US5017295A

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United States Patent {19] {11] Patent Number: 5,017,295
Antelman . [45] Date of Patent: May 21, 1991
{54] DIVALENT SILVER BACTERICIDE FOR Primary Examiner—Stanley Silverman
WATER TREATMENT Assistant Examiner—Neil M. McCarthy
[75] Inventor: Marvin S. Antelman, Rehovot, Israel Attorney, Agent, or Firm—Salter & Michaelson
{73} Assignee: N, Jonas & Co., Inc., Bensalem, Pa. 157] ABSTRACT
. A method or methods of controlling the growth of
Bt) Appl. Not 517,169 bacteria in the water of swimming pools and/or indus-
[22] Filed: May 1, 1990 trial water supplies by adding to the water a specified
[51] Int. CLS C02F 1/50 concentration of a stable divalent silver compound. The
[52] US. CL 210/764; 422/19, invention has the advantage over chlorination in that it
; 424/618; 514/495 is odorless and non-volatile. It furthermore is superior
[58] Field of Search ......0...0..0... 210/764, 169; 422/28, to monovalent silver compounds as these compounds
422/19; 424/618; 514/495 do not decompose in the presence of light and resist
. precipitation by halides and form divalent soluble com-
66] References Cited plexes which in the monovalent state are invariably
U.S. PATENT DOCUMENTS insoluble solids.
4,055,655 10/1977 Maurer et al. 514/495
4,092,245 5/1978 Franks et al. .. 424/618 5 Claims, No Drawings

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5,017,295

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DIVALENT SILVER BACTERICIDE FOR WATER
TREATMENT

BACKGROUND OF THE INVENTION

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Industrial cooling water is prone to bacterial contam- _

ination as it may stand for long periods of time and
breed bacteria. On the other hand, swimming pool
water is constantly recirculated and fresh water is
added to maintain a constant volume, and is filtered to
remove particulate matter. Nevertheless, said water is
constantly exposed to infection by microbes.

The primary disinfectant for swimming pool water is
. chlorine which causes eye irritation and breathing diffi-
culties in certain sensitive individuals. Chlorine and its
reaction products with water are volatile and dissipate.
Chlorine also is prone to form carcinogenic chloramines
in underchlorinated pools and will also form haloforms
which are harmful to the ecosystem. While all the afore-
mentioned problems relating to people utilizing swim-
ming pools do not apply to industrial cooling water,
increased public awareness has precluded the use of
such bactericides as mercury-based compounds, which
harm the biosphere. To such water and all the other
problems pertaining to chlorine is the instant invention
directed.

The metal silver in its monovalent state has been
suggested as a bactericide for these applications. It,
unlike chlorine, does not dissipate and is more compati-
ble with the environment and does not cause the ad-
verse reactions in humans known to chlorine. However,
large concentrations of this precious metal are required.
It also has a tendency to precipitate, stain and decom-
pose in the presence of light.

OBJECTS OF THE INVENTION

An important object of this invention is to provide a
silver-based bactericidic agent for industrial cooling
and swimming pool water that is more stable than
monovalent silver.

Still another object of this invention is to provide for
silver in a more potent form as a bactericide so that it
will kill at tower levels of silver then has heretofore
been known to those skilled in the art of utilizing such
substances.

Other objects, features and advantages of the inven-
tion shall become apparent as the description thereof
proceeds when considered in connection with the ac-
companying specific examples.

SUMMARY OF THE INVENTION

This invention relates to methods for keeping the
water in swimming pools and in industrial cooling in-
stallations free from bacteria. Said methods relate to
bactericidic agents based on divalent silver compounds
which are: used: as. disinfectants. More particularly, this
invention concerns those divalent silver compounds
which form stable complexes.

Divalent silver complexes are prepared by reacting
silver(I] oxide with various acids that form stable silver
complexes. Said complexes are then evaluated as to
their efficacy in killing streptococcus faecalis which is
the accepted protocol for swimming pool and cooling
water disinfectants.

When the stable silver (II) complexes were evaluated
in this manner, it was found that there were 100% kills

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of bacteria within 5 minutes at concentrations of silver
as low as 2 parts per million.

It was also found that at these effective concentra-
tions and higher, there was no chloride precipitation
from water containing 0.1 gram of sodium chloride per
liter which would precipitate soluble silver at the same
concentrations in the monovalent state.

When stable Ag(IT) compounds were exposed to light
for long periods of time, there was either very slight
evidence of decomposition or none at all in contradis-
tinction to those monovalent solutions which decom-
posed.

Stable divalent silver compounds which were effec-
tive have been defined in the literature. For example, G.
A. Rechnitz and S. B. Zamochnick have studied the
behavior of Ag(II) in phosphoric acid (Talanta, 1965,
Vol. 12, 479-83) and found the complexes to be stable.

I have found that Ag(II) phosphates and fluoborates
are particularly excellent disinfectants and are ex-
tremely stable, whereas Ag(II) ammonium sulfate and
methanesulfonate are unstable and not good disinfec-
tants.

DESCRIPTION OF THE PREFERRED
EMBODIMENTS

As illustrative of the compositions of this invention in
their preferred embodiments is the following:

EXAMPLE 1

Silver (II) oxide was prepared by modifying the pro-
cedure described by Hammer and Kleinberg in Jno-
roanic Syntheses (IV, 12). A stock solution was prepared
by dissolving 24.0 grams of sodium hydroxide in 500 ml.
of distilled water which had previously been made to
said volume after dissolving 24.0 grams of potassium
peroxydisulfate. Into 20 ml. vials were weighed silver
nitrate containing 1.0 gram of silver. Now 50 ml. of the
aforementioned stock solution were heated in a 100 ml.
beaker, and the contents of one of the vials was added to
the solution after it had reached the temperature of 85°
C. The beaker was then heated to 90° C. for 15 minutes.
The subsequent silver (II) oxide which formed as a deep
black precipitate was washed and decanted 4 times with
distilled water. It was then dissolved in 25 ml. of 85%
reagent grade phosphoric acid and unlike the monova-
lent phosphate was soluble in water. 100 ml. of this
solution was added to a liter of distilled water to give a
final concentration of silver that was 4.0 parts per mil-
lion. This in turn was submitted to a bactericidic pre-
screening following “good laboratory practice regula-
tions” as set forth in Federal regulations (FIFRA and
ffdca/40 CFR 160, May 2, 1984). The protocol con-
sisted of exposures to streptococcus faecalis using
AOAC (15th) 1990:965:13 at two exposure times, 5 and
10 minutes. The results were 100% kills of bacteria. The
tests were repeated using the same solution at one-half
the silver concentration. The results were the same at
2.0 parts per million silver.

Both silver (II) phosphate solutions at 2.0 and 4.0
parts per million, respectively, were subjected to mixing
with 0. 100 grams of sodium chloride dissolved in a liter
of water. There was no precipitation of chloride at all.

Both silver (II) solutions were exposed for 45 days to
the Mediterranean sun in the State of Israel at Rehovot,
for a period of 45 days during the months of January
and February. There was only a slight darkening at the
bottom of the vial of 4.0 ppm solution, and absolutely
none in the 2.0 ppm solution. Silver nitrate solutions at

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5,017,295

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the same concentrations of silver darkened in less than
48 hours, under the same conditions.

EXAMPLE 2

Silver (II) oxide was prepared in the manner de- 5
scribed in Example 1. Silver oxide (AgO) containing 1
gram of silver was dissolved in 10 cc of 48% fluoboric
acid. The resulting colorless solution was tested accord-
ing to the aforementioned protocol involving strepto-
coccus faecalis where the silver (II) concentration of 10
the fluoborate was 5.0 ppm. 100% kills resulted after 5
and 10 minutes. This was then compared with a prepa-
ration of monovalent silver fluoborate obtained from
the reaction of silver (I) oxide with fluoboric acid. The
Ag(I) fluoborate at a concentration of 62.5 ppm did not
prevent the bacteria from reproducing. Exposure of the
resulting Ag(II) solution to sunlight according to the
procedure described in Example 1 did not yield any
evidence of decomposition whatsoever.

The divalent silver phosphate solution of Example 1
and the divalent silver fluoborate solution of Example 2
tepresent classes of compounds known in the art as
inorganic ligands, i.e., the silver atoms are attached to
inorganic ligands.

As this invention may be embodied in several forms
without departing from the spirit or essential character-
istics thereof, the present embodiment is therefore illus-

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trative and not restrictive, since the scope of the inven-
tion is defined by the appended claims rather than by
the description preceding them, and all changes that fall
within the metes and bounds of the claims or that form
their functional as well as conjointly cooperative equiv-
alents, are therefore intended to be embraced by these
claims.

What is claimed is:

1. A method for controlling the growth of bacteria in
the water of swimming pools and industrial cooling
water which comprises adding to the water a stable
divalent silver complex compounds, said silver complex
compound comprising divalent silver attached to an
inorganic ligand.

2. A method as claimed in claim 1 wherein the diva-
lent silver complex compound is used in a amount to
provide a silver concentration from 0.5 to 15 parts per
million.

3. The method of claim 1 wherein said inorganic
ligand is fluoborate.

4. The method of claim 1 wherein said inorganic
ligand is phosphate.

5. The method of claim 1 wherein the divalent silver
complex compound is light stable so as not to discolor
or leave black silver films on the inner surface of vessels

containing the water to be treated.
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