MICROBICIDAL COMPOSITION

Abstract

A synergistic microbicidal composition comprising a hydroxymethyl-substituted phosphorus compound and nitrate, a method for inhibiting the growth of microorganisms in an aqueous medium.

Claims

1. A synergistic microbicidal composition comprising a hydroxymethyl-substituted phosphorus compound and nitrate.

2. The synergistic microbicidal composition of claim 1 wherein the ratio of hydroxymethyl-substituted phosphorus compound to nitrate is 32:1 to 1:16.

3. The synergistic microbiocidal composition of claim 1 wherein the hydroxymethyl substituted phosphorus compound is tetrakis(hydroxymethyl) phosphonium sulfate.

4. The synergistic microbicidal composition of claim 3 wherein the ratio of tetrakis(hydroxymethyl) phosphonium sulfate to nitrate is 32:1 to 1:16.

5. A method for controlling the growth of microorganisms in an aqueous medium; the method comprising adding to the aqueous medium the synergistic microbiocidal composition of claim 1.

Description

EXAMPLE

[0010] Inside an anaerobic chamber (Bactron anaerobic chamber), a deoxygenated sterile salt solution (3.12 g of NaCl, 0.13 g of NaHCO.sub.3, 0.17 g of Na.sub.2SO.sub.4, 47.70 mg of KC1, 72.00 mg of CaCl.sub.2, 54.49 mg of MgSO.sub.4, 43.92 mg of Na.sub.2CO.sub.3 in 1 L water and then enriched with 5% of ATCC 1249 Modified Baar's Medium) was inoculated with a sulfate-reducing bacteria which has a high similarity in 16S rRNA gene sequence with Desulfovibrio alaskensis and Desulfovibrio vietnamensis, at a final bacterial concentrations of 10.sup.7 CFU/mL. The aliquots of this contaminated water were then treated with THPS, sodium nitrate, and THPS/ sodium nitrate combinations at different active concentration levels. After the mixtures were incubated at 35 C. for 2 days, sulfide level in all treatments including non THPS and or nitrate controls were measured using a colorimetric method described by D. Andrew et. al in Standard Methods for the Examination of Water and Wastewater 4500-S2-, with a scaled down sample size (250 l) and reagents (scaled down accordingly) to allow the analysis to be done in 96-well micro-titer plates. Final results were read using a 96-well plate reader (TECAN Sunrise) at wavelength of 580 nm. The treatments that were able to keep the sulfide concentration under 10 ppm was considered effective (failed treatments ended up with a sulfide concentration ranging from 42 to 99 ppm). Table 1 summarizes the efficacy of THPS, nitrate and their combinations, as well as the Synergy Index* of each combination.

[0011] The test results for demonstration of synergy of the combinations are shown in the table below. The table shows the results for each single component and combinations of two components against sulfide production of the microorganisms tested with incubation times; the end-point activity in ppm measured by the level of sulfide control for compound A alone (CA), for component B alone (CB), and the mixture (Ca) and (Cb); the calculated SI value; and the range of synergistic ratios for each combination tested. SI is calculated as follows:

Ca/CA+Cb/CB=Synergy Index (SI)

[0012] Wherein: [0013] Ca=Concentration of biocide A required to achieve a certain level of sulfide control when used in combination with B [0014] CA=Concentration of biocide A required to achieve a certain level of sulfide control when used alone [0015] Cb=Concentration of biocide B required to achieve a certain level of sulfide control when used in combination with A [0016] CB=Concentration of biocide B required to achieve a certain level of sulfide control when used alone
When the sum of Ca/CA and Cb/CB is greater than one, antagonism is indicated. When the sum is equal to one, additivity is indicated, and when less than one, synergism is demonstrated.

TABLE-US-00001 TABLE 1 Sulfide control efficacy of tetrakis(hydroxymethyl) phosphonium sulfate (THPS) and nitrate against anaerobic sulfate-reducing bacteria, and Synergy Index Active ppm concentration Active weight required to control ratio of sulfide below 10 ppm Sulfide Synergy THPS:Nitrate THPS Nitrate (ppm) Index 1:0 12.50 0.0 2.48 32:1 6.25 0.20 7.22 <0.50 16:1 6.25 0.39 3.61 <0.50 4:1 6.25 1.56 7.76 <0.50 2:1 6.25 3.13 8.73 <0.50 1:1 6.25 6.25 2.91 <0.51 1:2 6.25 12.50 4.62 <0.52 1:4 6.25 25.00 6.73 <0.53 1:8 6.25 50.00 7.53 <0.56 1:16 6.25 100.00 3.79 <0.63 0:1 0.0 >800 74.26 * Treatment of THPS alone at 6.25 ppm resulted in 42.15 ppm of sulfide