Rev. sci. tech. Off. int. Epiz., 1995,14 (1), 57-74

Chemicals used as disinfectants: active ingredients and enhancing additives

D.J. JEFFREY *

Summary: Active ingredients used in microbiocidal products in the European Union constitute some 250 chemical entities. Approximately 100 of these chemicals are commonly used in disinfectant products. The majority of these substances may be classified into distinct chemical groupings. A brief review of the chemical, physical and microbiological properties of each group is given, together with some indications of additives which may be used to enhance their properties, and factors which may detract from them. Some indications of usage areas are given.

KEYWORDS: Additives - Chemicals - Disinfection - Microbicidals.

INTRODUCTION

As a result of the proposed E u r o p e a n Union Biocidal Products Direct ive, representat ives of the disinfectants industry in E u r o p e were asked to identify the number of active components used in products which were likely to come under the scope of the Directive. Some 250 chemical entities were thus identified (8). Not all these actives are in common use: some have particular applications for a specific purpose (so-called 'n iche ' products) , while others have applications as preservatives, water biocides, 'slimicides', etc., and are not generally used in disinfectant formulations.

The list contains a wide range of chemicals, from simple inorganic molecules (e.g. sodium hydroxide) to relatively complicated molecules (e.g. polymerised quaternary ammonium compounds [QACs] or substituted isothiozolones).

At first thought, one might wonder why such a plethora of active substances exists, if they all kill microorganisms. However, on examination, the reason becomes obvious. The physical and chemical properties of disinfectants can limit the choice for a particular application. It would not be reasonable to use a sodium hydroxide solution on surfaces containing tin, zinc or aluminium, as the solution would react with and corrode such materials. It would be unwise to use hydrochloric acid on mild steel or iron for similar reasons. Oxidising agents cannot be used in the presence of reducing substances, which would neutralise their effect. Surface-active properties may be required for some purposes but not for others, and a number of additional properties (tainting, staining, toxicity, etc.) must also be taken into account, as they could render an active component unsuitable.

In addition to physical and chemical properties, the microbiological attributes of the active substance must also be considered. Few active substances are able to kill all the types of microorganisms (and their spores) which are likely to be encountered, and these substances are not suitable in all applications for various reasons.

* Jeyes Limited, Brunei Way, Thetford, Norfolk IP241HF, United Kingdom.

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Most chemical actives are not effective against bacterial spores, and most are only mildly effective against mycobacteria or lipophobic viruses. Some actives are relatively ineffective against fungi, while others are insufficiently effective against Pseudomonas spp. Not all bacterial or fungal species are equally susceptible to a given concentration of a given product, and even different strains of the same species of bacteria, fungus or virus may vary in resistance.

For the above reasons, a large number of active chemicals are now commercially available. It should be possible to choose at least one active substance (or a combination of actives) to obtain the best results in any given situation.

Most of the active chemicals on the above-mentioned list (8) fall into particular chemical groups, and most are well established. Only approximately one-third of the available actives are commonly used in the veterinary field.

Active disinfectant substances may be classified into the following groups:

- QACs - phenols - halogen-releasing compounds - halogenated phenols - aldehydes - biguanides and polymeric biguanides - amphoterics - iodine-based compounds - alcohols - acids - peroxygen-based compounds - alkalis - miscellaneous.

Details of the active ingredients are presented below, together with a discussion of potential enhancing additives.

All QACs have the basic structure shown in Figure 1.

R1 is nearly always a C 8-18 alkyl group. R 2 may be a long- or short-chain alkyl group or an aryl group. R 3 and R 4 are usually short-chain alkyl groups. X is usually a chloride ion but may be a bromide ion.

A few Q A C s have a pyridinium ion with long-chain alkyl groups and some are polymerised. The structure of most common types of QACs is given in Figure 2.

QUATERNARY AMMONIUM COMPOUNDS

x-

FlG. 1

Basic structure of quaternary ammonium compounds

59

C H 3

I C n H 2 n + i - N + — CH 3

CH, alkyltrimethyl ammonium bromide

Br

C H ,

CnH: n n2n+1 V — C n H n + 1 Cl

C H ,

• 0 — (CH6)2

C H 3

I

dialkyldimethyl ammonium chloride

(CH2)n CH3 Br

CH3

domiphen bromide

CH,

> - C H 2 l\T — C H 2 - C H 2 0 - CH - C H 2 0 - < l

C H 3

benzethonium chloride

CH3 CH3

i i — C — C H 2 — C - C H 2 CH 2 0

I I CH3 CH3

C H 3

f - C H 2 — N + C n H 2 n + 1

C H 3

benzalkonium chloride

c r >— N* — ( C H 2 ) 1 5 — C H 3 Cl H 20

cetylpyridinium chloride

C H 3

c n H 2 n + 1 — r — C H 3

I C H 2

I ^ Cl

Cl alkyI(dichlorophenyl)methyldimethyI chloride

CHoCI C H ,

— 0 — C H 2 — C H 2 — N + — C H 2 C H 2 — N + — C H 2 — C H 2 —

C H 3 C H 3

polymeric quaternary ammonium compound

FIG. 2

Chemical structure of the common types of quaternary ammonium compounds

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All QACs are cationic. The first use of these compounds dates back to 1916 (6) but not until 1935, when the chemistry had been further developed, did QACs begin to enter common use (3). Since then, QACs have been widely used in disinfectants, antiseptics, pharmaceuticals and cosmetics.

Since 1935, it has been shown that QACs are much more effective in preventing the growth of bacteria than in killing them. QACs have been shown to be far more active against Gram-posit ive bacteria than against Gram-negative bacteria, to have more bactericidal than fungicidal activity, and to be effective against lipophilic viruses but not against lipophobic viruses. QACs may be sporostatic (7), but they are not sporicidal and are relatively ineffective against mycobacteria (9). Notwithstanding the above comments, the bactericidal activity of QACs against most bacteria is sufficient for them to have found many applications.

Used alone, QACs possess a certain degree of surface activity, but they are usually formulated with compatible non-ionic detergents to increase detergency. The activity of QACs declines in the presence of hard water, and they are usually formulated in combination with chelating agents (e.g. the salts of ethylenediaminetetraacetic acid [EDTA]) or chemicals such as sodium citrate or t r ipolyphosphate (which remove calcium and magnesium ions from the water). The activity of QACs is greatly reduced in the presence of soiling matter, and it is therefore best to clean away heavy soiling before using these compounds. QACs are not compatible with soaps or ordinary anionic detergents; if these are used for cleaning, they must be rinsed off before applying QACs or the disinfectants will lose much of their activity. QACs are more effective in alkaline conditions than in acid conditions, and a number of Q A C formulations contain alkalis, such as sodium carbonate or metasilicate. Some care must be taken in composing such formulations, as QACs can lose some of their activity if the ratio of the various constituents is incorrect.

QACs are sometimes formulated in combination with other actives (notably Chlorhexidine or polymeric biguanides) to increase their efficacy against some Gram-negative species, or they may be formulated in combination with glutaraldehyde to kill the whole spectrum of microorganisms more rapidly than glutaraldehyde alone.

Q A C formulations (both alone and in combination with other substances) have been widely used in veterinary disinfectants.

The action of these formulations is reasonably rapid, they have a high concentration exponent, and a rise in temperature increases their activity. In use dilutions, QACs are usually non-corrosive to surfaces, but strong concentrations can corrode mild steel or iron.

A wide range of QAC-based products exists and selection is difficult. The literature supplied by manufacturers should be consulted, but laboratory tests on these formulations give highly variable results, and the only way to prove their efficacy in a given situation is to assess the products in practice.

PHENOLS

Phenols are among the oldest established active disinfectant substances. Originally derived from coal tar, they were extensively used in the early 20th century and still play a major role in the disinfectant armoury today. In the United Kingdom and Ireland, over 30% of disinfectants used in veterinary applications are based on phenols . However, in Germany, only 7% of veterinary disinfectants are phenolic (4). All these substances are chemically based on the phenol molecule (Fig. 3).

Chlorinated phenols

OH OH

CH, CH, CH,

CI

CH3

CI CI 4-chloro-3,5-metaxylenol (PCMX) 2,4-dichlorometaxylenol (DCMX)

OH OH

-CH,-

CI CI 4-chloro-2-o-phenylphenol (MCOPP) 2-benzyl-4-chlorophenol (OBPCP)

PCMX: parachlorometaxylenol

FIG. 3

Phenols and chlorinated phenols

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Phenols

phenol o-cresol m-cresol p-cresol

2,4-xylenol 2,6-xylenol 3,4-xylenol 3,5-xylenol

o-ethylphenol o-phenylphenol

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Phenol itself is rarely used now, as it is highly toxic and corrosive, but the higher homologues (cresols, xylenols and ethylphenols) are still used. Phenols have a wide spectrum of activity against bacteria, viruses, fungi and mycobacteria , while their sporicidal activity is minimal. Phenols have poor surface activity and have therefore traditionally been formulated in soap solutions to increase their penetrative power. The choice of soaps which may be used is very limited: the sodium or potassium salts of castor oil, linseed oil or resin acids have generally been used for this purpose. Soaps based on tallow, tall oil or oleic acid markedly decrease the activity of phenols.

Phenolic disinfectants are divided into three categories, as described below.

Clear soluble phenols

'Clear solubles' are so called as they yield a clear, opalescent solution in distilled water. They essentially consist of cresol, xylenol, o-ethylphenol (alone or in combination) dissolved (20-30%) in a liquid soap. Ethyl alcohols or glycols may also be included in the formula. Such products are effective under conditions of heavy soiling and are therefore among the products of choice where such conditions exist. Clear solubles are incompatible with acids or strong alkalis. Acids break down the soap, and alkalis convert the phenol to the phenate ion, which is less effective than the phenol molecule and can cause resinification, resulting in loss of activity. Products based on cresol are corrosive to skin, but those based on xylenols or higher phenols are less corrosive. Clear solubles have a low concentrat ion exponent and are almost as bactericidal as bacteriostat ic; they must therefore be used at the recommended concentration or their activity will be lost.

White fluid phenols

'White fluid' phenols are produced by making a colloidal solution of a low boiling-point tar acid fraction and so-called 'neut ra l ' oil (a complex eutectic mixture of naphthalene, dimethylnaphthalenes, acenaphthene and other aromatic hydrocarbons) in water. This is usually made in a colloid mill or in a homogeniser, but ultrasonics can also be used. A small amount of soap is usually added and the emulsion is held together by a colloid protectant (usually glue or casein). White fluids have a distinct advantage over nearly all other types of disinfectant in that they can be diluted with seawater or brackish water without breaking down or losing their activity (nearly all the navies of the world formerly used these disinfectants). They are effective in conditions of heavy soiling and have a wide spectrum of microbicidal activity. White fluid phenols have been used extensively for terminal disinfection in farm buildings. However, they are toxic and have a tarry odour, and if the emulsion breaks down they can leave tarry deposits.

Black fluid phenols

'Black fluid' phenols are based on a tar fraction of higher boiling-point than that used for the white fluids. This tar fraction is a complex mixture of higher homologues of phenol , naphthols , indanols, anthracols, etc. It is quite insoluble in water and must therefore be solubilised in 'neutral ' oil. This mixture is then solubilised with a soap solution or an ethoxylated castor oil sulphonate; glycerols or glycols may also be added. The high boiling-point tar acids used in these products do not have the same wide spectrum of activity as those used in the white fluids. These products are effective against a wide range of Gram-negative and Gram-positive bacteria, but are relatively ineffective against Pseudomonas spp. and mycobacteria, and are not effective against lipophobic viruses. However, their level of fungicidal activity is quite high.

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Black fluid phenol products are effective in conditions of heavy soiling. They form white emulsions when diluted and have a tarry odour. By formulating tar acids in combination with sulphonic acids and acetic acid, highly bactericidal, fungicidal and virucidal products have been formulated for farm use. Formulat ions have also been developed using triethanolaminedodecylbenzene sulphonate as an emulsifier.

One phenol worthy of special mention is o-phenylphenol. This can be incorporated into clear soluble products and is quite often used in combination with halogenated phenols to enhance their activity. It is less toxic and less corrosive than most other phenols.

Formulating with phenols requires great care, as the activity of the formulation relies on both oil/water partition and micelle concentration.

HALOGEN-RELEASING COMPOUNDS

Sodium hypochlorite solutions are probably the best known of the halogen-releasing compounds and are among the oldest and most common of all disinfectants. They are extremely effective against all types of microorganisms (Table I) but lose much of their activity in the presence of soiling. Sodium hypochlorite solutions do not wet surfaces effectively and have consequently been formulated with various detergents (e.g. amine oxides, soaps, alkane sulphonates and ether sulphates) to enhance their detergency. These additions do not affect the microbicidal activity of these products.

The advantages of sodium hypochlorite solutions over other disinfectants include low toxicity at use concentrations, ease of use and relatively low cost. Concentrated solutions are corrosive to skin, metals and other materials. These products are usually formulated with a little sodium hydroxide to enhance stability; otherwise, stability is greatly affected by trace metals (particularly copper, nickel and chromium), which catalyse the rapid breakdown to salt and water. These solutions should never be mixed with acids, as the resultant reaction releases toxic chlorine gas.

For many years, sodium hypochlorite solutions have been used in water treatment, in dairying operations, in the food industry and in the home.

As the stability of hypochlorite solutions is exponentially related to concentration, strong solutions lose more of their activity in a given time than weak solutions. Thus, in six to nine months under normal storage conditions, a 10% solution would decrease to 5%; whereas a 5 % solution would fall to 2 .5%. With increasing quality assessment at manufacture, the stability of hypochlorite solutions has improved in recent years and it is possible to obtain 5 % solutions which only decay to 4.0% in nine months under normal storage conditions.

Potassium hypochlor i te has proper t ies similar to those of sodium hypochlori te . Neither of these chemicals is stable in solid form, whereas lithium hypochlorite and calcium hypochlori te are stable as solids, and may therefore be used to formulate powders. Other powdered compounds which release hypochlorite ions in solution are trichloroisocyanuric acid (giving 90% active chlorine), sodium dichloroisocyanurate (55-60%), dichlorodimethylhydantoin (55%), chlor.amine-T, halozone, N-chloro-succinimide (40%) and chlorinated trisodium phosphate (10%). Trichloroisocyanuric acid, sodium dichloroisocyanurate and calcium hypochlorite have all been formulated into tablets to give concentrated solutions of active chlorine in solution. Dichloro-

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dimethylhydantoin, N-chlorosuccinimide and chloramine-T are less soluble but have also been incorporated into powder formulations with detergents and have all been used for water treatment. Chlorinated trisodium phosphate has been incorporated into various detergent sanitisers; it has the grease-emulsifying proper t ies of t r isodium phosphate , with the antimicrobial activity of active chlorine. Any tablet or powder formulations containing this substance must be kept dry, as chlorine loses activity very rapidly when wet. All these chemicals are extremely reactive, and care must be taken in formulating with them. Non-ionic detergents generally react with these substances, but powdered anionic detergents (e.g. sodium dodecylbenzenesulphonate or a lkane sulphonate) are suitable.

Al though bromine is more antimicrobially active than chlorine, few bromine-releasing products have found a place in the disinfectant marke t to da te . Bromochlorodimethylhydanto in has been used for water t rea tment , and sodium bromide is commonly added in powdered sanitiser formulations containing active chlorine products, as the chlorine releases bromine in solution. A number of powders which can release chlorine dioxide have recently appeared on the market . Chlorine dioxide is said to have greater antimicrobial activity than hypochlorite and to be more environmentally friendly. These powders usually contain sodium chlorate or sodium chlorite and an acid which releases chlorine dioxide in situ.

HALOGENATED PHENOLS

As suggested by the name, in halogenated phenols one or more of the hydrogen atoms in the phenol molecule has been replaced by a halogen atom, usually chlorine or bromine. Halogenat ion of the molecule significantly alters the phenolic propert ies. These substances are less soluble, less corrosive and less toxic than the corresponding phenol; they have a higher activity against both Gram-posit ive and Gram-negat ive bacteria but are less effective in the presence of soiling matter. Halogenated phenols are generally formulated by dissolving in pine oil or other terpene hydrocarbons or alcohols and then emulsifying the resultant solutions with liquid soap. These actives can be formulated with some anionic detergents , but most anionic, non-ionic and cationic detergents reduce their activity.

Formulations containing parachlorometaxylenol (PCMX), 2,4-dichlorometaxylenol (DCMX) and o-benzyl-p-chlorophenol (OBPCP) (see Fig. 3) have been widely used as antiseptics. Together with monochlorophenylphenol, halogenated phenols have also been used in pine disinfectants, sometimes in combination with o-phenylphenol. Some have been incorporated into clear soluble phenolic disinfectants to enhance their activity. Halogenated phenols have an intense odour and can be very tainting; they should therefore not be used near food.

The activity of these substances against Pseudomonas spp. is increased by including chelating agents, such as E D T A or ethyleneglycoltetraacetic acid ( E G T A ) , in the formulation.

Increasing the degree of substitution of halogen in the molecule decreases solubility and generally decreases bactericidal activity, while increasing fungicidal activity.

Products containing halogenated phenols have not found wide use in veterinary applications, although they have been used as fogging sprays.

67

The halogenated bisphenols, particularly trichlorsan, have found applications in antibacterial hand soap formulations. They are very effective against Gram-positive bacteria but much less effective against Gram-negative bacteria.

ALDEHYDES

Some aldehydes have a wide spectrum of activity against bacter ia , fungi, mycobacteria, spores and viruses. Formaldehyde is the best known, and certainly the most established, of these substances. It has been used extensively in liquid prepara t ions , part icularly in Germany, Aust r ia and Switzerland; according to Haskoning (4), 30% of veterinary disinfectants used in Germany are aldehydic.

Formaldehyde has been used extensively in liquid prepara t ions in the Uni ted Kingdom for disinfection of chemical toilets. It has also been used as a fumigant, by boiling formalin solutions, reacting formalin with potassium permanganate or heating paraformaldehyde. High relat ive humidity is requi red for opt imum efficacy. Formaldehyde is not very penetrative.

Glutaraldehyde is said to be at least three times as active as formaldehyde, but lacks chemical stability in strong solution. It has been extensively used in solutions for the chemical steril isation of sensitive medical ins t ruments (e.g. endoscopes) . Glyoxaldehyde, glycidaldehyde and succindialdeyhyde have also been used in some preparations but are generally less effective than glutaraldehyde.

All the above-mentioned aldehydes can work in conditions of heavy soiling; all act rather slowly with a low concentrat ion exponent. Aldehydes oxidise slowly and are relatively reactive with other chemicals. Care must therefore be taken in formulating with aldehydes to obviate these problems. Care must also be taken in using these substances, as they are potential respiratory sensitisers.

In more recent times, aldehydes have been formulated in conjunction with QACs or amphoterics to achieve a synergistic effect, obtaining more rapid action and higher activity over a wider spectrum.

BIGUANIDES AND POLYMERIC BIGUANIDES

This section details the propert ies of alexidine, Chlorhexidine and the polymeric biguanides.

All these actives have a broad spectrum of ant ibacter ial activity, but they have limited fungicidal and virucidal properties. They function across a limited pH: 5-7 in the case of alexidine and Chlorhexidine, and 5-10 for the polymeric biguanides. They are all incompatible with anionic detergents and inorganic anionic compounds.

Chlorhexidine itself is insoluble in water, but Chlorhexidine gluconate is quite soluble and is the salt most generally used. Chlorhexidine gluconate is much more bacteriostatic than bactericidal; it has virucidal properties but is not sporicidal or mycobactericidal. It has been formulated in aqueous or alcoholic solutions for pre-operative skin treatment and has been used in conjunction with quaternary ammonium compounds in antiseptic and detergent sanitiser formulations.

Alexidine has mainly been used in oral antiseptics.

68

Polymerie biguanides have been used extensively in combination with either QACs or non-ionic detergents in the brewing and food industries. They have a wide spectrum of activity, and both polymeric biguanides and Chlorhexidine are generally more effective against Pseudomonas spp. than QACs, although resistance to Chlorhexidine has been reported. These substances cannot be formulated with alkalis.

AMPHOTERIC COMPOUNDS

Amphote r i c compounds have both positive and negative charges in the same molecule (so-called 'switterions'). They can thus be formulated with either anionic or cationic substances. In the 1950s, some amphoteric detergents were discovered to have antimicrobial properties. Of these, one particular group based on alkyl betaines was commercially exploited. Subsequently, increasing the number of amine nitrogens in the molecule was found to increase the activity of these detergents. Amphoteric compounds are less active than most QACs, but the spectrum of microbicidal activity is less biased towards Gram-positive organisms. Amphoterics have good detergency in their own right and are more easily rinsed off than most quaternaries. They have found extensive use in the dairy and pharmaceutical industries.

Amphoter ics cannot withstand heavy soiling, their virucidal activity is limited to lipophilic viruses and they are ineffective against spores, although they are reported to have some mycobactericidal activity (5). These substances have been formulated in conjunction with flutaraldehyde and formaldehyde to give products with detergency and a wider spectrum of activity.

Amphoterics can possibly be used to enhance the activity of some phenols (E. Reeve, personal communication).

IODINE-BASED COMPOUNDS

Iodine itself is not very soluble and is generally too toxic, corrosive and staining for use as a microbicidal active, although it is among the most active disinfectant substances known.

In the early 20th century, iodine was used extensively as an antiseptic, in solutions in which the iodine was dissolved in alcohol and potassium iodide. These t inctures of iodine were found to be too irritative to skin and mostly fell into disuse. Iodine was discovered to be reactive with neutral polymers, particularly polyvinyl pyrrolidine, to yield a product which has found extensive use as a surgical hand-wash and antiseptic. Iodine was also found to react with ethoxylated surfactants to produce iodophors . These iodophors are usually stabilised with either acids or acidic buffers. They have an extremely wide spectrum of activity against bacteria, spores, mycobacteria, fungi and viruses, and have found extensive use in the veterinary field.

Iodophors have a low temperature coefficient compared to most other products, and therefore work almost equally well at low and high temperatures.

Iodophors cannot be mixed with other products, nor can they be used in alkaline conditions. They can cause staining if not used properly.

69

ALCOHOLS

Although some alcohols have been extensively used as skin disinfectants, they are not particularly active. Ethyl alcohol, isopropyl alcohol and M-propyl alcohol are most active at 70% concentrat ion and retain some activity down to approximately 10%. However, alcohols have found extensive use as solvents and have been used in formulations of disinfectants in combination with phenols, halogenated phenols, QACs and Chlorhexidine. Alcohols have the advantage of evaporating quickly and leaving no residues; they have therefore been used as spray disinfectants in the food industry.

Terpene alcohols also have some germicidal proper t ies and have been used in combination with halogenated phenols in so-called 'pine fluids'.

Phenoxyethanol and phenylethyl alcohol have also been used in formulations to increase activity against Pseudomonas spp.

ACIDS

Inorganic acids (e.g. nitric, hydrochloric, sulphuric, phosphoric and sulphamic acids) are used as cleaners for removing limescale, milk stone, etc. They all have microbicidal properties due to the low p H levels, but are generally slow-acting. Inorganic acids are efficient cleaners, but have strict l imitations due to corrosiveness to both skin and materials.

In addit ion, many organic acids (e.g. formic, citric, lactic, mallic, glutaric and propionic acids) have been used in disinfectant formulations to enhance virucidal and fungicidal proper t ies . Their activity is greatly enhanced in the presence of anionic detergents of the sulphonate or ether sulphate type, and this property has been used in a number of sanitiser formulations; these formulations usually use hydratropes, such as substituted alkylmonocarboxylic acids.

Acetic acid and benzoic acid work through the action of the undissociated molecule. Acetic acid has an acrid smell but has been used as a disinfectant in lavatory cleaners and in combination with some phenolic formulations; it is a component part of peracetic acid. Benzoic acid is most often used as a preservative in the soft drinks industry.

All acids are slow-acting and have a low concentration exponent.

PEROXYGEN-BASED COMPOUNDS

Hydrogen peroxide has good ant ibacter ia l proper t ies and has been used in formulations at 5-20%. It is not very fungicidal, and the organisms which contain catalase are resistant to low concentra t ions . Hydrogen peroxide is a very reactive material, is not very stable and is destroyed by alkalis. To increase stability, the p H is adjusted to approximately 5 and phosphonates are added. Hydrogen peroxide has found intensive use in sterilising cardboard packaging used for milk. The breakdown products are water and oxygen, thus rendering hydrogen peroxide particularly suitable for this purpose.

Of the o ther peroxygen-based products , peracet ic acid has found use in food processing and dairying. It is presented in a mixture with acetic acid and hydrogen

70

peroxide . Peracet ic acid has an acrid odour but kills all types of microorganisms, including spores, and is active in the presence of soiling matter.

Many other peroxygen compounds (e.g. pe rcarbona te per lac ta te , persuccinate perbenzonate and pervalerate) have microbicidal properties, but they are generally unstable and have found little use in the disinfectant industry.

Sodium and potassium monopersulphates have the property of producing chlorine from salt solutions and peroxide in acid solution. This proper ty has been used in powdered disinfectant formulations, one of which has been extensively used for veterinary disinfection.

Sodium metaperiodate has been added to some formulations to increase activity, as it has chelating powers for some heavy metals.

ALKALIS

Sodium and potassium hydroxide have been extensively used for their cleaning properties in the food and dairy industries. They have microbicidal properties as well as good grease- and debris-removing properties, but their activity is slow. The activity of these chemicals is much increased by raising the t empera tu re and using high concentrat ions. Sodium and potassium hydroxide are very corrosive and must be handled with care. They are used extensively in 'cleaning-in-place' systems, usually followed by an acid rinse.

Quicklime (calcium oxide) has often been used to disinfect animal corpses. Sodium carbonate and sodium metasilicate have little microbicidal activity but have been used in formulations with other actives to increase their grease-removing properties, enhance penetration and raise the pH.

MISCELLANEOUS MICROBICIDES

The list of miscellaneous microbicides is long, but it is probably worth mentioning a few of these chemicals. Products for the hygiene of hands have been formulated using 1,3-propanediol, 2-bromo-2-nitro, 3,4,4'-trichlorocarbanilide and 3',4' ,5-trichloro-salicylanilide, while the hydroxybenzoates have been widely used as preservatives and have found some application as additives to disinfectant formulations.

In the vapour phase, ethylene oxide and propylene oxide have been extensively used, and ozone has been used in water treatment.

CONCLUSION

The formulator of microbicidal products is therefore faced with a wide choice, while not all products are suitable for all applications. When deciding which formulation to use for a particular application, the user must first define the conditions of use and then ask some of the following questions:

- Is heavy soiling present? - If cleaning is to be performed first, is the product compatible with the cleaning agent?

71

- Is hard water to be used? - Will tainting pose problems? - How quickly should the required product work? - What is the working temperature? - Is corrosion or staining likely to be a problem? - What is the required price range?

The user should then select a few formulations which satisfy the criteria, read the literature supplied by the manufacturer and then make a choice.

The types of product in use in the United Kingdom for particular applications in the veterinary area are listed in the Appendix.

* *

PRODUITS DÉSINFECTANTS CHIMIQUES : ÉLÉMENTS ACTIFS ET ADJUVANTS. - D.J. Jeffrey.

Résumé : Les composants des produits microbicides utilisés dans l'Union européenne constituent quelque 250 entités chimiques. Une centaine de celles-ci environ sont couramment utilisées comme produits désinfectants. La plupart de ces substances peuvent être classées en groupes chimiques distincts. L'auteur passe brièvement en revue les propriétés chimiques, physiques et microbiologiques de chaque groupe. Il donne quelques indications concernant les additifs qui peuvent être utilisés pour renforcer leur activité ainsi que sur les facteurs qui risquent de réduire cette activité. Il précise également les indications d'emploi de ces différentes groupes.

MOTS-CLÉS : Additifs - Désinfection - Microbicides - Produits chimiques.

* * *

PRODUCTOS DESINFECTANTES QUÍMICOS: ELEMENTOS ACTIVOS Y ADYUVANTES. - D.J. Jeffrey.

Resumen: Los componentes de los productos microbicidas usados en la Unión Europea constituyen alrededor de 250 entidades químicas. Unas cien de éstas se usan corrientemente como productos desinfectantes. La mayoría de estas sustancias pueden clasificarse en grupos químicos distintos. El autor hace una breve enumeración de las propiedades químicas, físicas y microbiológicas de cada grupo. Da también algunas indicaciones acerca de los aditivos que se pueden utilizar para reforzar su actividad así como sobre los factores capaces de reducir esta actividad. Ofrece por último indicaciones para el uso de cada uno de los grupos.

PALABRAS CLAVE: Aditivos - Desinfección - Microbicidas - Productos químicos.

* *

72

App

endi

x

Type

s of

pro

duct

in u

se in

the

Uni

ted

Kin

gdom

for

part

icul

ar v

eter

inar

y ap

plic

atio

ns

Reg

ulat

ory

App

licat

ion

area

E

ffic

acy

Elle

rt o

t U

se

Cor

rosi

on T

ox

ico

log

ica

l cod

es

of

Stan

dard

test

s Ty

pica

l pr

oduc

ts

soili

ng

tem

pera

ture

pr

oper

ties

prac

tice

Cattl

e fa

rmin

g/dair

y Ho

usin

g/equ

ipm

ent

Wid

e spe

ctrum

of

Thor

ough

clea

n Ho

t or c

old

Non-

corr

osive

L

ow to

xic

ity

Dise

ases

of

Foot

and

mou

th

Chlor

ine-b

ased

an

imal

path

ogen

s fir

st if

possi

ble.

No ta

int

Anim

als A

ct di

seas

e tes

t iod

opho

rs,

QACs

, Ac

tive i

n pr

esen

ce

BS 5

305

BS 6

734

amph

oter

ics; n

ot of

milk

BS

522

6 ph

enoli

cs

Calf

pens

W

ide s

pectr

um o

f Cl

ean

first.

Ho

t or c

old

Non-

corr

osive

Lo

w to

xicit

y in

Di

seas

es o

f Fo

ot a

nd m

outh

Ph

enoli

cs, i

odop

hors

, an

imal

path

ogen

s Ac

tive i

n pr

esen

ce

use d

ilutio

n An

imal

s Act

dise

ase t

est

gluta

rald

ehyd

e/ of

straw

, exc

reta

-

BS 6

734

pero

xyge

n pr

oduc

ts

Teat

skin

, udd

ers

Activ

e ag

ainst

Activ

e in

prese

nce

Cold

- M

ust n

ot ca

use

Med

icine

s Act

Lyop

hilis

ed p

ig Ch

lorhe

xidin

e, or

gani

sms c

ausin

g of

milk

irr

itatio

n sk

in tes

t iod

opho

r ma

stitis

Fish

farm

ing

Equi

pmen

t/hou

sing

Activ

e aga

inst

fish

Activ

e in

pres

ence

Co

ld No

n-co

rros

ive

Low

toxic

ity

MAF

F Co

de

BS 6

734

Lim

e, ch

lorin

e-pa

thog

ens

of sli

me, f

ish

to fis

h of

Prac

tice

relea

sing p

rodu

cts,

(bac

teria,

fung

i sc

ales o

r pro

tein

hypo

chlo

rite,

and

virus

es)

iodop

hors

, QA

Cs,

sodiu

m hy

drox

ide

Eggs

Ac

tive a

gain

st fis

h Ac

tive i

n pr

esen

ce

Cold

Non-

corr

osive

No

n-to

xic

MAF

F Co

de o

f -

Iodo

phor

s pa

thog

ens

of fi

sh, e

ggs a

nd

to fis

h eg

gs

Prac

tice

(bac

teria,

fung

i re

lated

soili

ng

and

virus

es)

Shee

p fa

rmin

g Ho

usin

g/lam

bing

Sh

eep

path

ogen

s Ac

tive i

n pr

esen

ce

Cold

- Lo

w to

xicity

in

Dise

ases

of

BS 6

734

Phen

olics

, iod

opho

rs,

pens

of

straw

, exc

reta

use d

ilutio

n An

imal

s Act

gluta

rald

ehyd

e/ pe

roxy

gen

prod

ucts

73

Equi

ne p

racti

ce

Activ

e aga

inst

Activ

e in

pres

ence

Co

ld

- Lo

w to

xicity

to

Dise

ases

of

BS 6

734

Phen

olics

, iod

opho

rs,

Equi

pmen

t/hou

sing

equi

ne p

atho

gens

, of

dirt,

hair

, stra

w,

hors

es in

use

An

imal

s Act

BS 2

462

gluta

rald

ehyd

e/ ba

cteria

, fun

gi,

excr

eta.

dilu

tion

BS 5

41

pero

xyge

n vir

uses

Cl

ean

first

if BS

808

co

mbi

natio

ns

possi

ble

CA T

est

Pig f

arm

ing

Equi

pmen

t/hou

sing

Activ

e aga

inst

pig

Activ

e in

pres

ence

Co

ld

- Lo

w to

xicity

to

Dise

ase

of

Swin

e ves

icular

Gl

utar

alde

hyde

, pa

thog

ens

of d

irt, s

traw,

pig

s in

use

Anim

als A

ct

dise

ase t

est

iodop

hors

, ex

creta

. di

lutio

n BS

673

4 ph

enol

ics

Clea

n fir

st if

BS 2

462

possi

ble

BS 5

41 BS

808

CA

test

Poul

try fa

rmin

g Eq

uipm

ent/h

ousin

g Ac

tive a

gain

st Ac

tive i

n pr

esen

ce

Cold

- Lo

w to

xicity

to

Dise

ases

of

Newc

astle

dise

ase

Phen

olics

, iod

opho

rs,

poul

try p

atho

gens

of

litte

r, ex

creta

. po

ultr

y in

use

Anim

als A

ct (fo

wl p

est)

test

glut

aral

dehy

de,

Clea

n fir

st if

dilu

tion.

BS

673

4 fo

rmald

ehyd

e po

ssibl

e N

o ta

int

BS 2

462

BS 8

08

Eggs

Ac

tive a

gain

st Us

ed o

n cle

an

Cont

rolle

d -

Non-

toxi

c and

-

BS 6

424

Form

aldeh

yde,

poul

try an

d eg

gs

cond

ition

s no

n-sta

inin

g BS

647

1 iod

opho

rs, c

hlor

ine-

hum

an p

atho

gens

re

leasin

g pr

oduc

ts, QAC

s

Veter

inar

y pr

actic

e W

ide sp

ectru

m Cl

ean

first.

Som

e Ho

t or c

old

Non-

corr

osive

Lo

w to

xicit

y Di

seas

es o

f BS

673

4 req

uired

so

iling

pre

sent

but

to

surfa

ces

Anim

als A

ct; B

S 24

62

gene

rally

ligh

t an

d in

strum

ents

Med

icine

s Act

BS 5

41

BS 8

08

CA te

st

Abba

toirs

Ho

usin

g/equ

ipm

ent

Wid

e spe

ctrum

Ac

tive i

n pr

esen

ce

Hot

or c

old

- No

n-ta

intin

g M

AFF

Code

of

- Ca

ustic

prod

ucts,

re

quire

d of

blo

od, e

xcre

ta,

Prac

tice

chlor

ine-r

eleas

ing

body

flui

ds, f

at,

prod

ucts

prot

ein. C

lean

first

Laye

rage

W

ide s

pectr

um

Activ

e in

pres

ence

Co

ld

- -

Dise

ases

of

BS 6

734

Iodo

phor

s, of

straw

, exc

reta

An

imals

Act

BS

246

2 ph

enol

ics,

BS 5

41

glut

aral

dehy

de

BS 8

08

BS: B

ritis

h St

anda

rd

QA

C: q

uate

rnar

y am

mon

ium

com

poun

d M

AFF

: M

inis

try o

f Agr

icul

ture

, Fis

herie

s an

d Fo

od

CA: C

row

n ag

ents

74

REFERENCES

1. ANON. (1990). - Guide to the choice of disinfectants. British Association for Chemical Specialities, Lancaster, United Kingdom, 22 pp.

2. BLOCK S.S. (ed.) (1991). - Disinfection, sterilization, and preservation, 4th Ed. Lea & Febiger, Philadelphia & London, 1,162 pp.

3. DOMAGK G. (1935). - Eine neue Klasse von Disinfectionsmitteln. Dt. med. Wschr., 61, 829-932.

4. HASKONING (1994). - Possibilities for future environmental policy on biocides in the European Community. Interim report, June. Haskoning Royal Dutch Consulting Engineers and Architects, Nijmegen, 118 pp.

5. ISHIKAWA M . & MYOSHI Y. (1980). - Bactericidal effect of several disinfectants against Mycobacteria tuberculosis and Mycobacteria bovis. Bokin Bahai, 8 (4), 145-147.

6. JACOBS W.A., HEIDELBERGER M . & AMOS H.L. (1916). - The bactericidal properties of the quaternary salts of hexamethylene tetramine. J. expl Med., 23,569-599.

7. KLARMANN E.G. & W R I G H T E.S. (1950). - Are quaternary ammonium compounds sporicidal? Am. J. Pharm., 122, 330-336.

8. REBOUL A. (1994). - Active substances database. Association Internationale de la Savonnerie et de la Détergence/Fédération Internationale des Associations de Fabricants de Produits d'Entretien, Brussels, 10 pp.

9. SPAULDING E.H. (1967). - Recommendations for chemical disinfection of medical and surgical materials. Public Health Service Publication 930 C-15. Department of Health, Education and Welfare, Washington, D.C., Vol. 1,65-67.