APPLIED
AND
ENVIRONMENTAL MICROBIOLOGY, Aug. 1977, P. 129-134
Copyright © 1977 American Society for Microbiology
Vol. 34, No. 2 Printed in U.S.A.
Surface-Decontaminating Action of Glutaraldehyde in the Gas-Aerosol Phase AKE BOVALLIUS
AND
PER ANAS*
National Defence Research Institute, S-172 04 Sundbyberg, Sweden
Received for publication 1 February 1977
The surface disinfectant effect of glutaraldehyde in the gas-aerosol phase was investigated at different relative humidities and temperatures. At a gas-aerosol concentration of 15 to 20 mg/m3 and a relative humidity of about 80%, glutaraldehyde had a good disinfectant effect against both vegetative bacteria (decimal reduction time, GJ--
U
Organisms
26124-= 10 0 20 30 4/0
50
60
Time (min)
FIG. 2. Percentage of viable E. coli and B. cereus and the conditions in the chamber during a typical disinfection experiment with glutaraldehyde in the gas-aerosol phase. Symbols: (V) Viable E. coli, (0) viable B. cereus spores, (0) glutaraldehyde concentration in the gas-aerosol phase, (E) glutaraldehyde concentration in the gas phase, (V) relative humidity, (A) temperature. Added amount of glutaraldehyde, 250 mg/m3.
c
spores
E c 0 .--
--
(U
To check that E. coli and B. cereus spores representative for further studies, the disinfectant action on some vegetative organisms and other Bacillus spores was investigated. Approximative decimal reduction times of the tested organisms are listed in Table 1. All the tested vegetative bacteria had decimal reduction times of less than 5 min. The other spores tested were less resistant to glutaraldehyde than were B. cereus spores. Effect of relative humidity. Decimal reduction times for E. coli and for B. cereus spores were calculated from experiments performed at different relative humidities. The results (Fig. 3) show that the best disinfectant effect occurred at 80 to 90% relative humidity. At humidities approaching 100%, water condensation may occur, and, as glutaraldehyde dissolves very easily in water, it may be washed out from the air. This can explain the very low concentration of glutaraldehyde in the air and a were
0
'C 0 E
2010-
70 80 60 90 100 Relotive humidity (%/O) FIG. 3. Disinfectant action of glutaraldehyde in the gas-aerosol phase at different relative humidities . Symbols: (V) Decimal reduction times for E. coli, (0) decimal reduction times for B. cereus spores, (i) concentration of glutaraldehyde in the gas-aerosol phase (mean value and range during the experiments). Added amount of glutaraldehyde, 500 mg/ in3; temperature, 25 to 270C.
50
APPL. ENVIRON. MICROBIOL.
BOVALLIUS AND ANAS
132
low relative humidity, a considerable tailing was found in the time-survivor curves, and the decimal reduction time values were difficult to
tal series, different amounts of glutaraldehyde were distributed into the exposure chamber either by spraying or by boiling a water solution to dryness. The two ways of distribution resulted in approximately the same concentration in the chamber and also in the same disinfectant action. In these experiments addition of more than 1,000 mg of glutaraldehyde per m3 did not result in a final glutaraldehyde concentration in the gas-aerosol phase of more than 15 to 20 mg/m3 (Fig. 5), of which about 65 to 70% was in the gaseous phase. Thus, only a few percent of the added glutaraldehyde was found in the air. The residue must either have been precipitated in the chamber or, at least in the case of boiling, denatured into inactive, non-
evaluate. Effect of temperature. The increasing disinfectant effect at elevated temperatures was studied in three different experiments by conditioning the chamber to 10, 25, and 40°C before the glutaraldehyde was added (Fig. 4). The concentration in the chamber was about the same (15 to 20 mg/m3) in these tests, and, thus, the differences in the decimal reduction time values should be due to the temperature only. From that, a temperature coefficient of about 2 could be calculated. (The temperature coefficient, Q10, tells how much faster a disinfectant reaction proceeds when the temperature is ele- analyzable products. The pH of the sprayed solution does not seem vated by 10°C.) Effect of administration method and added to be as important as in liquid disinfection; in amount of glutaraldehyde. In two experimenI
100-
aE
E4) E
2
0
-
c .
U
50-
.)_ -4)
-
*0
-
520-
L-
c
cz
2
0
-
CD
-
0
0 4)
0
E
01
4)
40-
4i
_ 30-
-0
0 4-
(D
cW
20
-
10
'O
§ DE
X
0)
1
-
200-11,
5-
10-
-
E
CD
n u-'
L
0
f
10
25 40 Temperature ( C) FIG. 4. Disinfectant action of glutaraldehyde in the gas-aerosol phase at different temperatures. Symbols: (V) Decimal reduction times for E. coli, (0) decimal reduction times for B. cereus spores, (I ) concentration of glutaraldehyde in the gas-aerosol phase (mean value and range during the experiments). Added amount of glutaraldehyde, 500 mg/ mi3; relative humidity, 80%.
1000 2000 1500 560 Added omount of glutoroldehyde
( mg/m3 ) FIG. 5. Disinfectant action of glutaraldehyde in the gas-aerosol phase as a function of different added amounts. Symbols: (V) Decimal reduction times for E. coli, (0) decimal reduction times for B. cereus spores, (i) concentration of glutaraldehyde in the gas-aerosol phase (mean value and range during the experiments). Temperature, 24 to 27°C; relative humidity, 80%.
VOL. 34, 1977
GLUTARALDEHYDE IN THE GAS-AEROSOL PHASE
some comparative experiments it was shown that spraying a solution of glutaraldehyde buffered at pH 8 did not result in a significantly better disinfectant action than the use of an unbuffered acid solution. Comparison between glutaraldehyde and formaldehyde. Glutaraldehyde is more effective than formaldehyde against B. cereus spores and E. coli when they are compared at the same gas-aerosol concentration. Since glutaraldehyde is less volatile, more glutaraldehyde must be added to achieve a given concentration in the gas-aerosol phase, but, in spite of this fact, glutaraldehyde is a more effective disinfectant also when the added amounts are compared (Table 2).
DISCUSSION Glutaraldehyde in alkaline water solution has been shown to be a more effective disinfectant agent than a formaldehyde solution of the same concentration (1, 8). In the gas phase glutaraldehyde is also more effective than formnaldehyde, although the difference is not so pronounced. The effect of glutaraldehyde on surface contamination seems to be due to glutaraldehyde in the gas phase, and not to precipitated aerosol droplets, since in the latter case the pH of the sprayed solution should be of great importance. Spraying formaldehyde results in residues of water-insoluble paraformaldehyde, which often means that a long period of ventilation is needed after use. In the case of glutaraldehyde some precipitation also occurs, which can be removed either by thorough ventilation or by rinsing with water. Concerning other practical aspects, the properties seem to be about the same. Both glutaraldehyde and fornaldehyde have optimal actions at elevated relative humidities, and penetration ability, TABLE 2. Comparison of the surfacedecontaminating action of glutaraldehyde and formaldehyde in the gas-aerosol phase Decontaminating agent
Glutaral-
dehyde
Formaldehyde
Concn in Decimal reduction Added the gastime (min) amt (mg/ aerosol phase m3) E. i B. cereus 0 (mg/m3) spores 70 6 4 120-240 100 8 70
200 500 1,000
10 15 20
AND
ENVIRONMENTAL MICROBIOLOGY, Aug. 1977, P. 129-134
Copyright © 1977 American Society for Microbiology
Vol. 34, No. 2 Printed in U.S.A.
Surface-Decontaminating Action of Glutaraldehyde in the Gas-Aerosol Phase AKE BOVALLIUS
AND
PER ANAS*
National Defence Research Institute, S-172 04 Sundbyberg, Sweden
Received for publication 1 February 1977
The surface disinfectant effect of glutaraldehyde in the gas-aerosol phase was investigated at different relative humidities and temperatures. At a gas-aerosol concentration of 15 to 20 mg/m3 and a relative humidity of about 80%, glutaraldehyde had a good disinfectant effect against both vegetative bacteria (decimal reduction time, GJ--
U
Organisms
26124-= 10 0 20 30 4/0
50
60
Time (min)
FIG. 2. Percentage of viable E. coli and B. cereus and the conditions in the chamber during a typical disinfection experiment with glutaraldehyde in the gas-aerosol phase. Symbols: (V) Viable E. coli, (0) viable B. cereus spores, (0) glutaraldehyde concentration in the gas-aerosol phase, (E) glutaraldehyde concentration in the gas phase, (V) relative humidity, (A) temperature. Added amount of glutaraldehyde, 250 mg/m3.
c
spores
E c 0 .--
--
(U
To check that E. coli and B. cereus spores representative for further studies, the disinfectant action on some vegetative organisms and other Bacillus spores was investigated. Approximative decimal reduction times of the tested organisms are listed in Table 1. All the tested vegetative bacteria had decimal reduction times of less than 5 min. The other spores tested were less resistant to glutaraldehyde than were B. cereus spores. Effect of relative humidity. Decimal reduction times for E. coli and for B. cereus spores were calculated from experiments performed at different relative humidities. The results (Fig. 3) show that the best disinfectant effect occurred at 80 to 90% relative humidity. At humidities approaching 100%, water condensation may occur, and, as glutaraldehyde dissolves very easily in water, it may be washed out from the air. This can explain the very low concentration of glutaraldehyde in the air and a were
0
'C 0 E
2010-
70 80 60 90 100 Relotive humidity (%/O) FIG. 3. Disinfectant action of glutaraldehyde in the gas-aerosol phase at different relative humidities . Symbols: (V) Decimal reduction times for E. coli, (0) decimal reduction times for B. cereus spores, (i) concentration of glutaraldehyde in the gas-aerosol phase (mean value and range during the experiments). Added amount of glutaraldehyde, 500 mg/ in3; temperature, 25 to 270C.
50
APPL. ENVIRON. MICROBIOL.
BOVALLIUS AND ANAS
132
low relative humidity, a considerable tailing was found in the time-survivor curves, and the decimal reduction time values were difficult to
tal series, different amounts of glutaraldehyde were distributed into the exposure chamber either by spraying or by boiling a water solution to dryness. The two ways of distribution resulted in approximately the same concentration in the chamber and also in the same disinfectant action. In these experiments addition of more than 1,000 mg of glutaraldehyde per m3 did not result in a final glutaraldehyde concentration in the gas-aerosol phase of more than 15 to 20 mg/m3 (Fig. 5), of which about 65 to 70% was in the gaseous phase. Thus, only a few percent of the added glutaraldehyde was found in the air. The residue must either have been precipitated in the chamber or, at least in the case of boiling, denatured into inactive, non-
evaluate. Effect of temperature. The increasing disinfectant effect at elevated temperatures was studied in three different experiments by conditioning the chamber to 10, 25, and 40°C before the glutaraldehyde was added (Fig. 4). The concentration in the chamber was about the same (15 to 20 mg/m3) in these tests, and, thus, the differences in the decimal reduction time values should be due to the temperature only. From that, a temperature coefficient of about 2 could be calculated. (The temperature coefficient, Q10, tells how much faster a disinfectant reaction proceeds when the temperature is ele- analyzable products. The pH of the sprayed solution does not seem vated by 10°C.) Effect of administration method and added to be as important as in liquid disinfection; in amount of glutaraldehyde. In two experimenI
100-
aE
E4) E
2
0
-
c .
U
50-
.)_ -4)
-
*0
-
520-
L-
c
cz
2
0
-
CD
-
0
0 4)
0
E
01
4)
40-
4i
_ 30-
-0
0 4-
(D
cW
20
-
10
'O
§ DE
X
0)
1
-
200-11,
5-
10-
-
E
CD
n u-'
L
0
f
10
25 40 Temperature ( C) FIG. 4. Disinfectant action of glutaraldehyde in the gas-aerosol phase at different temperatures. Symbols: (V) Decimal reduction times for E. coli, (0) decimal reduction times for B. cereus spores, (I ) concentration of glutaraldehyde in the gas-aerosol phase (mean value and range during the experiments). Added amount of glutaraldehyde, 500 mg/ mi3; relative humidity, 80%.
1000 2000 1500 560 Added omount of glutoroldehyde
( mg/m3 ) FIG. 5. Disinfectant action of glutaraldehyde in the gas-aerosol phase as a function of different added amounts. Symbols: (V) Decimal reduction times for E. coli, (0) decimal reduction times for B. cereus spores, (i) concentration of glutaraldehyde in the gas-aerosol phase (mean value and range during the experiments). Temperature, 24 to 27°C; relative humidity, 80%.
VOL. 34, 1977
GLUTARALDEHYDE IN THE GAS-AEROSOL PHASE
some comparative experiments it was shown that spraying a solution of glutaraldehyde buffered at pH 8 did not result in a significantly better disinfectant action than the use of an unbuffered acid solution. Comparison between glutaraldehyde and formaldehyde. Glutaraldehyde is more effective than formaldehyde against B. cereus spores and E. coli when they are compared at the same gas-aerosol concentration. Since glutaraldehyde is less volatile, more glutaraldehyde must be added to achieve a given concentration in the gas-aerosol phase, but, in spite of this fact, glutaraldehyde is a more effective disinfectant also when the added amounts are compared (Table 2).
DISCUSSION Glutaraldehyde in alkaline water solution has been shown to be a more effective disinfectant agent than a formaldehyde solution of the same concentration (1, 8). In the gas phase glutaraldehyde is also more effective than formnaldehyde, although the difference is not so pronounced. The effect of glutaraldehyde on surface contamination seems to be due to glutaraldehyde in the gas phase, and not to precipitated aerosol droplets, since in the latter case the pH of the sprayed solution should be of great importance. Spraying formaldehyde results in residues of water-insoluble paraformaldehyde, which often means that a long period of ventilation is needed after use. In the case of glutaraldehyde some precipitation also occurs, which can be removed either by thorough ventilation or by rinsing with water. Concerning other practical aspects, the properties seem to be about the same. Both glutaraldehyde and fornaldehyde have optimal actions at elevated relative humidities, and penetration ability, TABLE 2. Comparison of the surfacedecontaminating action of glutaraldehyde and formaldehyde in the gas-aerosol phase Decontaminating agent
Glutaral-
dehyde
Formaldehyde
Concn in Decimal reduction Added the gastime (min) amt (mg/ aerosol phase m3) E. i B. cereus 0 (mg/m3) spores 70 6 4 120-240 100 8 70
200 500 1,000
10 15 20
