APPENDIX D— 31 
particularly those having complex optical 
and electronic components. 
Chemicals with decontaminant properties 
are. lor the most part, available as powders, 
crystals, and liquid concentrates. These may 
be added to tap water for application as sur- 
face decontaminants, and some, when added 
la sufiSclent quantity, find use as decontam- 
inants of bulk liquid wastes. Chemical de- 
contaminants that are^aseous at room tem- 
peratures are useful as space-penetrating de- 
contaminants. Others become gases at rea- 
sonably elevated temperatures and can act 
as either aqueous surface or gaseous space- 
penetrating decontaminants. 
Inactivation of microorganisms by chemi- 
cal decontaminants may occur in one or more 
of the following ways ; 
1. Coagulation and denaturation of protein. 
2. Lysis. 
3. Binding to enzymes, or inactivation of an 
essential enzyme by either oxidation, bind- 
ing, or destruction of enzyme substrate. 
The relative resistance to the action of chemi- 
cal decontaminants can be substantially al- 
tered by such factors as: concentration of ac- 
tive ingredient, duration of contact, pH, tem- 
perature, humidity, and presence of extrinsic 
organic matter. Depending upon how these 
factors are manipulated, the degree of suc- 
cess achieved, with chemical decontaminants 
may range from minimal Inactivation of tar- 
get microorganisms to an indicated sterility 
within the limits of sensitivity of the assay 
systems employed. 
There are dozens of decohtamlnants availa- 
ble \mder a wide variety of trade names. In 
general, these^decontaminants can be cleissl- 
fied as halogens, acids or alkalies, heavy metal 
salts, quaternary ammonium compounds, 
phenolic compounds, aldehydes, ketones, al- 
cohols, and amines. Unfortunately, the more 
active the decontaminant the more likely it 
will possess undesirable characteristics. For 
example, peracetic acid is a fast-acting, uni- 
versal decontaminant. However, in the con- 
centrated state it is a hazardous compound 
that can readily decompose with explosive 
violence. When diluted for use, it has a short 
half-life, produces strong, pungent. Irritating 
odors, and is extremely corrosive to metals. 
Nevertheless, it is such an outstanding de- 
contaminant that it is commonly used in 
germ-free animal studies despite these un- 
desirable characteristics. 
The halogens are probably the second most 
active group of decontaminants. Chlorine, 
Iodine, bromine, and fluorine will rapidly kill 
bacterial spores, viruses, rickettsiae, £ind 
fungi. These decontaminants are effective 
over a wide range of temperatures. In fact, 
chlorine has been shown to be effective at 
—40 P. (On the other hand, phenols and 
formaldehyde have high temperature coef- 
ficients) . The halogens have several undesira- 
ble features. They readily combine with pro- 
tein, so that an excess of the halogen must 
be used if proteins are present. Also, the halo- 
gens are relatively unstable so that fresh 
solutions must be prepared at frequent in- 
tervals. Finally, the halogens corrode metals. 
A number of manufacturers of decontami- 
nants have treated the halogens to remove 
some of the undesirable features. For exam- 
ple. sodium hypochlorite reacts with p-tolu- 
enesulfonamlde to form Chloramine T, and 
iodine reacts with certain surface-active 
agents to form the popular lodophors. These 
“tamed” halogens are stable, non-toxic, odor- 
less, and relatively noncorrosive to metals. 
However, the halogens are highly reactive 
elements, and, because they are reactive they 
are good germicides. When a halogen acts 
as a decontaminant, free halogen la the ef- 
fective agent. Rising the pH or combining 
the halogen with other compotinds to de- 
crease the corrosive effect will also decrease 
the germicidal power. A trade-off situation 
occurs. 
Ineffectiveness of a decontaminant is due 
primarily to the failure of the decontaminant 
to contact the microorganisms rather than 
failure of the decontaminant to act. If one 
places an item in a liquid decontaminant, one 
can see that the item is covered with tiny 
bubbles. Of course, the area under the 
bubbles is dry, and microorganisms In these 
dry areas will not be affected by the decon- 
taminant. Also, If there are spots of grease, 
rust or dirt on the object, microorganisms 
under these protective coatings will not be 
contacted by the decontaminant. Scrubbing 
an Item when immersed in a decontaminant 
is helpful, and a decontaminant should have, 
and most do have, incorporated surface- 
active agents. 
F. PropeTties of Some Common Decontam- 
inants 
1. Alcohol. Ethyl or isopropyl alcohol in a 
concentration of 70-85% by weight is often 
used. Alcohols denature proteins and are 
somewhat slow in their germicidal action. 
However, they are effective decontaminants 
against lipid-containing viruses. 
2. Ether and Chloroform. These compounds 
are not ordinarily used as decontaminants, 
but they do demonstrate the fact that llpid- 
cqntalning viruses are Inactivated by these 
organic solvents, whereas non-lipid-contain- 
ing viruses are quite resistant. 
3. Formaldehyde. Formaldehyde for use as 
a decontaminant is usually marketed as a 
solution of about 37 % concentration referred 
to as formalin or as a solid polymerized com- 
pound called paraformaldehyde. Formalde- 
hyde in a concentration of 6% active in- 
gredient is an effective liquid decontaminant. 
It loses considerable activity at refrigeration 
tempyeratvu-es and the pungent, irritating 
odors make formaldehyde solutions difficult 
to use In the laboratory. Formaldehyde vapor 
generated from formaldehyde solution is an 
effective space decontaminant for decontam- 
inating rooms or buildings, but in the vapor 
state with water it tends to polymerize out 
on surfaces to form paraformaldehyde, which 
is persistent and unpleasant. Formaldehyde 
gas can be liberated by heating paraformalde- 
hyde to depolymerize it. In the absence of 
high moisture content in the air, formalde- 
hyde released in the gaseous state forms less 
polymerized residues on surfaces and less 
time is required to Clear treated areas of 
fumes than formaldehyde released in the 
vapor state. 
4. Phenol. Phenol Itself is not often used 
as a decontaminant. The odor is somewhat 
unpleasant and a sticky, gummy residue re- 
mains on treated surfaces. This is especially 
true during steam sterilization. Although 
phenol Itself may not be In widespread use, 
phenol homologs and phenolic compounds 
are basic to a number of popular decontam- 
inants. The phenolic compounds are effective 
decontaminants against some viruses, ric- 
kettsiae, fimgl and vegetative bacteria. The 
phenollcs are not effective in ordinary usage 
against bacterial spores. 
5. Quaternary Ammonium Compounds or 
Quats. After 30 years of testing and use, there 
is still a considerable controversy about the 
efficacy of the Quats as decontaminants. 
These cationic detergents are strongly sur- 
face-active and are effective against llpld- 
contalnlng viruses. The Quats will attach to 
protein so that dilute solutions of Quats 
will quickly lose effectiveness In the presence 
of proteins. The Quats tend to clump micro- 
organisms and are neutralized by anionic de- 
tergents, such as soap. The Quats have the 
advantages of being nontoxic, odorless, non- 
stalnlng, noncorrosive to metals, stable, and 
Inexpensive. 
6. Chlorine. This halogen Is a universal 
decontaminant active against all micro- 
organisms, including bacterial spores. Chlo- 
rine combines with protein and rapidly de- 
creases in concentration In Its presence. Free, 
available chlorine is an active element. It 
is a strong oxidizing agent, corrosive to 
metals. Chlorine solutions will gradually lose 
strength so that fresh solutions must be pre- 
pared frequently. Sodium hypochlorite is 
usually used as a base for chlorine decon- 
taminants. An excellent decontaminant can 
be prepared from household or laundry 
bleach. These bleaches usually contain 5.25 
percent available chlorine or 52,500 ppm. If 
one dilutes them to 1 to ioo, the solution will 
contain 525 ppm of available chlorine, and, 
if a nonionic detergent such as Naccanol is 
added In a concentration of about 0.7 per- 
cent, a very good decontaminant Is created. 
7. Iodine. The characteristics of chlorine 
and iodine are similar. One of the most popu- 
lar groups of decontaminants used In the 
laboratory is the lodophors, and Wescodyne 
Is perhaps the most popular. The range of 
dilution of Wescodyne recommended by the 
manufacturer is 1 oz. in 6 gal. of water giving 
25 ppm of available iodine to 3 oz. In 5 gal. 
giving 775 ppm. At 75 ppm, the concentra- 
tion of free iodine is .0075 percent. This small 
amount can be rapidly taken up by any ex- 
traneous protein present. Clean surfaces or 
clear water can be effectively treated by 75 
ppm available Iodine, but difficulties may be 
experienced if any appreciable amount of 
protein is present. For bacterial spores, a 
dilution of 1 to 40 giving 750 ppm Is recom- 
mended by the manufacturer. For washing 
the hands, it Is recommeflded that Wesco- 
dyne be diluted 1 to 10 or 10% In 50% ethyl 
alcohol (a reasonably good decontaminant 
Itself) which will give 1,600 ppm of avail- 
able Iodine, at which concentration rela- 
tively rapid Inactivation of any and all mi- 
croorganisms will occur. 
G. Vapors and Gases 
The use of formaldehyde as a vapor or gas 
has already been discussed. Other chemical 
decontaminants which have been used this 
way Included ethylene oxide, peracetic acid, 
beta-propiolactone (BPL), methyl bromide, 
and ethylene amine. When these can be used 
in closed systems and under controlled con- 
ditions of temperature and humidity, ex- 
cellent decontamination can be obtained. 
Residues from ethylene oxide must be re- 
moved by aeration; but otherwise It is con- 
venient to use, versatile, and noncorrosive. 
Peracetic acid Is corrosive for metals and 
rubber. BPL In the vapor form acts rapidly 
against bacteria, rickettsiae, and viruses. It 
has a half-life of 3.5 hours when mixed with 
water. Is easily neutralized with water, and 
lends itself to removal by aeration. The Na- 
tional Institutes of Health does not recom- 
mend BPL as a decontaminant because It 
has been identified as a suspect carcinogen. 
H. Residual Action of Decontaminants 
As noted in the preceding discussion of 
decontaminant properties, many of the 
chemical decontaminants often have residual 
properties that may be considered a desirable 
feature in terms of aiding In the control of 
background contamination. One Is cau- 
tioned, however, to consider residual prop- 
erties carefully. Ethylene oxide used to 
sterilize laboratory shoes can leave residues 
which cause skin irritation. Animal cell cul- 
tures, as well as viruses of interest, are also 
inhibited or Inactivated by the decontami- 
nants persisting after routine cleaning pro- 
cedures. Therefore, reusable items that are 
routinely held in liquid decontaminant prior 
to autoclaving and cleaning should receive 
particular attention In rinse cycles. Sim- 
ilarly, during general area decontamination 
with gases or vapors. It may be necessary 
to protect new and used clean Items by re- 
moving them from the area or by enclosing 
