Choice of disinfecting agents

Types of disinfecting agents that might be used during an outbreak of disease in aquatic animals include the following:
  • oxidising agents;

  • pH modifiers (alkalis and acids);

  • aldehydes;

  • biguanides;

  • quaternary ammonium compounds (QACs);

  • ultraviolet (UV) irradiation;

  • heat;

  • drying; and

  • high temperatures.

It is beyond the scope of this manual to discuss all possible types and combinations of disinfectants. Those most likely to be used during an emergency disease event are discussed below. Table 4.5 provides information on the corrosive qualities of common disinfecting agents. Tables 4.6 and 4.7 indicate the relative efficacy of common disinfecting agents against different types of microoganisms, and Tables 4.8 and 4.9 summarise the working characteristics of common chemical agents.

Further details on the practical applications of each type of agent are contained in Part B of this manual. More than one effective disinfecting agent may be used during the decontamination program. For example, more expensive products are often used for critical tasks or the disinfection of personnel, but it may be more appropriate to disinfect large volumes of water using cheaper compounds that are also available in sufficient quantities or consider physical
options such as UV or heat.

The shortcomings of chemical disinfectants can often be improved by adjusting working concentrations and modifying physical parameters of the water used. For example, the antimicrobial effect of iodophors, carboxylic acids and chlorine may be improved by lowering the pH of the solution. With the exception of iodophors and alcohols, increasing concentration generally improves antimicrobial efficacy. Similarly, increased temperature (within a defined range) and contact time also increase the effectiveness of disinfecting agents.

4.2.1 Oxidising agents

The majority of oxidising agents are relatively fast acting and very effective disinfectants for a large range of microorganisms when they are used under appropriate conditions, at a suitable concentration and with acceptable contact times.

Most oxidising agents — apart from iodophor compounds — are corrosive to soft metals such as aluminium, brass and copper, and can damage rubber items such as gumboots and vehicle tyres. Oxidising agents can be neutralised using a reducing agent such as sodium thiosulfate (see Section 7.1 for further details).
Chlorine-liberating compounds
Chlorine-liberating compounds are the most widely used chemicals for disinfection purposes. As indicated in Table 4.4, chlorine compounds considered most suitable for use during decontamination programs fall into three basic categories: hypochlorite compounds, organic chloramines and chlorine dioxide liberators.

Table 4.4

Common types of chlorine-liberating compounds
Chemical group
Common examples
Physical state (concentrate)
Available chlorine (concentrate)
Hypochlorite compounds Sodium hypochlorite
Potassium hypochlorite
Calcium hypochlorite
Lithium hypochlorite
Chlorinated trisodium phosphate
Liquid
Liquid
Powder
Powder
Powder
1–15%
12–14%
65–70%
30–35%
3.25% + detergent action
Organic chloramines Chloramine-T Powder 24–26%
Chlorine dioxide liberators Sodium chlorite + acid Liquid 17%
Source: Adapted from Dychdala (2001)

Hypochlorite solutions release chlorine in the form of hypochlorite ions and hypochlorous acid, which are the active disinfecting agents. Hypochlorite ions have much weaker biocidal action than hypochlorous acid.

Hypochlorous acid and hypochlorite ions occur in equilibrium in solution, with the relative concentration of each determined by either temperature or pH. The concentration of hypochlorite ions increases with either increasing pH or increasing temperature. It is therefore optimal to maintain water pH at or below 7 (a pH range of 6–8.5 for working solutions is recommended) in order to maximise the effectiveness of these disinfecting solutions. In hot environments (>25°C), the increase in hypochlorite ions may need to be compensated for by use of higher hypochlorite concentrations. Section 7.1 contains further details on the properties and uses of hypochlorite solutions.

Chloramine-T is the most commonly used organic chloramine. It is used as a veterinary disinfectant and therapeutic in both terrestrial and aquatic livestock.

The chemistry of chloramine-T is the subject of some debate, but it is generally accepted that, like the hypochlorites, chloramine-T decomposes in water into hypochlorite ions and hypochlorous acid. The organic anion in chloramine-T degrades at a much slower rate than hypochlorites, and this slow degradation makes solutions more stable, less corrosive and less irritant. Chloramine-T is also less affected by the presence of organic matter. Section 7.2
contains further details on the properties and uses of chloramine-T.

Chlorine dioxide has been used to treat drinking water for many years. It is normally a highly reactive gas at room temperature, requiring complex infrastructure for its generation. However, products have recently been introduced onto the market that allow chlorine dioxide to be used for a range of small-scale disinfection applications. These products commonly use sodium chlorite (also referred to as ‘stabilised chlorine dioxide’) solutions that are treated with an acid ‘activator solution’ to generate chlorine dioxide in solution.

Chlorine dioxide does not ionise to form hypochlorite or hypochlorous acid and thus is not subject to the constraints of temperature or pH described above. Chlorine dioxide has a number of significant advantages over other chlorine-based solutions. It is less affected by the presence of organic matter and more tolerant of changes in pH. Chlorine dioxide is also reported by some authors to have greater antimicrobial activity than sodium hypochlorite, particularly against spores (Dychdala 2001). Section 7.3 contains further details on the properties and uses of chlorine dioxide.
Peroxygen agents

Peroxygens include compounds such as hydrogen peroxide, peracid solutions and monosulfates of either sodium or potassium. Peroxygen disinfecting agents are very active, and are not affected by organic matter, but some products may be corrosive to alloys, aluminium and plain steel.

Peracid solutions are a mixture of peracetic acid, hydrogen peroxide and acetic acid. The two latter compounds have a synergistic effect with peracetic acid. They are extremely effective biocides and have no toxic residuals (Block 2001), but their acidic pH makes them corrosive to some materials when used at high concentrations. Peracids are active against all types of microorganisms, including spores, and retain activity in the presence of organic matter (Jeffrey 1995). Although biocidal activity is effective over a wide pH range, peracids tend to be more effective as weak acid solutions.

Powdered forms of peroxygens occur as sodium or potassium monosulfates (eg potassium peroxomonosulfate triple salt). Throughout this document, they will be referred to as monosulfates to differentiate them from other peroxygen agents. Monosulfates produce chlorine when dissolved into solution, and peroxide under acid conditions. They therefore have two actions depending on water pH. One common member of this group has achieved wide acceptance as a general disinfectant in the veterinary industry and is commonly used during emergency livestock disease events.

Section 7.6 contains further details on the properties and uses of peroxygen compounds.

Iodophors

Iodine is a potent disinfecting agent that is effective against a wide range of bacteria, fungi and viruses. The older inorganic aqueous and alcohol solutions of iodine disinfectants are generally toxic and corrosive, making them unsuitable for decontamination programs. These problems have largely been overcome in the group referred to as the iodophors, which are effective and widely used disinfectants.

Iodophors are a complex of iodine and an organic carrier molecule. This increases solubility and allows a sustained release of iodine over time in aqueous solution. These solutions have lower toxicity or irritant effects and are less affected by organic matter (3×) than chlorine disinfection compounds (Gottardi 2001).

A commonly available iodophor is povidone-iodine, which uses a particular type of carrier molecule. Povidone-iodine is particularly nontoxic and noncorrosive. It is commonly used as a general disinfectant in veterinary medicine and is suitable as a disinfectant for skin or delicate equipment. It has gained wide acceptance in aquaculture for disinfection of fish eggs and the control of viruses such as infectious pancreatic necrosis virus.

Other iodophor solutions commonly used for disinfection on farms are acidified solutions, as this enhances their biocidal activity and penetrating ability. These solutions are commonly used in dairies to disinfect milking equipment and remove milk deposits. Such preparations would also have applications in cleaning and disinfection of aquaculture recirculation systems. Due to their low pH, acidified iodophor solutions may be corrosive to some materials. Iodophors have the unique characteristic of producing higher levels of free molecular iodine (the disinfecting agent) when diluted. The concentration of free molecular iodine rises 10-fold with a 1:100 dilution of 10% povidone-iodine solution; further dilution reduces the biocidal effect (Gottardi 2001). The optimum working solution, for maximum free molecular iodine, is therefore 0.1% povidone-iodine.

Because free iodine gives iodophor solutions their brown colour and solutions lose colour as iodine is consumed, colour may be used as an indicator of exhaustion of the iodine in the solution.

Section 7.4 contains further details on the properties and uses of iodophors.

4.2.2 pH modifiers

Alkalis

Alkalis, which act by raising the ambient pH to very high levels, are effective against a wide range of pathogens. Compounds such as sodium hydroxide and sodium carbonate are commonly included in the formulation of cleaning compounds. When used at high concentrations, they also have significant antimicrobial properties. Strong alkalis, at pH 12 or more, have excellent activity against all categories of viruses but are very slow acting compared with oxidising agents.

Alkalis retain their effectiveness in the presence of heavy burdens of organic matter, assist the penetration of soiling through their saponifying action on fats, and are effective in loosening organic matter. They are particularly useful for decontaminating ponds, drains, effluent waste pits and carcase disposal pits. Unlike acids, they may also be used on concrete surfaces.

Alkalis are corrosive to some metal alloys, and care should be taken when treating metal or painted surfaces. They are also irritant to skin and mucous membranes, and staff must be supplied with appropriate safety equipment.

Section 7.5 contains further details on the properties and uses of alkalis.

Acids

The antimicrobial activity of acids depends on the concentration of hydrogen ions, which destroy cell amino-acids and precipitate proteins (Maris 1995, Quinn and Markey 2001). Acids act slowly and, although they have specific benefits as disinfectants, their use on their own is limited. They are more likely to be used as adjuncts to other compatible disinfecting agents, such as iodophors, where they produce optimal pH and enhance penetration or rinsing qualities. They are commonly used in heated water for disinfection of pipework in dairies, a process that may also have some application in the disinfection of hatchery pipework.

Many organic acids (eg formic and citric acid) are used in disinfection formulations to enhance fungicidal and virucidal properties. They may also be mixed with anionic detergents to enhance sanitising capabilities.

As with alkalis, all acid solutions (with the exception of peracid solutions) are slow acting.

4.2.3 Aldehydes

Aldehydes act by denaturing protein. Two aldehyde compounds that may be used during decontamination of aquaculture facilities are formaldehyde and glutaraldehyde. They are highly effective against a wide range of organisms, but are also relatively slow in action. Aldehydes maintain their activity in the presence of organic matter and are only mildly corrosive. Their main disadvantages are the irritating fumes produced, their expense and their carcinogenic properties.

Formalin is a 40% aqueous solution of formaldehyde gas. Formalin diluted to 8% (dilution factor of 12) is considered effective against most viral groups (AUSVETPLAN Decontamination Manual
15). Glutaraldehyde is approximately three times more active than formalin and is commonly used at a concentration of 1–2%.

Formaldehyde gas is sometimes used to fumigate equipment and premises. For gaseous formaldehyde to be effective, the gas concentration, gas distributions, temperature, humidity and contact time must be carefully controlled. In order to be effective, it requires high relative humidity, temperatures above 13°C and contact times of at least 12 hours. Formaldehyde gas is extremely toxic and, given the conditions required for it to be an effective disinfectant, its use is limited to specific situations. It might be considered, if appropriate under the jurisdiction’s legislation, for sealed spaces that are otherwise difficult to disinfect (such as cool rooms, boat holds and complex pipework), or in tropical hatcheries where ambient conditions (temperature and humidity) are suitable.

Section 7.7 contains further details on the properties and uses of aldehydes.

4.2.4 Biguanides

Of the many biguanides available, chlorhexidine is probably one of the most commonly used. Chlorhexidine preparations do not irritate tissues and are commonly used as skin disinfectants. However, they are not effective in hard or alkaline water and are less active against most types of pathogens than many other disinfectants. The use of chlorhexidine during emergency disease events would generally be restricted to use as a skin cleansing agent or disinfectant for delicate materials.

4.2.5 Quaternary ammonium compounds

The biocidal efficacy of QACs is variable and selective. They are effective against some vegetative bacteria and some fungi, but not all viruses (Treeves-Brown 2000, Ritcher and Cords 2001). QACs are most active against gram-positive bacteria; action against gramnegative bacteria is slow, with some strains showing resistance. These compounds are not effective against spores.

The advantages of QACs are that they are odourless, noncorrosive and nonirritant, and have wetting properties and low toxicity to mammals. They also retain activity over a wide pH range (pH 3–10.5), are stable at higher temperatures, are not generally affected by organic matter and maintain a residual effect on treated surfaces. Hard water and anionic detergents inhibit QACs, limiting their use to freshwater situations.

As with chlorhexidine, QACs are more commonly used for sanitation than disinfection. Since they are also cleaning agents, they may be used to combine the cleaning and disinfection stages, where appropriate.



4.2.6 Ultraviolet irradiation

UV irradiation is a viable option for the treatment of water entering and/or leaving aquaculture facilities where there is some control over water flows (eg semi-closed systems such as hatcheries or shore-based abalone farms, and closed systems such as recirculation facilities) and where other chemical or  heat treatments are not viable options.

UV disinfection systems use low-pressure mercury lamps enclosed in quartz tubes, which allow passage of UV radiation at a wavelength of approximately 260 nm (Bitton 1994). The tubes are immersed in flowing water channels.

Some units also use a titanium dioxide catalyst that, when irradiated with UV light, produces superoxide ions and hydroxy radicals that increase the disinfection capability. These systems are lightweight and function over a range of temperatures, pressures and pH (McDonnell and Pretzer 2001). Similar units have recently been used to control fungal infections in finfish hatcheries.

The efficacy of UV disinfection depends on the type of microorganism, the clarity of the water, the intensity of light and the exposure time. Variables such as suspended solids, water flow rates and water clarity affect the efficacy of UV irradiation and thus the practical disinfecting capability.

In general, resistance to UV follows a similar pattern to that described in Table 2.1 (Bitton 1994). The major disadvantage of UV irradiation in emergency disease events is its ineffectiveness against a number of fish pathogens, particularly viruses. Although Torgersen (1998) demonstrated that infectious salmon anaemia (ISA) virus was inactivated by moderate levels of UV, the infectious pancreatic necrosis (IPN) virus is considered to be UV resistant. Very high doses are also required for shrimp baculoviruses (Chang et al 1998). Vegetative bacteria and enveloped viruses may require only 10 mJ/cm2 of UV irradiation, but non-enveloped viruses (category B and C) may need as much as 200 mJ/cm2 (Bitton 1994). UV disinfection is not a suitable primary method of treatment for waters during emergency disease events involving category B viruses.

For UV to be effective, water must be pretreated to remove contaminants that could inhibit light penetration. Flocculation and filtration of waste water before irradiation significantly improve the disinfecting effect and reliability of UV radiation units. Water filtration and UV units must also be matched to maximum water flow rates to ensure that the output is capable of treating peak water flows. Filtration to 50 μm before UV irradiation is recommended for most situations.

Although it is unlikely that UV radiation would be used during initial stages of an emergency response, commercial units are now available in a range of sizes that can be added to existing production and processing facilities. These should be considered if environmental contamination by chemical disinfectants is a significant concern, or it is anticipated that a disinfection process for water leaving infected premises will be required for some time. UV irradiation may also be used to treat inlet water to safeguard facilities from reinfection.

4.2.7 Ozone

As with UV irradiation, ozone treatment would not normally be available during the early phase of an aquatic animal disease emergency event. However, ozone is highly efficient at disinfecting water and, where available, has an important role in the ongoing treatment of water entering or leaving facilities.

Ozone is normally generated on site by passing dry air and oxygen between electrodes separated by a glass or ceramic plate. The ozone is then injected into water in a specialised ozone contact vessel designed to provide adequate control over residual ozone concentration and water contact time.

As with other oxidative disinfectants, organic matter consumes ozone, and the initial ozone concentration tends to drop rapidly in treated water, making reliable dosing levels difficult to predict. In practice, it is important that the initial ozone dose is high enough to account for oxidation demands, thereby establishing sufficient residual concentration for the required contact time. Ozone dose trials in river water indicated that an initial dosing level up to 4 mg/L was required to maintain a residual level of 0.2 mg/L for 10 minutes (Summerfelt and Hochheimer 1997).

Although the relative susceptibility of pathogens to ozone is similar to that described for UV radiation, ozone has been shown to be effective against a wide range of fish viruses, including category B viruses. Residual levels of 0.2 mg/L have been shown to inactivate IPN virus (a category B virus) after 1 minute (Wedmeyer et al 1979).

Residual ozone levels of at least 0.5 mg/L applied for a minimum of 10 minutes or 1 mg/L for at least 1 minute are recommended during emergency disease events.

4.2.8 Heat

Where circumstances permit, heat may be used as a disinfecting agent. The effect of heat is completely dependent on time and temperature, and these will vary depending on the type of organism being treated. Unless heat is used under controlled conditions, such as autoclaves, it is difficult to maintain these variables for practical disinfection purposes. However, if combined with other forms of treatment, heat processes are excellent supplementary methods for decontaminating equipment such as transport bins, tanks or machinery.

Under most conditions, moist heat is more effective than dry heat as a disinfecting agent. The use of steam or hot water pressure cleaners to apply wet heat to surfaces is likely to be the most common form of heat process during an emergency disease response. These types of steam/heat pressure cleaners are readily available (see Section 3.4.5). Although their primary purpose is to loosen buildups of soil, the heat applied can also have some disinfecting properties; however, it is important to note that there may be significant loss of temperature between the unit and the treatment area. It has been demonstrated that a steam jet of 1300°C applied 15 cm from the surface results in no more than 800°C. This effect is further exacerbated where the treatment surface is metal, thus allowing heat to be conducted away. In this case, depending on how long the jet is applied, temperatures may
reach no more than 350°C (Salvat and Colin 1995).

Heat is also an important tool for disinfecting small volumes of contaminated water. This process is used in some laboratories to treat aquarium waste water before its release.

The use of ‘flame guns’ has been promoted in some literature as an effective method for applying dry heat to large areas, such as buildings, concrete tanks or other nonflammable structures. However, flame guns are difficult to source and are associated with major workplace safety risks. Although they would be suitable for treating large concrete ponds, in practice their use is unlikely and not recommended.

4.2.9 Desiccation

For many pathogens, desiccation is an effective disinfecting process and should not be underestimated as a final stage to the decontamination process. Practical applications for dry heat include the use of heat rooms for diving equipment to ensure that suits and other delicate equipment are thoroughly dried at the end of each day.

In Australia, the hot, dry climate is an important disinfecting tool that is often overlooked. Leaving equipment to dry in areas exposed to sunlight is an extremely effective adjunct to other disinfection processes.

4.2.10 Biological disinfection

Processes involved in the biological breakdown of organic matter should not be overlooked as viable options for inactivating pathogens. Biological processes result in enzymatic degradation, as well as changes in oxygen content, moisture content, pH and temperature. All of these processes can act to inactivate pathogens in infected material.

Potential biological disinfection processes include deep burial, composting, soil injection and reticulation. The first three methods are viable options for the safe disposal of solid biological material and should be considered for carcases, faecal matter and other organic solids.

Whereas deep burial relies on anaerobic decomposition, composting utilises aerobic decomposition to generate heat (up to 70°C) and convert soft tissue and bone to humus over a 40–60-day period (Kube 2002). With the exception of category B viruses and spore-forming pathogens, the majority of fish pathogens can be inactivated by the temperature profile of well-managed compost heaps.

Soil injection, or the maceration and incorporation of wastes into surface soils through cultivation, may be used for both solid and liquid wastes. It relies on bacterial degradation of soil bacteria.

Reticulation may only be used for contaminated water. It uses bacterial degradation, desiccation and UV irradiation as the mechanisms for disinfection.

Soil run-off and drainage should be taken into consideration when choosing disposal sites for the methods described above.

Table 4.5                                                     

Corrosive qualities of some commonly used chemical disinfectants
Disinfectant
Common examples
Corrosive against
Relative corrosive strength
Oxidising agents Chlorine Metal alloys
Rubber compounds
Moderate/high
Chlorine dioxide Metal alloys Moderate/high
Iodophors a, b Metal alloys Low/moderate
Strong alkalis Sodium hydroxide c Metal alloys
Aluminium
High
Calcium hydroxide Metal alloys
Aluminium
High
Acids Acidified iodophors Concrete
Metal alloys
Moderate
Peracids d Concrete
Rubber
Metal alloys
Low
Organic acids Concrete Low
a    Corrosive only at higher temperatures (>40°C)
b    Dependent on pH of specific formulations
c     Highly corrosive to aluminium
d    Corrosive to steel and copper
Source: Compiled from Bruins and Dyer (1995), Quinn and Markey (2001) and Ritcher and Cords (2001)

Table 4.6

Relative susceptibility of viruses, fungi and protozoa to disinfecting agents
Disinfecting agent
Virus category A
Virus category B
Virus category C
Fungi
Spore-forming protozoa
Strong alkalis
+ +
+
+ +
+ +
+
Aldehydes
+ +
+
+ +
+ +
+
Peracetic acid
+ +
+ +
+ +
+ +
+
Chlorine
+ +
+
+ +
+ +
+/– a
Chlorine dioxide
+ +
+ +
+ +
+ +
+
Iodophors
+ +
+/–
+ +
+ +
+/– a
Ozone
+ +
+
+ +
+
+/–
Ultraviolet
+
+/–
+
+
?
QACs
+/–
+
Acids
+
+/–
Biguanides
+
QAC = quaternary ammonium compound
a   High concentrations required to be effective
Key:
++:   Highly effective
+:     Effective
+/–:  Limited activity
–:     Not recommended
?:     Limited information

Table 4.7

Relative susceptibility of bacteria to disinfecting agents
Disinfecting agent
Gram-negative
Gram-positive
Mycobacteri a
Rickettsia-like
Bacterial spores
Strong alkalis a
+ +
+ +
+
+ +
+
Aldehydes b
+ +
+ +
+
+
+
Peracetic acid
+ +
+ +
+ +
+ +
+
Chlorine
+ +
+ +
+ +
+ +
+
Chlorine dioxide
+ +
+ +
+ +
+ +
+
Iodophors b
+ +
+ +
+ +
+ +
+
Ozone
+ +
+ +
+ +
+ +
+
Ultraviolet
+ +
+ +
+
+ +
?
QACs
+/–
+
+
Acids b
+
+
+/–
+
+/–
Biguanides
+
+
+
QAC = quaternary ammonium compound
a High concentrations required to be effective
b Prolonged contact times required in some circumstances; in particular, for spores
Key:
++:   Highly effective
+:     Effective
+/–:  Limited activity
–:     not recommended
?:     Limited information

Table 4.8

Working characteristics of main chemical disinfectant groups
Disinfecting agent
Effective pH working range
Relative chemical hazard to user (concentrate)
Relative chemical hazard to user (working solution)
Relative chemical hazard to environment
Comparative corrosion characteristics
Stability of working solution
Alkaline compounds
Alkaline conditions
10.0
7.0
8.0
10.0
>7 days
Acids
Narrow pH 2–3
 
8.0
5.0
2.0
3.0
>7 days
Hypochlorite compounds
Moderate
8.0
4.0
3.0
8.0
1 day
Chloramine-T
Moderate
8.0
3.0
3.0
6.0
2 days
Iodine (iodophors)
Moderate pH 2–6
 
6.0
2.5
6.0
6.0
5 days
Peracid solutions
Wide
7.0
0.5
0.5
4.0
1 day
Monosulfates
Wide 
6.0
2.5
3.0
8.0
5 days
Chlorine dioxide solutions
Wide
8.0
7.0
1.0
8.0
<1 day
Aldehydes
Wide
10.0
8.0
6.0
1.0
>7 days a
Quaternary ammonium compound
Wide pH 3–10.5
1.0
0.5
4.0
0.5
>7 days
a   In sealed containers
Source: Adapted from summary information provided in Bruins and Dyer (1995) and Ritcher and Cords (2001)

Key:

Italic = Poor working characteristics

Bold = Acceptable working characteristics

Normal = Good working characteristics

Table 4.9

                                                                                                                             
Major advantages and disadvantages of main chemical disinfectant groups
Chemical disinfectant group
Inactivation by organic matter
Wetting ability
Temperature tolerance
Effect of hard water
Effectiveness against mineral deposits
Residual activity
Foaming characteristics
Inhibitors
Acids
Stable
Good
Wide; some loss at very low temperatures
Low
Effective
Slight residual bacteriostatic activity
Low
Cationic surfactants Very low temperatures
Chlorine compounds
Loses activity rapidly
None
Wide
None unless alkaline
None
Limited
Nil
Organic matter High pH
Iodophores
Moderate to high loss of activity
Moderate to good, depending on formulation
5–40°C
Loses activity below 50°C, and gives off gases above 120°C
Moderate
Limited, dependent on pH of formulation
Some
Moderate, dependent on formulation
Hard water
Organic matter Temperature extremes High pH
Peracid solutions
Low to moderate loss of activity
Dependent on product formulation
Wide
None
Limited effect due to acid nature
Some
Low, unless combined with a surfactant
Copper, iron, manganese and chloride ions
Chlorine dioxide
Low to moderate loss of activity
None
Wide
None
None
Some
Nil

Aldehydes
Stable
None
Moderate; gives off fumes at higher temperatures
None
None
Some
Nil

Quaternary ammonium compounds
Moderate to Stable
Good
Stable
Inactivated by hard water
None
Some
High
Very low temperatures
Anionic detergentsor wetting agents

Key:

Italic = Poor working characteristics

Bold = Acceptable working characteristics

Normal = Good working characteristics

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