stability (a property common to most formaldehyde release biocides) and, in some instances, may cause blackening of metalworking fluid concentrates if heated above 50°C for a period of time. Recently, this active ingredient was placed on Annex 1 of the Dangerous Substances Directive having been identified as a potential skin sensitiser. This means that formulations containing efficacious levels of this class of triazine in them would have to be labelled with R43 - may cause sensitisation by skin contact. This is unacceptable to many UK customers. As this material is only bactericidal, it needs to be co-formulated with a fungicide to provide complete protection for a product. 

Another class of formaldehyde release biocide are the oxizolidines. 

This material shares many of the advantages of the triazine biocides. They are relatively cheap, compatible with most formulations and provide a source of reserve alkalinity. In addition, at the time of writing, there are no requirements for labelling R43 with this class of material. It shares similar disadvantages to the triazines, possessing poor thermal stability. Oxizolidines also need to be co-formulated with a fungicide to provide complete protection for a product. 

Neutralizer Biocide Class Potential Action of Biocides... 

It seems likely that the future will see major developments in the use of metal complexes as bacteriocidal, viricidal, immunosuppressive, anti-arthritic and biocidal agents. One class of complexing agents that appears to have particular promise are the macrocyclic antibiotics, macrocyclic polyethers, polyamines and cryptates . In this group the ligand wraps around a metal ion to form a lipid-soluble complex... 

Kanazawa A, Ikeda T, Endo T (1993) Polymeric phosphonium salts as a novel class of cationic biocides. III. Immobilization of phosphonium salts by surface photografting and antibacterial activity of the surface-treated polymer films. J Poly Sci A Poly Chem 31 1467-1472... 

The basis and likely impact of this Directive have been described. Apart from some very brief comments, there has been no specific reference to surfactants. This is because the Directive covers any chemical that falls within the scope as described and whilst this will include many surfactants, it also includes many other types. Having said this, there is no reason to suppose that surfactants will fare better than any other class of chemicals. Also, as indicated at the beginning, this chapter describes the situation in autumn 2004 when much of the impact due to the transitional measures is still to be realised. This Directive is considered by many to be over the top control for this group of products. However, this is an inevitable consequence of biocidal products also being known as pesticides. Only time will tell whether this Directive will actually improve or increase the levels of risk to humans, animals or the environment. 

The word biocide encompasses a broad class of chemical agents and literally means an agent that destroys life. The United States Environmental Protection Agency defines the term biocide as follows ... 

A second class of industrial chemical biocides involves highly toxic organic chemicals. Subclasses of toxic biocides include thiazoles, thiocyanates, isothiazolins, cyanobutane, dithiocarbamate, thione, and bromo-compounds. As the names imply, many of the toxic biocides contain sulfur ( thio -). 

A third class of industrial chemical biocides consists of agents with the ability to inhibit biological film formation, also called surfactants . The term surfactant originates from the phrase surface active agent. Surfactants fall into four broad categories anionic (e.g., soaps, alkyl benzenesulfonates, alkyl sulfonates, alkyl phosphates), cationic (e.g., quaternary ammonium salts), nonionic (e.g., alkyl polyglycosides, alcohol ethoxylates, alkylphenol ethoxylates), and zwitterionic. 

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