GB2324727A - Antimicrobial composition containing a silver compound - Google Patents

Abstract

A composition is described which is suitable for use as a toilet block, which composition comprises an antimicrobial composition comprising a silver compound deposited on a support material, preferably a physiologically inert oxidic synthetic particulate support material; and a carrier for the antimicrobial composition, which carrier is adapted to render the composition suitable for use as a toilet block. Preferably, the composition is formed into an in-the-bowl toilet block and contained within a siphonic cage.

Description

Antimicrobial Compositions, their Preparation and Use This invention relates to compositions suitable for use as toilet cleanser blocks, which include an antimicrobial agent for disinfecting water in, for example, the toilet bowl of a water closet. In particular, this invention relates to the incorporation of antimicrobial silver ions into such compositions.

It is known to provide compositions in the form of coherent self-supporting blocks for use in treating the water in toilet bowls. Ordinarily, such blocks are mounted in cage-like containers near the rim of the bowl in a position where, on each occasion the toilet bowl is flushed, the flushing water enters the container and contacts the block to leach out the composition.

It is also known to locate such blocks in the cistern containing the supply of flushing water. In this case, the flushing water entering the toilet bowl already includes the composition.

Usually, the composition in the blocks comprises a simple mixture of a surfactant, a fragrance and a dye to provide a basic cleaning affect and to counter malodours.

It is also desirable to have an antimicrobial agent present in toilet blocks.

It is known to include chlorine-generating agents in the blocks to provide antimicrobial activity, but it is difficult to find fragrances and dyes which are stable in the presence of such chlorine-generating agents. Silver ions are also known to be antimicrobial agents. However, it is well known that, in situations where silver has been used as an antimicrobial, electrochemical methods have been employed to generate the silver ions, such as in swimming pools or coolant systems, which are clearly inapplicable to toilet blocks.

Alternatively, combinations of silver nitrate with a plurality of other inorganic compounds have been proposed. For example, European patent specification no. EP 494 373 discloses a composition for treating swimming pools comprising copper sulphate, silver nitrate, sodium gluconate and zinc chloride or sulphate with water and a complexone such as EDTA. Japanese patent abstract no. JP 87143655 discloses a bath cleaner comprising a granulated soluble glass of silica, soda, boria, alumina and silver nitrate. Other combinations involving silica and silver nitrate are also known, for example, from Japanese patent abstract no. JP 8333210.

However, there are generally concerns about using metal-based biocides in view of the toxicity associated with the metals. It is clearly desirable to be able to maintain a biocidal concentration of the metal ion without exposing the environment to excess. Furthermore, soluble glass-type compositions and the like cannot compensate for rapid changes in microbial populations and may result in ineffective biocidal action or excess silver in the environment. Where silver ions are eluted from silver complexes such as silver borosilicate, the disadvantage is that colour changes occur in products incorporating these, due to sensitivity of the system to light and/or heat. The known systems therefore fail to provide a controlled release of silver ions by a method suitable for application to toilet blocks in an environment such as toilet cisterns or bowls.

Therefore, until now, the primary antimicrobial system which has been employed in toilet blocks has been one which generates chlorine, such as that described in British patent specification no. 2270084.

According to one aspect of the present invention, there is provided a coherent self-supporting body formed of an antimicrobial composition comprising a source of silver ions as antimicrobial agent, the composition being such that silver ions are released from the composition when the body is in contact with water. For example, there is provided a solid in-the-cistern (ITC) or in-the-bowl (ITB) antimicrobial block containing a source of silver ions, the block being such that it provides a controlled-release of silver ions when the composition is in contact with water.

According to another aspect of the present invention, there is provided a composition suitable for use as a toilet block, which composition comprises a) an antimicrobial composition comprising a silver compound deposited on a support material, preferably a physiologically inert oxidic synthetic particulate support material; and b) a carrier for the antimicrobial composition, which carrier is adapted to render the composition suitable for use as a toilet block.

Preferably, the carrier comprises (i) a water-soluble detergent or surfactant; (ii) preferably, a solubility regulator to retard the rate of dissolution of the block; and (iii) optionally, other ingredients conventionally incorporated into toilet blocks, particularly pigments or colourants.

The carrier preferably is in the form of a coherent self-supporting body which incorporates the antimicrobial composition.

Preferably, the antimicrobial composition is selected from those disclosed in European patent specification no. 251 783, the contents of which are incorporated herein by reference in their entirety.

The antimicrobial silver compound is preferably one which has relatively low solubility in aqueous media and in which the silver is present as an ionic species. The form of the compound should thereby be such that release of ionic silver in solution at an effective level for antimicrobial but non-toxic effect is facilitated. Preferably, the source of the silver ions is a silver salt such as a silver halide, for example silver chloride.

In a preferred embodiment, the composition includes a support material for the source of silver ions. The antimicrobial silver compound may be present at a level of from 1 to 75% by weight of the support material, preferably from 10 to 60% by weight. Preferably, the support material is porous so that it can absorb the silver compound and protect it from ambient light. Suitable support materials are physiologically inert oxidic materials, that is, they comprise either an oxide or a hydroxide, or contain a complex oxy-anion species such as phosphate or sulphate. Suitable materials are essentially insoluble and stable in water or aqueous environments and will not form hydrates. By "stable in water or aqueous environments", we mean to distinguish between those compounds which, in contact with water, form a chemically-bound hydrate on the one hand and those which may absorb water to form an associated aqueous species on the other hand, and to indicate the latter.

Synthetic oxidic materials which may be suitable as physiologically inert supports in antimicrobial compositions according to the invention include oxides of titanium, magnesium, aluminium, silicon, cerium, zirconium, hafnium, niobium and tantalum, calcium hydroxyapatite and barium sulphate, in which the oxidic material is stable in water or aqueous environments. For example, in titanium dioxide, which is a preferred material for use in the present invention, the crystalline forms anatase, rutile and brookite are substantially chemically anhydrous, and one or mor' these forms is suitable for use in the present invention. Fully hydrated or r ydratable oxides of titanium are excluded.

The particle size of support materials for use in the invention is preferably less than 25 micrometres, more preferably in the range of from 1 to 15 micrometres. In general, smaller size particles are preferred, including those in the sub-micrometre range, commensurate with achieving the desired antimicrobial effect. The morphology is preferably such that the structure is highly open. The materials may comprise approximately spherical clusters of crystallites having large physical voidage therebetween. Surface areas may extend from 1 or 2 m2/g up to approximately 240 m2/g, preferably in the range of from 5 to 100 m2/g.

On contact with aqueous media, the support material releases silver ions in a controlled way.

In accordance with a particularly preferred embodiment of the present invention, the support ma; ial is a composite comprising titanium dioxide having an average particle size o. about 1 to 15 micrometres, preferably about 2 to 5 micrometres, and having from about 10 to 80%, preferably 20 to 60%, by weight (based on the composite) of silver chloride incorporated therein.

In addition to including the source of silver ions, the compositions according to this invention may comprise one or more surfactants, colourants, binders, fragrances, anti-limescale agents and fillers. Preferably, reducing agents are excluded, otherwise the silver ion will be reduced to relatively ineffective silver metal.

In appropriate formulations, the surfactants may be anionic surfactants, cationic surfactants or non-ionic surfactants. Examples of suitable anionic surfactants include alkali metal salts of alkyl substituted benzene sulphonic acids, alkali metal salts of long chain fatty sulphates, alkali metal ether sulphates derived from alcohols and alkyl phenols, alkali metal sulphosuccinates and alkali metal sarcosinates. Cationic surfactants may be exemplified by quaternary ammonium bromides and chlorides containing a long chain alkyl group, of which benzalkonium chloride is a particular example. Non-ionic surfactants may be of the betaine or imidazoline types. Other suitable surfactants will be known to those skilled in the art.

The rate of dissolution of the composition may be controlled by the addition of optional solubility control agents. Suitable solubility control agents will usually include materials having a solubility which is lower than the readily soluble components (principally surfactants) of the composition. Such solubility control agents may vary in nature from substantially wholly water-insoluble materials to materials having a low solubility in water. Examples of substantially insoluble solubility control agents include paradichlorobenzene, waxes such as beeswax or carnauba wax, petroleum waxes, long chain fatty acids and alcohols, and esters thereof, and fatty alkylamides. Solubility control agents of limited aqueous solubility may also be used, and examples thereof will be known to those skilled in the art. Typically, these can include various non-ionic surfactants. Suitable solubility control agents are those which can withstand the conditions of manufacture (e.g. pressure, temperature) used in processes (such as extrusion processes) ordinarily used to form the bodies of the invention, and are not limited to the above examples.

Suitably, colourants are commercially available colourants such as "Solvent Yellow 98" from Hoechst or "Solvent Blue 70" from BASF. It will be understood, however, that any colourants known to be suitable in the art can be used.

Suitable binders are starch, starch derivatives, cellulose ethers and polyethylene glycolethers.

Examples of fillers are sodium sulphate and silica.

Preferred compositions of the present invention which are suitable for use as ITC or ITB toilet blocks comprise: (a) from 0.1 to 10% w/w of an antimicrobial composition comprising a silver compound deposited on a support material wherein the amount of silver compound is from 1 to 75% w/w of the support material; and (b) from 90 to 99.9% w/w of a carrier for the antimicrobial composition, the carrier being adapted to render the antimicrobial composition suitable for use as a toilet block; all percentages being by weight of the total composition.

Preferably, the compositions of the present invention comprise from about (a) 0.1 to about 10% w/w an antimicrobial composition comprising a silver salt deposited on particulate titanium dioxide; (b) up to about 80% w/w of a detergent or surfactant; (c) up to about 20% w/w of a solubility regulator; (d) up to about 10% w/w of a pigment or colourant; (e) up to about 20% w/w of a fragrance or perfume; (f) up to about 10% w/w of a limescale preventer; (g) up to about 30% w/w of a foam booster or stabiliser; (h) up to about 25% w/w of a binder; and (i) up to 50% wlwofafiller.

More preferably, the compositions of the present invention comprise (a) from about 0.5 to about 5%, especially from about 0.6 to about 2.5%, w/w of the antimicrobial composition; (b) from about 30% to about 70%, especially from about 40% to about 60%, w/w of a detergent; (c) from about 3% to about 15%, especially from about 4% to about 10%, w/w of a solubility regulator; (d) from about 4% to about 7%, especially about 5% to about 6%, w/w of a colourant; (e) from about 4% to about 15%, especially from about 7% to about 10%, w/w of perfume; (f) from about 3% to about 5%, especially about 4%, w/w of a limescale preventer or inhibitor; (g) up to about 5%, especially up to about 3%, w/w of a foam booster or stabiliser; and (h) from about 4% to about 18%, especially from about 6% to about 17%, w/w of binder(s).

The present invention further provides a process for preparing a composition suitable for use as a toilet block, which process comprises bringing into physical admixture (a) an antimicrobial composition comprising a silver compound deposited on a support material, preferably a physiologically inert oxidic synthetic particulate support material; and (b) a carrier for the antimicrobial composition, which carrier is adapted to render the composition suitable for use as a toilet block.

Preferably, the process comprises (a) reacting silver nitrate with an alkali metal chloride in the presence of titanium dioxide particles to form a silver chloride/titanium dioxide composite; (b) drying the composite; (c) mixing the dry, particulate ingredients of the carrier together with the composite; (d) adding any wet or liquid ingredients of the carrier to the mixture produced by step (c) and; optionally (e) forming (by moulding, tabletting andlor extrusion, for example) toilet blocks of from about 25 to 75g, such as 40 to 559, therefrom and; optionally (f) packaging the blocks so formed directly into a water-soluble film and/or into a cage-like container, preferably a siphonic cage.

The composition of the present invention is particularly suitable for disinfecting the toilet bowl of a water closet and, in a particularly preferred embodiment, the body, preferably of block-like form, is located within a cage-like container adapted to be mounted adjacent to the rim of the toilet bowl.

Preferably, the container is of the siphon type which delivers composition to the toilet bowl at the end of the flushing operation. Thus, in contrast to a simple container, the majority of the composition is retained in the toilet bowl rather than being lost down the drain.

A further aspect of the invention accordingly provides a method of disinfecting water in the toilet bowl of a water closet, which method comprises locating the composition in accordance with the first aspect of the invention in the path followed by the flushing water during flushing of the toilet bowl, and flushing the toilet bowl.

If desired, however, the composition of the present invention may be located in the cistern supplying the flushing water. In this case, the body is preferably encased in a soluble coating material for ease of handling.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is an end view of a first type of container, in its closed configuration, for accommodating a body in accordance with the present invention; Figure 2 is a top view of the container of Figure 1 in its open configuration; Figure 3 is a longitudinal cross section through a part of the container of Figure 2 along line Ill-Ill of Figure 2; Figure 4 is a side view of a second type of container for accommodating a body in accordance with the present invention; Figure 5 is a top view of the container of Figure 4; Figures 6a, 6b and 6c are graphs showing the relationship between the number of flushes and the silver ion content (in parts per billion) of the toilet bowl water after each flush when using an antimicrobial body in accordance with the present invention; Figure 7 is a further graph similar to the graphs of Figures 6a, 6b and 6c; Figures 8a, 8b and 8c are graphs illustrating the relationship between viable test organism count and time in flush water when using different antimicrobial bodies in accordance with the present invention; and Figure 9 shows graphs of surviving number of organisms against time in flush water using an antimicrobial body in accordance with the present invention and using a conventional product.

Referring now to Figures 1, 2 and 3, the container is in the form of a cage formed of rigid plastics material. It includes an upper wall 1 pivotally mounted at one edge to lower wall 2 via hinge mechanism 3 to define a chamber. The chamber is for accommodating an antimicrobial block-like body of the present invention. The container includes a flexible hanger portion 4 comprising a first end 5 secured to an upper part of the lower wall 2 and a second end 6 adapted to be hooked over the rim of a toilet bowl (not shown). The hanger 4 includes a tongue 7 terminating in a free end including an abutment 8 adapted to engage with an abutment of a catch 9 provided at the top of the upper wall 1 so as to prevent undesired pivotal movement of upper wall 1 and lower wall 2 about hinge mechanism 3. The second end 6 of the hanger 4 includes a protrusion 10 which can be inserted into catch 9 to release the free end of the tongue 7 when it is desired to open the container by relative pivotal movement of upper and lower walls 1 and 2 about hinge 3 in order to fit a new body according to the invention.

The upper wall 1 includes a plurality of apertures 11 to enable flushing water to pass through the wall and enter into the chamber. The lower wall 2 is not so provided with apertures. The container includes an upstanding tubular portion 12 at one end and an aperture 13 is provided at the lower part of this tubular portion 12 to provide communication between the interior of the tubular portion 12 and the interior of the chamber. The tubular portion 12 also includes an outlet pipe 14 having an upper first end 15 communicating with the tubular member 12 at a location above the aperture 13 and a lower second end 16 terminating externally of the lower wall 2. The upper end of the tubular portion 12 is effectively sealed by a co-operating part 20 provided on the upper wall 1.

Located in the chamber is a pair of spaced walls 17 upstanding from the lower wall 2 and each including, at the end nearest the tubular portion 12, an upstanding post 18 to assist in retaining the block in position.

In use, the hanger portion 4 is bent so as to enable the protrusion 10 to be inserted into catch 9 to release the tongue 7 whereby the upper wall 1 can be pivoted, about hinge mechanism 3, with respect to the lower wall 2 to enable a body 19 in accordance with the present invention to be placed in the chamber so that it rests on the uppermost edges of walls 17. The container is then mounted on the rim of the toilet bowl by means of hanger 4 so that it is in a position where it will be in the water flow when the toilet is flushed. On flushing, water enters into the chamber via the apertures 11 and leaves the chamber via aperture 13, and outlet pipe 14. As a consequence of the flushing water passing through the chamber, silver ions are conveyed from the body 19 to the toilet bowl to disinfect the water in the toilet bowl. More particularly, after flushing has finished, flushing water still present in the chamber siphons out of the chamber via the pipe 14 and falls into the toilet bowl.

Referring now to Figures 4 and 5, there is shown a cage-like container of the non-siphon type. Here, the container comprises side walls 31 and 32 of rigid plastics material joined together at their lower parts by means of a hinge mechanism 33. The side wall 32 includes a tongue 34 which engages in a receptor portion 35 on side wall 31 so that the side walls 31 and 32 are ordinarily held together to define a chamber for a block-like body 40 in accordance with the present invention. The container includes a flexible hanger 36 secured to the side wall 31 at one end and having a second end 37 to enable the container to be hung on the rim of a toilet bowl. As in the case of the embodiment of Figures 2 to 4, the end 37 may include a protrusion (not shown) to enable the tongue 34 to be released from the receptor portion 35 when it is desired to open the chamber to insert a fresh anti-microbial body.

The side walls 31 and 32 are provided with apertures 38 and the lower part of side wall 32 is provided with apertures 39.

In use, the container is suspended on rim of the toilet bowl by the hanger 36 in a position where it will be contacted by the water during flushing. During flushing the water enters into the chamber via apertures 38, passes over the body 40 and leaches silver ions therefrom, and then leaves the chamber via bottom apertures 39 to fall into the toilet bowl wherein the silver ions disinfect the toilet bowl water and adjacent surfaces of the bowl.

The following Examples illustrate the invention.

EXAMPLE 1 A free-flowing titanium dioxide/silver chloride composite powder was prepared by reacting silver nitrate with sodium chloride in the presence of titanium dioxide particles having an average size of from about 2 to 3 micrometres so that, after drying, the composite contained 20% by weight silver chloride and 80% by weight titanium dioxide. 2.5% w/w of the composite was then admixed thoroughly with the following ingredients: Ingredient % w/w composition Silica 8.7 Sodium dodecylbenzene sulphonate 34.6 Sodium C14-C16 olefin sulphonate 28.9 Trisodium citrate 4.3 Sodium sulphate (heavy) 4.4 Corn starch 8.6 8.0% w/w of a perfume was then poured into a hole scooped in the mixture, and the mixture was scooped over the perfume and agitated with a spatula to ensure thorough mixing. The resultant mixture was transferred to a Haake Rheocord EU-3V mixer wherein it was mixed for 10 minutes at a speed of 30 rpm, noting the torque reading each minute in order to ensure consistency in mixing the blocks. After 10 minutes, the resultant paste was transferred quantitatively to a balance and divided into 40 gram lots. Each lot was then transferred to a mould and subjected to a pressure of two atmospheres to mould the paste into coherent self-supporting blocks. Each block was then sealed in a bag of plastics material until ready for use.

The efficacy of the blocks for disinfecting toilet bowl water was then ascertained by carrying out tests run in parallel on two different test rigs, each including an automatic flushing toilet. Each block was located in a cage-like container and mounted at the toilet rim. The flush cycle was set at 30 flushes every 24 hours with a uniform time interval between flushes. Generally, about 0.1 gram of the composition was leached away at each flush. After each flush, the degree of silver dosing achieved was determined by collecting a sample of the water from the toilet bowl, fixing the silver present in the water with 1 % nitric acid, and then analyzing it by lCP-MS (Inductively Coupled Plasma Mass Spectrometry).

The results obtained are shown in the graphs of Figures 6a, 6b and 6c of the accompanying drawings. In each Figure, four graphs are depicted. Graphs A and B show the results obtained when siphon containers of the type shown in Figures 1, 2 and 3 were used on the two different test rigs, and graphs C and D show the results obtained when using non-siphon containers of the type shown in Figures 4 and 5 on the two different test rigs. As can be seen from the graphs, an amount of silver ion effective to provide antimicrobial properties was present in the toilet bowl water after each flush. Generally, however, up until about 320 flushes had been performed, the silver ion concentration in the water was greater when the siphon container was used.

EXAMPLE 2 Example 1 was repeated except that in a first experiment the block contained 0.6% w/w of the composite and in a second experiment the block contained 1.25% w/w of the composite. The results obtained in each case are shown in the graph of Figure 7 of the accompanying drawings. Again, an amount of silver ion effective to provide antimicrobial properties was present in the toilet bowl after a large number of flushes.

EXAMPLE 3 Lavatory blocks were prepared as described in Example 1 and included respectively 0.625% wlw, 1.25 w/w and 2.5% w/w of the composite. These blocks were mounted in a flushing toilet subjected to normal use and a sample of flush water was collected after the number of flushes indicated in Table 1.

Table 1 Composite Content (%w/w) No. of Flushes 0.625 75 1.25 65 2.5 70 Samples of the collected flush water were inoculated with, respectively, approximately 1,000,000 cfu/ml E.coli and 1000 cfu/ml E.coli. Total viable counts were then measured at various time intervals. The results are presented in Figures 8a (0.625% composite), 8b (1.25% composite) and 8c (2.5% composite), from which it can be seen that the lavatory blocks were effective against E.coli at all tested composite contents.

EXAMPLE 4 Lavatory blocks prepared as described in Example 1 and including 1.25% w/w of the composite were tested for antimicrobial efficacy against Pseudomonas aeruginosa, Enterococcus hirae and Eschenchia coli, using the method described in Example 3. Samples of flush water after 50 flushes were taken out, and 1 hour later, were inoculated respectively with approximately 1,000,000 cfu/ml of each of the above test organisms. As a comparison, tests were also performed using a lavatory block containing 15-30% of a chlorine-based bleaching agent (sodium dichloroisocyanurate (DCCNa)).

The results are presented in Figure 9, from which it is apparent that the lavatory blocks of the present invention were significantly more effective against the test organisms than the DCCNa-containing lavatory block.

EXAMPLE 5 To determine prolonged antimicrobial activity, lavatory blocks were prepared as described in Example 1 with 1.25% w/w of the composite and tested against Escherichia coli and Pseudomonas aeruginosa. As a comparison, tests were also performed using a lavatory block containing 15-30% sodium dichloroisocyanurate (DCCNa).

Each block was located in a siphonic cage and mounted on the toilet rim.

After 60 flushes, water samples were taken from the lavatory bowl and also on one occasion from the cistern as a control.

The water samples were split into two, and one sample was inoculated with approximately 1.0x103 cfu/ml E. coli and the other sample with a similar inoculum of Ps. aeruginosa. Total viable counts (TVC) of the inoculated samples were then measured at various times over a 24 hour period. The organism inoculum was prepared by washing 3 times in distilled water by centrifuging at 3000 ppm in a refrigerated centrifuge. The finai pellet of organisms was suspended in distilled water to minimise extraneous organic soiling of the samples.

After 24 hours, the water samples were reinoculated with the relevant organisms and again had TVC carried out over a further 24 hour period.

Reinoculation and TVC was repeated a further three times, giving a total of five inoculation of microorganisms into each flush water sample. The TVC indicated the numbers of residual organisms and was compared to the baseline count, and the microbiocidal effect was then determined.

The results obtained are shown in Table 2.

Table 2 Inoculation E. coli Ps. aeruginosa Eradication time Eradication time in hours in hours 1 sot 1.25% w/w composite 6 8 DCCNa 1.0x102* 6 2nd 1.25% wlw composite 24 24 DCCNa NR NR 3rd 1.25% w/w composite 24 24 DCCNa NR NR 4th 1.25% w/w composite 24 24 DCCNa NR NR 5th 1.25% w/w composite 1 .0x1 02* 1 .0x1 0* DCCNa NR NR * = reduction factor in 24 hours where eradication is not achieved.

NR = no reduction in count compared to baseline count.

The results show that, with the lavatory blocks of the present invention, there is evidence of prolonged antimicrobial activity which is able to resist repeated challenge over a four day period of E. coli and Ps. aeruginosa. In contrast, the DCCNa-containing block only showed comparable antimicrobial activity for one day with a single inoculation of the challenge organism. The results demonstrate that, if lavatory blocks of the present invention are used, the ability of the toilet flush water to resist repeat challenge with typicai water-borne and intestinal/food poisoning microorganisms, between flushes, is in the order of 4 to 5 times greater than if a comparative DCCNa-containing block is used.

Claims (11)

1. A coherent self-supporting body formed of an antimicrobial composition comprising a source of silver ions as antimicrobial agent, the composition being such that silver ions are released from the composition when the body is in contact with water.

2. A composition suitable for use as a toilet block, which composition comprises (a) an antimicrobial composition comprising a silver compound deposited on a support material, preferably a physiologically inert oxidic synthetic particulate support material; and (b) a carrier for the antimicrobial composition, which carrier is adapted to render the composition suitable for use as a toilet block.

3. A composition according to claim 1 or claim 2, wherein the body or carrier comprises (i) a water-soluble detergent or surfactant; and (ii) optionally, a solubility regulator to retard the rate of dissolution.

4. A composition according to any preceding claim, wherein the source of the silver ions is a silver salt such as a silver halide.

5. A composition according to any preceding claim, wherein the source of the silver ions is silver chloride.

6. A composition according to any preceding claim, wherein the composition includes a support material for the source of silver ions, which support material comprises either an oxide or a hydroxide, or contains a complex oxy-anion species such as phosphate or sulphate.

7. A composition according to any preceding claim, wherein the support material is a composite comprising titanium dioxide having an average particle size of about 1 to 15 micrometres and having from about 10 to 80 by weight (based on the composite) of silver chloride incorporated therein.

8. A composition according to any preceding claim, comprising (a) from about 0.1 to about 10% w/w of an antimicrobial composition comprising a silver salt deposited on particulate titanium dioxide; (b) up to about 80% wlw of a detergent or surfactant; (c) up to about 20% w/w of a solubility regulator; (d) up to about 10% w/w of a pigment or colourant; (e) up to about 20% w/w of a fragrance or perfume; (f) up to about 10% w/w of a limescale preventer; (g) up to about 30% w/w of a foam booster or stabiliser; (h) up to about 20% w/w of a binder; and (i) up to about 50% w/w of a filler.

9. An antimicrobial toilet block, preferably an ITB or ITC block, comprising an antimicrobially effective amount of a source of silver ions, whereby the silver ions are control-released from the block when the block is in contact with water.

10. A process for preparing a composition suitable for use as a toilet block, which process comprises mixing (a) an antimicrobial composition comprising a silver compound deposited on a support material, preferably a physiologically inert oxidic synthetic particulate support material; and (b) a carrier for the antimicrobial composition, which carrier is adapted to render the composition suitable for use as a toilet block.

11. A process according to claim 10, comprising (a) reacting silver nitrate with an alkali metal chloride in the presence of titanium dioxide particles to form a silver chloride/titanium dioxide composite; (b) drying the composite; (c) mixing the dry, particulate ingredients of the carrier together with the composite; (d) adding any wet or liquid ingredients of the carrier to the mixture produced by step (c) and; optionally (e) forming toilet blocks of from about 25 to 759 therefrom and; optionally (f) packaging the blocks so formed directly into a water-soluble film andlor into a cage-like container.