Biocidal compositions and use thereof containing a synergistic mixture of 3-iodo-2-propynyl-butyl carbamate and 3,4-dichloro-1,2-dithiol-3-one

A bactericidal composition and method for inhibiting and controlling the growth of the capsulated, facultative bacterium, Klebsiella pneumoniae, are disclosed. The composition comprises an amount, effective for the intended purpose of 3-iodo-2-propynylbutyl carbamate and 3,4-dichloro-1,2-dithiol-3-one. The method comprises administering between about 0.1 to about 200 parts of this combined treatment (based on one million parts of the desired aqueous system) to the particular water containing system for which treatment is desired.

BACKGROUND OF THE INVENTION 
The formation of slimes by microorganisms is a problem that is encountered 
in many aqueous systems. For example, the problem is not only found in 
natural waters such as lagoons, lakes, ponds, etc., and confined waters as 
in pools, but also in such industrial systems as cooling water systems, 
air washer systems and pulp and paper mill systems. All possess conditions 
which are conductive to the growth and reproduction of slime-forming 
microorganisms. In both once-through and recirculating cooling systems, 
for example, which employ large quantities of water as a cooling medium, 
the formation of slime by microorganisms is an extensive and constant 
problem. 
Airborne organisms are readily entrained in the water from cooling towers 
and find this warm medium an ideal environment for growth and 
multiplication. Aerobic and heliotropic organisms flourish on the tower 
proper while other organisms colonize and grow in such areas as the tower 
sump and the piping and passages of the cooling system. The slime 
formation not only aids in the deterioration of the tower structure in the 
case of wooden towers, but also promotes corrosion when it deposits on 
metal surfaces. Slime carried through the cooling system plugs and fouls 
lines, valves, strainers, etc., and deposits on heat exchange surfaces. In 
the latter case, the impedance of heat transfer can greatly reduce the 
efficiency of the cooling system. 
In pulp and paper mill systems, slime formed by microorganisms is commonly 
encountered and causes fouling, plugging, or corrosion of the system. The 
slime also becomes entrained in the paper produced to cause breakouts on 
the paper machines, which results in work stoppages and the loss of 
production time. The slime is also responsible for unsightly blemishes in 
the final product, which result in rejects and wasted output. 
The previously discussed problems have resulted in the extensive 
utilization of biocides in cooling water and pulp and paper mill systems. 
Materials which have enjoyed widespread use in such applications include 
chlorine, chlorinated phenols, organo-bromines, and various organo-sulfur 
compounds. All of these compounds are generally useful for this purpose 
but each is attended by a variety of impediments. For example, 
chlorination is limited both by its specific toxicity for slime-forming 
organisms at economic levels and by the tendency of chlorine to react, 
which results in the expenditure of the chlorine before its full biocidal 
function is achieved. Other biocides are attended by odor problems and 
hazards with respect to storage, use or handling which limit their 
utility. To date, no one compound or type of compound has achieved a 
clearly established predominance with respect to the applications 
discussed. Likewise, lagoons, ponds, lakes, and even pools, either used 
for pleasure purposes or used for industrial purposes for the disposal and 
storage of industrial wastes, become, during the warm weather, besieged by 
slime due to microorganism growth and reproduction. In the case of 
industrial storage or disposal of industrial materials, the microorganisms 
cause additional problems which must be eliminated prior to the materials' 
use or disposal of the waste. 
Naturally, economy is a major consideration with respect to all of these 
biocides. Such economic considerations attach to both the cost of the 
biocide and the expense of its application. The cost performance index of 
any biocide is derived from the basic cost of the material, its 
effectiveness per unit of weight, the duration of its biocidal or 
biostatic effect in the system treated, and the ease and frequency of its 
addition to the system treated. To date, none of the commercially 
available biocides has exhibited a prolonged biocidal effect. Instead, 
their effectiveness is rapidly reduced as a result of physical conditions 
such as temperature, association with ingredients contained by the system 
toward which they exhibit an affinity or substantivity, etc., with a 
resultant restriction or elimination of their biocides effectiveness, or 
by dilution. 
As a consequence, the use of such biocides involves their continuous or 
frequent addition to systems to be treated and their addition to multiple 
points or zones in the systems to be treated. Accordingly, the cost of the 
biocides and the labor cost of applying it are considerable. In other 
instances, the difficulty of access to the zone in which slime formation 
is experienced precludes the effective use of a biocide. For example, if 
in a particular system there is no access to an area at which slime 
formation occurs the biocide can only be applied at a point which is 
upstream in the flow system. However, the physical or chemical conditions, 
e.g., chemical reactivity, thermal degradation, etc., which exist between 
the point at which the biocide may be added to the system and the point at 
which its biocidal effect is desired render the effective use of a biocide 
impossible. 
Similarly, in a system experiencing relatively slow flow, such as a paper 
mill, if a biocide is added at the beginning of the system, its biocidal 
effect may be completely dissipated before it has reached all of the 
points at which this effect is desired or required. As a consequence, the 
biocide must be added at multiple points, and even then a diminishing 
biocidal effect will be experienced between one point of addition to the 
system and the next point downstream at which the biocides may be added. 
In addition to the increased cost of utilizing and maintaining multiple 
feed points, gross ineconomies with respect to the cost of the biocide are 
experienced. Specifically, at each point of addition, an excess of the 
biocide is added to the system in order to compensate for that portion of 
the biocide which will be expended in reacting with other constituents 
present in the system or experience physical changes which impair its 
biocidal activity. 
SUMMARY OF THE INVENTION 
The biocidal compositions of the present invention comprise, as active 
ingredients, 1) 3-iodo-2-propynyl-butyl carbamate (IPBC) and 2) 
3,4-dichloro-1,2-dithiol-3-one (DCDT). These constituents are commercially 
available. The synergistic effect obtained by combining IPBC and DCDT has 
not been previously disclosed.

DETAILED DESCRIPTION OF THE INVENTION 
Surprisingly, the present inventors have found that mixtures of IPBC and 
DCDT are especially efficacious in controlling the growth of bacterial 
microbes, specifically the Klebsiella pneumoniae species. This particular 
species is a member of the capsulated, facultative class of bacterial and 
is generally present in air, water and soil. These bacterial continually 
contaminate open cooling systems and pulping and papermaking systems and 
are among the most common slime formers. The slime may be viewed as being 
a mass of agglomerated cells stuck together by the cementing action of the 
gelatinous polysaccharide or proteinaceious secretions around each cell. 
The slimy mass entraps other debris, restricts water flow and heat 
transfer, and may serve as s site for corrosion. 
The fact that the Klebsiella species used in the tests is a facultative 
species is important as, by definition, such bacteria may thrive under 
either aerobic or anaerobic conditions. Accordingly, by reason of 
demonstrated efficacy in the growth inhibition of this particular species, 
one can expect similar growth inhibition attributes when other aerobic or 
anaerobic bacterial species are encountered. It is also expected that 
these compositions will exhibit similar growth inhibition attributes when 
fungi and algae species are encountered. 
In accordance with the present invention, the combined IPBC and DCDT 
treatment may be added to the desired aqueous system in need of a biocidal 
treatment, in an amount of from about 0.1 to about 200 parts of the 
combined treatment to one million parts (by weight) of the aqueous medium. 
Preferably, about 5 to about 50 parts of the combined treatment per one 
million parts (by weight) of the aqueous medium is added. 
The combined treatment is added, for example, to cooling water systems, 
paper and pulp mill systems, pools, ponds, lagoons, lakes, etc., to 
control the formation of bacterial microorganisms, which may be contained 
by, or which may become entrained in, the system to be treated. It has 
been found that the compositions and methods of utilization of the 
treatment are efficacious in controlling the facultative bacterium, 
Klebsiella pneumoniae, which may populate these systems. It is thought 
that the combined treatment composition and method of the present 
invention will also be efficacious in inhibiting and controlling all types 
of aerobic and anaerobic bacteria. 
Surprisingly, it has been found that when the ingredients are mixed, in 
certain instances, the resulting mixtures possess a higher degree of 
bactericidal activity than that of the individual ingredients comprising 
the mixture. Accordingly, it is possible to produce a highly efficacious 
bactericide. Because of the enhanced activity of the mixture, the total 
quantity of the bacterial treatment may be reduced. In addition, the high 
degree of bactericidal effectiveness which is provided by each of the 
ingredients may be exploited without use of higher concentrations of each. 
The following experimental data were developed. It is to be remembered that 
the following examples are to be regarded solely as being illustrative and 
not as restricting the scope of the invention. 
DESCRIPTION OF PREFERRED EMBODIMENT 
IPBC and DCDT were added in varying ratios and over a wide range of 
concentrations to a liquid nutrient medium which was subsequently 
inoculated with a standard volume of a suspension of the facultative 
bacterium Klebsiella pneumoniae. Growth was measured by determining the 
amount of radioactivity accumulated by the cells when 14C-glucose was 
added as the sole source of carbon in the nutrient medium. The effect of 
the biocide chemicals, alone and in combination, is to reduce the rate and 
amount of 14C incorporation into the cells during incubation, as compared 
to controls not treated with chemicals. Additions to the biocides, alone 
and in varying combinations and concentrations, were made according to the 
accepted "checkerboard" technique described by M. T. Kelley and J. M. 
Matsen, Antimicrobial Agents and Chemotherapy, 9:440 (1976). Following a 
two hour incubation, the amount of radioactivity incorporated in the cells 
was determined by counting (14C liquid scintillation procedures) for all 
treated and untreated samples. The percent reduction of each treated 
sample was calculated from the relationship: 
##EQU1## 
Plotting the % reduction of 14C level against the concentration of each 
biocide acting alone results in a dose-response curve, from which the 
biocide dose necessary to achieve any given % reduction can be 
interpolated. 
Synergism was determined by the method of calculation described by F. C. 
Kyll, P. C. Eisman, H. D. Sylwestrowicz and R. L. Mayer, Applied 
Microbiology 9, 538 (1961) using the relationship: 
##EQU2## 
where .sup.Q a=quantity of compound A, acting alone, producing an end 
point 
.sup.Q b=quantity of compound B, acting alone, producing an end point 
.sup.Q A=quantity of compound A in mixture, producing an end point 
.sup.Q B=quantity of compound B in mixture, producing an end point 
The end point used in the calculations is the % reduction caused by each 
mixture of A and B. .sup.Q A and .sup.Q B are the individual 
concentrations in the A/B mixture causing a given % reduction. .sup.Q a 
and .sup.Q b are determined by interpolation from the respective 
dose-response curves of A and B as those concentrations of A and B acting 
alone which produce the same % reduction as each specific mixture 
produced. 
Dose-response curves for each active acting alone were determined by linear 
regression analysis of the dose-response data. Data was fitted to a curve 
represented by the equation shown with each data set. After linearizing 
the data, the contributions of each biocide component in the biocide 
mixtures to the inhibition of radioisotope uptake were determined by 
interpolation with the dose-response curve of the respective biocide. If, 
for example, quantities of .sup.Q A plus .sup.Q B are sufficient to give a 
50% reduction in 14C content, .sup.Q a and .sup.Q b are those quantities 
of A or B acting alone, respectively, found to give 50% reduction in 14C 
content. A synergism index (SI) is calculated for each combination of A 
and B. 
Where the SI is less than 1, synergism exists. Where the SI=1, additivity 
exists. Where SI is greater than 1, antagonism exists. 
The data in the following tables come from treating Klebsiella pneumoniae, 
a common nuisance bacterial type found in industrial cooling waters and in 
pulping and paper making systems, with varying ratios and concentrations 
of IPBC and DCDT. Shown for each combination is the % reduction of 14C 
content (% I), the calculated SI, and the weight ratio of IPBC and DCDT. 
TABLE I 
______________________________________ 
IPBC vs. DCDT 
ppm ppm Ratio 
IPBC.sup.1 
DCDT.sup.2 
IPBC:DCDT % I SI 
______________________________________ 
50 0 100:0 94 
25 0 100:0 90 
12.5 0 100:0 80 
6.25 0 100:0 63 
3.13 0 100:0 46 
1.56 0 100:0 34 
0 10 0:100 98 
0 5 0:100 98 
0 2.5 0:100 97 
0 1.25 0:100 71 
0 0.625 0:100 44 
0 0.313 0:100 29 
50 10 5.00:1 99 3.15 
25 10 2.50:1 99 2.60 
12.5 10 1.25:1 99 2.32 
6.25 10 1:1.60 99 2.17 
3.13 10 1:3.19 99 2.12 
1.56 10 1:6.41 99 2.08 
50 5 10.0:1 99 2.13 
25 5 5.00:1 99 1.58 
12.5 5 2.50:1 99 1.30 
6.25 5 1.25:1 99 1.16 
3.13 5 1:1.60 99 1.09 
1.56 5 1:3.21 99 1.05 
50 2.5 20.0:1 99 1.63 
25 2.5 10.0:1 98 1.08 
12.5 2.5 5.00:1 98 0.80* 
6.25 2.5 2.50:1 98 0.68* 
3.13 2.5 1.25:1 97 0.63* 
1.56 2.5 1:1.60 97 0.58* 
50 1.25 40.0:1 98 1.44 
25 1.25 20.0:1 95 0.98 
12.5 1.25 10.0:1 91 0.78* 
6.25 1.25 5.00:1 83 0.80* 
3.13 1.25 2.50:1 74 0.92* 
1.56 1.25 1.25:1 68 1.02 
50 0.625 80.0:1 95 1.50 
25 0.625 40.0:1 91 1.00 
12.5 0.625 20.0:1 84 0.85* 
6.25 0.625 10.0:1 70 1.04 
3.13 0.625 5.01:1 57 1.30 
1.56 0.625 2.50:1 52 1.23 
50 0.313 160:1 94 1.49 
25 0.313 79.9:1 91 0.94* 
12.5 0.313 39.9:1 83 0.76* 
6.25 0.313 19.97:1 69 0.90* 
3.13 0.313 10.0:1 54 1.11 
1.56 0.313 4.99:1 40 1.45 
______________________________________ 
.sup.1 product containing 17% actives IPBC 
.sup.2 product containing 20% actives DCDT 
TABLE II 
______________________________________ 
IPBC vs. DCDT 
ppm ppm Ratio 
IPBC.sup.1 
DCDT.sup.2 
IPBC:DCDT % I SI 
______________________________________ 
50 0 100:0 92 
25 0 100:0 87 
12.5 0 100:0 71 
6.25 0 100:0 48 
3.13 0 100:0 26 
1.56 0 100:0 14 
0 10 0:100 99 
0 5 0:100 99 
0 2.5 0:100 90 
0 1.25 0:100 39 
0 0.625 0:100 21 
0 0.313 0:100 14 
50 10 5.00:1 99 2.76 
25 10 2.50:1 99 2.23 
12.5 10 1.25:1 99 1.97 
6.25 10 1:1.60 99 1.86 
3.13 10 1:3.19 99 1.80 
1.56 10 1:6.41 99 1.76 
50 5 10.0:1 99 1.89 
25 5 5.00:1 99 1.37 
12.5 5 2.50:1 99 1.12 
6.25 5 1.25:1 99 0.99 
3.13 5 1:1.60 99 0.93* 
1.56 5 1:3.21 98 0.92* 
50 2.5 20.0:1 99 1.47 
25 2.5 10.0:1 99 0.96 
12.5 2.5 5.00:1 98 0.72* 
6.25 2.5 2.50:1 94 0.66* 
3.13 2.5 1.25:1 92 0.62* 
1.56 2.5 1:1.60 90 0.61* 
50 1.25 40.0:1 95 1.48 
25 1.25 20.0:1 90 1.04 
12.5 1.25 10.0:1 81 0.91* 
6.25 1.25 5.00:1 69 0.96 
3.13 1.25 2.50:1 54 1.23 
1.56 1.25 1.25:1 44 1.44 
50 0.625 80.0:1 92 1.48 
25 0.625 40.0:1 86 1.02 
12.5 0.625 20.0:1 78 0.82* 
6.25 0.625 10.0:1 60 0.98 
3.13 0.625 5.01:1 42 1.23 
1.56 0.625 2.50:1 32 1.31 
50 0.313 160:1 92 1.44 
25 0.313 79.9:1 85 0.99 
12.5 0.313 39.9:1 76 0.75* 
6.25 0.313 19.97:1 58 0.85* 
3.13 0.313 10.0:1 38 1.10 
1.56 0.313 4.99:1 23 1.24 
______________________________________ 
.sup.1 product containing 17% actives IPBC 
.sup.2 product containing 20% actives DCDT 
TABLE III 
______________________________________ 
IPBC vs. DCDT 
ppm ppm Ratio 
IPBC.sup.1 
DCDT.sup.2 
IPBC:DCDT % I SI 
______________________________________ 
50 0 100:0 87 
25 0 100:0 79 
12.5 0 100:0 63 
6.25 0 100:0 57 
3.13 0 100:0 34 
1.56 0 100:0 13 
0 10 0:100 98 
0 5 0:100 98 
0 2.5 0:100 73 
0 1.25 0:100 31 
0 0.625 0:100 13 
0 0.313 0:100 8 
50 10 5.00:1 98 2.27 
25 10 2.50:1 98 1.85 
12.5 10 1.25:1 98 1.66 
6.25 10 1:1.60 98 1.55 
3.13 10 1:3.19 98 1.51 
1.56 10 1:6.41 98 1.49 
50 5 10.0:1 98 1.53 
25 5 5.00:1 98 1.13 
12.5 5 2.50:1 98 0.93* 
6.25 5 1.25:1 98 0.83* 
3.13 5 1:1.60 98 0.78* 
1.56 5 1:3.21 98 0.76* 
50 2.5 20.0:1 97 1.22 
25 2.5 10.0:1 95 0.88* 
12.5 2.5 5.00:1 88 0.83* 
6.25 2.5 2.50:1 85 0.73* 
3.13 2.5 1.25:1 80 0.76* 
1.56 2.5 1:1.60 77 0.75* 
50 1.25 40.0:1 91 1.34 
25 1.25 20.0:1 85 1.02 
12.5 1.25 10.0:1 76 0.92* 
6.25 1.25 5.00:1 63 1.05 
3.13 1.25 2.50:1 52 1.14 
1.56 1.25 1.25:1 47 1.13 
50 0.625 80.0:1 89 1.35 
25 0.625 40.0:1 73 1.48 
12.5 0.625 20.0:1 70 0.95* 
6.25 0.625 10.0:1 55 1.05 
3.13 0.625 5.01:1 37 1.41 
1.56 0.625 2.50:1 33 1.15 
50 0.313 160:1 89 1.31 
25 0.313 79.9:1 80 0.99 
12.5 0.313 39.9:1 69 0.88* 
6.25 0.313 19.97:1 52 1.00 
3.13 0.313 10.0:1 37 1.14 
1.56 0.313 4.99:1 29 0.96 
______________________________________ 
.sup.1 product containing 17% actives IPBC 
.sup.2 product containing 20% actives DCDT 
Asterisks in the SI column indicate synergistic combinations in accordance 
with the Kull method supra. 
In Tables I through III, differences seen between the replicates are due to 
normal experimental variance. 
In accordance with Tables I-III supra., unexpected results occurred more 
frequently within the product ratios of IPBS to DCDT of from about 1:3.2 
to 80:1. Since the IPBC product contains about 17% active biocidal 
component and the DCDT product contains about 20% active biocidal 
component, when based on the active biocidal component, unexpected results 
appear more frequently within the range of active component of IPBC:DCDT 
of about 1:3.8 to 68:1. At present, it is most preferred that any 
commercial product embodying the invention comprises a weight ratio of 
active component of about 1:1 IPBC:DCDT. 
While this invention has been described with respect to particular 
embodiments thereof, it is apparent that numerous other forms and 
modifications of this invention will be obvious to those skilled in the 
art. The appended claims and this invention generally should be construed 
to cover all such obvious forms and modifications which are within the 
true spirit and scope of the present invention.