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Key Characteristics Of The Principal Hard Surface Disinfectants
Since Lister showed in 1867 that phenol (carbolic acid) would kill microorganisms, many
chemicals have been tested for this purpose, and a few have proved to be effective.
These chemicals can be classified relative to our principal area of interest, that is,
hard surface disinfection. The following are undoubtedly the most important.
1. Quaternary ammonium compounds
2. Phenolic compounds
3. Iodophors
4. Pine oil
The following discussion will examine the relative advantages of each of these chemicals
within the context of their use when formulated with a detergent material to form a hard
surface detergent/disinfectant. To do this, however, it is necessary first to consider
what we mean by a good disinfectant.
The first criterion obviously is that it kills microorganisms of all kinds, particularly
the pathogens, although destruction of others which are considered harmless to humans and
animals is sometimes also important.
Many non-pathogens attack organic matter, producing chemicals which may be highly odorous,
corrosive or staining. Elimination of such organisms is certainly a plus factor to be
desired from any product. Germicidal products which kill a wide range of microorganisms
are said to be broad spectrum.
It must be emphasized that hard surface disinfection can best be achieved when it is
accomplished as part of a one step operation involving a detergent. If a germicidal agent
is applied to a dirty surface, it will kill those organisms which it contracts, but most
of them will probably be surrounded by soil and be unaffected by the chemical. Thus it is
important that the disinfectant chemical be compatible with the detergent system with
which it is to be combined. of course, one could always do the job in two steps - first
clean the area, then treat it with a disinfectant. This procedure will be highly effective
in terms of reducing or eliminating the bacterial load on the surface but it has two major
drawbacks. Labor cost is approximately 95% of the cost of maintenance, and by requiring
that an area be treated twice - first for detergency, then for disinfection - labor cost
is doubled. This is an extremely important consideration, and it explains the almost
complete disappearance of single service disinfectant products. Most products today
combine detergency with
disinfectants so that the job can be done in one operation.
Actually, the matter of labor cost is rather minor when compared to the other drawback. A
two step operation of cleaning followed by disinfection greatly increases the possibility
and dangers of cross contamination. Consider what happens during the cleaning operation.
The custodian applies a detergent solution on the area to be cleaned, then picks it up
with a mop or wet vacuum, and finally disposes of the solution containing the picked up
soil. The overall effect of this activity has been to concentrate into the dirty water all
the microorganisms that have been picked up in the cleaning process. Unless handled with
great care, this contaminated solution can contribute to the spread of contamination. Not
only is the combination product more cost effective but it will provide far better overall
result.
Most detergent/disinfectant products are produced as liquid concentrates which must be
diluted with water before use. In handling these products, either as the concentrates or
the use dilutions, it is difficult to avoid having them come into contact with the skin.
In an extreme case, an accident may occur in which some of the product may be splashed
into the face, perhaps into the eyes. An important requirement, therefore, for this type
of product is safety -freedom from irritation if product gets on the skin or in the eyes
and freedom from toxicity if it is ingested.
In the evolution of environmental sanitation, (hard surface cleaning) the removal of
unwanted physical soil was followed by sanitizing or disinfection for the destruction and
removal of microorganisms. Eventually, these two functions were combined so that only one
product was needed. However, it was later recognized that there is a third important
dimension to environmental sanitation - odor control. Unpleasant odors are an unfortunate
fact in most hospitals, nursing homes, mental institutions, schools and many other
facilities. counteracting these odors required incorporating an odor control system into
the detergent/disinfectant product.
To this end, it is advantageous to begin with a detergent/disinfectant that has little or
no odor. Chemicals like phenol are highly odorous and they are almost impossible to
effectively mask or neutralize. Consequently, detergent/disinfectant products which
incorporate phenol derivatives have that tell tale "Hospital odor".
Quaternaries, on the other hand, have a very low almost nondescript odor and can thus be
readily combined with odor control ingredients.
An important factor in detergency is pH which is a measure of acidity or alkalinity. A
product with a pH of 7 is neither acid nor alkaline. It is neutral. Below 7, the product
is acid; above 7, it is alkaline. As the pH of a detergent solution rises, i.e., becomes
more alkaline, the cleaning efficiency of the product increases. There are limits to this,
of course, since too high a pH will frequently result in deleterious effects on the
surface being cleaned.
In general, a pH no higher than 10.5 is acceptable. This does not mean that a product is
safe at 10.5 and harmful at 10.6. There is a range in which harmful activity will begin,
and the breadth of this range is dependent on the other ingredients in the formulation. As
a general rule, the use of a pH of 10 gives us a cut-off point with a built-in measure of
safety. Another highly important factor is the use of inorganic builders and chelating
agents to improve detergency. These agents operate best in an acid medium. Thus, it is
apparent that disinfectant chemicals intended for use in a combination product should have
good activity at an alkaline pH up to 10.
One final factor requires consideration. The activity of all disinfectant chemicals is
affected adversely by organic matter. The degree to which this occurs varies with the
particular chemical and probably with the type of organic soil present. Thus. it is
advantageous to choose. as the germicidal component of the product. one which is least
affected by organic matter.
Having examined the major characteristics to be evaluated in electing the proper
germicidal chemical for a
detergent/disinfectant product, we can now evaluate the most important available biocidal
chemicals. A recap of these characteristics gives us the following:
1. Broad spectrum activity
2. Compatibility with effective detergents
3. Low oral toxicity and skin irritation
4. Freedom from odor
5. High activity at same pH as the detergent component
6. Retention of activity in presence of organic matter
QUATERNARY AMMONIUM COMPOUNDS
1. Spectrum of Activity
Hundreds of different quaternaries have been prepared and tested. Some are good clothes
softeners. Others are effective antistatic agents for certain application. A relatively
small number have been found to be highly effective germicidal agents. Of this last group,
an even smaller number are bactericidal and fungicidal against an extremely wide range of
microorganisms. This activity covers both the gram positive and gram negative bacteria,
fungi and viruses. We can say, then, that selection of the proper quaternary will give a
product with a wide spectrum of activity.
2. Detergent Compatibility
The most effective of the products available for use as hard surface detergents are the
synthetic nonionics. Properly formulated, the quats are compatible with these materials.
3. Low Oral Toxicity and Skin Irritation
All disinfectant chemicals have some degree of toxicity and irritation in concentrated
solution. Many of them carry these properties over into the low concentrations required
for effective disinfection. This is not true of the quats. Use concentrations of 400-500
ppm of quaternary are normally used for disinfection. At these concentrations, the product
is not irritating and has an extremely low order of oral toxicity.
4. Freedom From Odor
Quaternary ammonium chlorides are odorless.
5. High Activity at Alkaline pH
The germicidal activity of quats increases as the pH increases. This means that optimum
germicidal and detergent activity can be obtained from a quaternary/nonionic combination,
since both show increasing activity with increasing pH.
6. Retention of Activity of Organic Matter
All disinfectant chemicals are adversely affected to some extent by organic matter. The
effect may be large or small. Quats are among the least affected in the presence of
organic matter.
PHENOLIC COMPOUNDS
1. Broad Spectrum Activity
Individual phenolics are limited in range with regard to the number of different types of
micro-organisms. they will kill. However, the number of available phenolics is large and
an effective formulation can be produced by combining several different phenolics.
2. Detergent Compatibility
Phenolics are not compatible with the noionics, the most effective of the hard surface
detergents. They are compatible with soaps and/or synthetic anionic detergents. The
resulting formulation is, of course, a relatively ineffective detergent product, and as a
result, less effective germicide.
3. Oral Toxicity and Skin irritation
Most phenolics have a relatively high toxicity rating and are usually skin irritants,
especially so in the concentrations in which they are present in the typical formulation.
4. Freedom From Odor
All of the phenolics have a noticeable odor and most of them a disagreeable one.
5. High Activity at Alkaline DH
Phenolics are most effective against microorganisms at a pH 8 or below. This is usually
too low for good detergent action. As the pH increases above 8, germicidal activity
decreases.
6. Retention of Activity in Presence of Organic Matter
The activity of some Phenolic compounds decreases quite rapidly in the presence of organic
matter. The degree will vary with the type of Phenolic, but as a general rule, the
phenolics most effective against microorganisms are moderately affected by organic matter.
IODOPHORS
The type of iodophor always found in the area of detergent/disinfectants is one based on a
combination of iodine and nonionic synthetic detergent in an acid medium. The acid is
usually phosphoric and the product normally has a pH of 3-4.
1. Broad Spectrum Activity
Iodophors are excellent in this respect.
2. Detergent Compatibility
As a stated before, the type of iodophor normally encountered is a combination of iodine
and nonionic. Unfortunately, since germicidal activity of iodine is highest at an acid pH,
the detergent activity of the nonionic is very sharply reduced.
3. Oral Toxicity and Skin Irritation
Iodophors exhibit relatively low toxicity and skin irritation.
4. Freedom From Odor
Iodophors have a very low odor level and in this respect are not objectionable. However,
they cannot be formulated with odor counteractants or other materials which would normally
leave an air freshened effect, since the iodine attacks the odor counteractant chemicals,
usually creating an unpleasant odor in the process.5. High Activity at Alkaline pH
As stated before, these products require an acid pH for germicidal activity. This, of
course, drastically reduces the efficacy of the detergent. It also eliminates the
possibility of using inorganic builders sequestrants and chelating agents to enhance
detergent activity.
6. Retention of Activity in Presence of organic Matter
The presence of organic matter sharply reduces the efficacy of iodophors against
microorganisms.
PINE OIL
This product is obtained by several methods from pine wood. It is a mixture of several
different chemicals which vary in
their activity against microorganisms. The National Formulary specifies that 95% of the
product must distill between 200 and 225 C. This specification tends to fix the types and
amounts of chemicals present in the product. A typical pine oil preparation contains 60%
pine oil solubilized with soap. Because of certain limitations, to be discussed, these
products are frequently fortified by the addition of phenolics. However, it has been found
that the phenolics are slowly inactivated over an extended period of time, so that the
presence of Phenolic in a pine oil product does not necessarily mean it will be active.
The unfortified pine oil formulation must be used in fairly concentrated form, so they are
uneconomical for hard surface cleaning and disinfection where large surfaces are involved.
1. Broad Spectrum Activity
Pine oil is quite active against the gram negative organisms, but totally ineffective
against many of the gram positive organisms, such as Staphylococcus Aureus. The addition
of a Phenolic is necessary to give activity against the gram positives, but, as pointed
out previously, there is a slow inactivation of the Phenolic compound.
2. Detergent Compatibility
Pine oils are compatible with soaps and some anionics. Neither type of detergent is really
effective for hard surface cleaning and both, particularly the soaps, will leave a
metallic plate if hard water is used.
3. Oral Toxicity and Skin Irritation
Pine oil itself has low order of toxicity and skin irritation. Combined with phenolics,
both toxicity and skin irritation are definitely increased.
4. Freedom From Odor
Pine oil itself has a very high odor level which is objectionable to many people. As an
odorant, it is frequently used to mask such malodors as those commonly encountered in
poorly maintained rest rooms.
5. High Activity at Alkaline pH
Activity of these products is good at fairly high pH. When a Phenolic is present, its
activity is, of course, decreased under such conditions.
6. Retention of Activity In Presence of Organic Matter
organic matter causes a moderate reduction in the activity of pine oil. As stated
previously, a fortified product (containing Phenolic) is adversely affected since organic
matter reduces Phenolic activity. |
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