Disinfectants are chemical agents designed to inactivate or destroy microorganisms on non-critical, semi-critical inert surfaces such as hospitals, buildings, walls, water pools, doors, household appliances, agricultural tools, medical devices and equipments. Different disinfectants have distinct characteristics and effective against microorganisms depending on their chemical nature, concentration and contact time. Consequently, these chemical disinfectants possess many advantages and disadvantages over others. The characteristics of few commonly used chemical disinfectants are discussed in this article.

Alcohol based disinfectants:

Generally, Ethyl alcohol (Ethanol) and Isopropyl alcohol (Propanol) are two common alcohols used as active agents in surface disinfectants. They are always used after dilution with water, since absolute alcohols are less effective on microorganisms. The microbicidal activity of alcohols is achieved at the concentration range of 60-90%. The effectiveness of alcohol also increases as the molecular weight increases. That’s why isopropyl alcohol (IPA) is more efficient disinfectant than ethanol. The pros & cons of alcohol based surface disinfectants are illustrated briefly:

Advantages:

Alcohols are effective bactericides, fungicides, tuberculocidal and virucidal agents.

They rapidly kill most of the microbes within seconds. However, the efficient action time depends on the type of organisms and the concentration range of alcohols used in the disinfectant solution. For instance, the gram-positive organisms Staphylococcus aureus and Streptococcus pyogenes can be killed in 10 seconds by ethyl alcohol concentrations of 60%–95%.

Alcohols inherit pleasant and characteristic odour and even remain stable if stored properly.

They are generally non-toxic, non- irritant, non-allergic in nature.

Alcohols are inexpensive, easily accessible and useable materials.

They evaporate quickly without leaving any residues on the treated surface. That’s why no further need to rinse the surface.

Disadvantages:

Alcohols are not effective against bacteria spores and hydrophilic viruses.

They are volatile and inflammable.

They are less compatible with plastic and rubber surfaces.

Quaternary Ammonium Compounds

QACs are broadly known disinfectant used for sanitization in hospitals and noncritical surfaces such as floors, furniture, and walls, agricultural tools and vehicles and clinical settings (medical equipments).

Advantages:

Quaternary Ammonium Compounds are effective against gram positive and gram negative bacteria, fungi, lipophilc (enveloped) viruses.

They also possess detergent and surfactant properties.

QACs exhibits pleasant aromatic smell.

They are generally non-toxic and non-allergic in nature.

QACs are inexpensive, easy to prepare and use.

QACs are EPA registered as disinfectants.

Disadvantages:

QACs are less effective against gram negative bacteria, tuberculosis bacteria, bacterial spores and hydrophilic viruses.

The quaternaries are good cleaning agents but become less effective biocides with high water hardness and materials such as cotton and gauze pads because these materials absorb the active ingredients.

Development of gram-negative bacteria has been found in the preparations of these QAC based disinfectants.

Prolonged exposure to QAC can cause skin irritation and even cause dermatitis.

Quaternary ammonium based disinfectants can be neutralized by soaps.

Phenolics compounds: Phenol has occupied a prominent place in the field of hospital disinfection for past few decades. Ortho-phenylphenol and ortho-benzyl-para-chlorophenol are two commonly found phenol derivatives in hospital disinfectants.

Advantages:

Effective on wide spectrum of microbes, including bacteria (especially gram positive bacteria), enveloped viruses and fungi.

They are stable during storage.

Phenols are readily miscible with additives such as soaps or detergents and acts as good cleaning agents.

Many phenolic germicides are EPA registered as disinfectants for sanitization of environmental surfaces (e.g., bedside tables, bedrails, and laboratory surfaces) and noncritical medical devices.

Disadvantages:

Poorly effective against bacteria spores and hydrophilic or non-enveloped viruses.

Their activity or effectiveness against microbial agents decreases in the presence of organic matter.

Residual disinfectant remains on porous materials may cause tissue irritation even when rinsed thoroughly.

Prolonged exposure may irritate the skin.

They are toxic and corrosive in nature. The use of phenolics in nurseries is questioned because of toxicity to infants. [4]Phenol is no longer used as a disinfectant due to its toxicity and carcinogenicity.

Some phenolic disinfectants possess unpleasant odour.

Peroxides:

Hydrogen peroxide: It is a strong oxidizing disinfectant. Hydrogen peroxide is one of the safest types of disinfectants, both for human health and environment.

Advantages:

Hydrogen peroxide is extremely effective against a wide range of microorganisms, including enveloped and non-enveloped viruses, vegetative bacteria, fungi and bacterial spores.

Hydrogen peroxide breaks down into environmentally-friendly compounds that are water and oxygen.

To use as high-level disinfectant, hydrogen peroxide is also blended with paracetic acid.

Hydrogen peroxide has quick activity time against microbes, even at small concentrations. A 0.5% accelerated hydrogen peroxide can kill bacteria and viruses in 1 minute and mycobacteria and fungi in 5 minutes. It is also demonstrated in a study that a 0.5% hydrogen peroxide antimicrobial is highly efficient at disinfecting medical devices.

They do not irritate the skin at recommended concentrations (3 to 5%). Also, hydrogen peroxide is poorly absorbed by skin.

3% Hydrogen peroxide solution is easily available.

As per the WHO, the concentration of hydrogen peroxide recommended is 0.125% (v/v) can be used in the formulation of handrub or hand sanitizer.

Disadvantages

It is corrosive and reacts with oxidizable materials aluminium, copper, brass, zinc, iron, bronze, manganese, chromium, lead and silver.

Hydrogen peroxide disinfectants can be toxic to human, if inhaled or ingested and may cause gastrointestinal and respiratory issues such as gas embolism, gastric irritation, gastric distension, and upper airway irritation, inflammation of the nose, hoarseness, shortness of breath, and a sensation of burning or tightness in the chest.

At high concentrations (>10%), hydrogen peroxide is corrosive to skin, eyes, and mucous membranes, even lower concentrations may cause irritation.

Peracetic acid: It is used in widely used disinfectant for sanitizing automated machines to chemically sterilize medical, surgical, and dental instruments (e.g., endoscopes, arthroscopes).

Advantages:

Like hydrogen peroxide, peracetic or peroxyacetic acid acts rapidly against all the organisms.

Percetic acid also decomposes in to safer products acetic acid, water, oxygen, hydrogen peroxide.

It does not leave any residue on the treated surface.

Peracetic acid remains effective in the presence of organic matter.

Disadvantages:

Peracetic acid can corrode copper, brass, bronze, plain steel, and galvanized iron.

It is considered unstable, particularly when diluted. For instance, a 1% solution loses half its strength through hydrolysis in 6 days, whereas 40% peracetic acid loses 1 to 2% of its active ingredients per month.

Hypochlorites: Sodium hypochlorites and calcium hypochlorites are broadly known hypochlorite solutions as disinfectants and household bleaches in the concentration range of 5.25 to 6.15%. Sodium Hypochlorite (NaOCl) is the most frequently used hypochlorite based disinfectant, used in the form of spraying or mist solutions. [3]Hypochlorite containing household bleach is typically diluted with water in the mixing ratio of 1:50 (1000ppm) for surface disinfection. These solutions have been recommended for use in both hospitals and the community as disinfecting solutions.

Advantages:

Hypochlorites are very effective to destroy and prevent the growth of all types of microorganisms including spores.

They have rapid microbicidal activity, depending on the concentration and contact time.

Hypochlorites exhibit deodorizing and sanitizing properties.

They are low cost disinfectants.

They are non-staining colourless disinfectants.

Disadvantages:

Both Sodium hypochlorites and calcium hypochlorites are toxic substances due to the presence of harmful hypochlorite moiety. They can be harmful for both human and environment.

Human exposure of hypochlorites vapours and the gases such as chlorine or chloramine liberated from hypochlorite disinfectant solution can be very harmful via any mode of contact i.e., dermal, inhalation and ingestion. It can cause burning of the eyes, nose, and throat; redness, blisters, coughing, diarrhea, vomiting, liquefaction necrosis and damage to lungs.

Hypochlorites are toxic in nature.

Sodium hypochlorite is very toxic to aquatic organisms.

Sodium hypochlorite leaves residues after disinfection.

Hypochlorites are corrosive to metals.

After dilution, shelf life of hypochorite solutions shortens (1:9 parts water)

Hypochlorites inactivate in the presence of organic matter.

This article has been prepared from various on-line references to create a public awareness on major surface disinfectants particularly to deal with COVID 19 pandemic situation