GB2318349A - Biocidal composition for wet environment - Google Patents

Abstract

A biocidal composition which, when associated with a surface is capable of controlling the accumulation of organisms/organic matter in an aqueous/humid environment at or near the surface, comprises a transition metal ion and a chelate binding to the metal ion, the composition being such that, in the presence of an oxygen source and preferably a reducing agent, it is capable of continuously generating a reactive oxygen species (eg a peroxide, superoxide or hydroxyl radical) in biocidal amounts, the metal ion being so firmly associated with the chelate that it does not dissociate into the aqueous environment. The surface may be eg a ship's hull, a water pipe, a rope, a filter or a medical bandage.

Description

METHOD OF CONTROLLING THE ACCUMULATION AND/OR THE VIABILITY OF ORGANISMS ON OR IN PROXIMITY TO AN IMMERSED OR WET SURFACE FIELD OF INVENTION This invention relates to preventing the fouling of submerged surfaces by organic molecules and biological organisms and to impairing the viability of organisms present in aqueous media in proximity to surfaces by associating with said surfaces a chemical system which is capable of continuously generating or releasing reactive oxygen species.

TECHNICAL BACKGROUND AND PRIOR ART The fouling of ship's hulls and other surfaces by micro-organisms and macro-organisms is a well known problem. Such fouling occurs through a multistage process (Wahl, 1989), of which the four most important stages are: 1. Deposition of a layer of organic molecules on the ship's hull or surface; 2. Settling and growth of ma,rine.micro-organisms on the organic layer; 3. Settling of macro-organism larvae on the micro-organism layer; 4. Growth of larvae into sessile macro-organisms (e.g barnacles) which cause drag.

On such a model, fouling can in principle be prevented by interfering with any one of these stages A wide variety of compounds have been proposed and used to prevent such fouling, most notably tin and copper containing paints which are applied to the ship's hull. To date all com mercially viable compounds are based on long lasting poisonous or toxic compounds which have detrimental environmental effects.

A wide variety of compounds and approaches have been proposed which, according to their proponents, do not have such detrimental effects. These include non-stick coatings of the Teflon type, antibiotics and other approaches. In WO 92/07037 is disclosed an anti-fouling composition based on the activity of copper ions which has a reduced toxicity. This composition comprises an ion exchange resin capable of selectively binding copper such as copper ions present in aquatic environments.

Most compounds and approaches that can be applied to preventing the fouling of ships can, subject to safety concerns, also be applied to prevent the fouling of other surfaces, most obviously other submerged marine structures, but also other non-marine water transport or containment systems. One particularly important application is in the water inlet and outlet systems of power stations, which frequently require utilisation of water in a cooling or power generation capacity and which, in particular due to the heating of the water that occurs, can suffer major problems of fouling and hence blocking of intakes and outlets.

Surfaces do not need to be submerged constantly, or indeed to be submerged at all to face a problem of fouling. Given a sufficiently humid or wet environment, micro-organisms will colonise many forms of surfaces such as roofs, wooden structures, plastics, the walls of buildings, clothing or other fabrics, medical devices, packaging materials, bandages and dressings, skin and even industrial machinery such as oil drilling equipment. In many such cases the presence of microorganisms in layers presents a significant aesthetic problem.

In other cases the micro-organisms can, either directly or indirectly (by facilitating the settling of other organisms) cause a medical or structural problem to develop.

Biocidally active compounds (biocides) are also used to reduce the presence, or prevent the build up, of undesired micro-organisms in water bodies or aquatic environments themselves. They can be either periodically applied directly to the body of water, or alternatively be introduced into the environment via diffusion from a surface which is in contact with the water body. The biocide is being used to partially or fully sterilise or disinfect the water body. Applications of such systems most obviously include the sterilisation or disinfection of drinking water and the treatment of household effluent, sewage or industrial waste both in holding tanks and in the sewer system itself. They are also widely used in building air conditioning and ventilation systems (where the build up of such organisms as Legionella spp can be a health problem for the occupants). They can further be used to prevent the contamination of aquatic environments such as processing tanks, filters and as a way of controlling residual or subsequent contamination of foodstuffs and drinks.

Active or reactive oxygen species (ROS) are highly reactive at normal temperatures. In particular they react with various component molecules of living organisms. This makes ROS potentially useful bactericidal and sterilising agents.

The use of active oxygen species as antifouling or disinfecting agents in association with marine and other aquatic environments and wet surfaces in general is known e.g. from WO 93/02973 and JP 89-117227. JP 83-28345 discloses the use of a peroxide of a group IIa metal in a marine anti-foulant for application to a ship's hull to prevent adhesion of marine organisms.

Whereas known methods of controlling the association of submersed, aqueous, wet or intermittently wet surfaces with micro-organisms or macro-organisms, or the viability of such organisms in environments being in the proximity to such surfaces, are either based on the use of toxic compounds or on the use of active oxygen species which is continuously fed to the surfaces or the environments, the present method is based on the use of an in-situ chemical system comprising a redox active transition metal ion firmly associated with a chelating agent, the system being capable of continuously generating reactive oxygen species in biocidally active amounts.

SUMMARY OF THE INVENTION Accordingly, the invention relates in a first aspect to a method of controlling in an aqueous, humid or intermittently humid environment the accumulation of organisms or organic matter on a surface, the method comprising associating with said surface a chemical system which in the presence of an oxygen source and a reducing agent is capable of continuously generating reactive oxygen species in biocidally active amounts, the system comprising (i) a redox active transition metal ion and (ii) a chelating compound which binds to the metal ion, the metal ion being so firmly associated with the chelating agent that it essentially does not dissociate into the aqueous environment.

In another aspect the invention pertains to a method of impairing or controlling the via-bility of organisms in an aqueous, humid or intermittently humid environment, where that environment is in proximity to a surface, said method comprising associating to said surface a chemical system which in the presence of an oxygen source and a reducing agent is capable of continuously generating reactive oxygen species in biocidally active amounts, the system comprising (i) a redox active transition metal ion and (ii) a chelating compound which binds to the metal ion, the metal ion being so firmly associated with the chelating agent that it essentially does not dissociate into the aqueous environment.

The invention provides in further aspects (1) a composition which when associated with a surface is capable of controlling the accumulation of organisms and organic matter on said surface when placed in an aqueous, humid or intermittently humid environment, the composition comprising a chemical system which in the presence of an oxygen source and a reducing agent is capable of continuously generating reactive oxygen species in biocidally active amounts, the system comprising (i) a redox active transition metal ion and (ii) a compound which binds to the metal ion, the metal ion being so firmly associated with the chelating agent that it essentially does not dissociate into the aqueous environment, and (2) a composition which when associated with a surface is capable of impairing the viability of organisms in an aqueous, humid or intermittently humid environment, the composition comprising a chemical system which in the presence of an oxygen source and a reducing agent is capable of continuously generating reactive oxygen species in biocidally active amounts, the system comprising (i) a redox active transition metal ion and (ii) a chelating compound which binds to the metal ion, the metal ion being so firmly associated with the chelating agent that it essentially does not dissociate into the aqueous environment.

DETAILED DISCLOSURE OF THE INVENTION The present invention relates, as it is mentioned above, in one aspect to methods of preventing the settling and growth of micro-organisms and/or the deposition of organic material on submerged, humid or intermittently humid surfaces, such methods being characterised by the continuous production or release of active oxygen species (e.g. superoxides, peroxides and hydroxyl radicals) in biocidally effective amounts at or near the surface being protected. The present invention also relates to impairing the viability of organisms in aqueous media in proximity to surfaces.

In the present context, the expression "associating with a surface" indicates that the ROS generating system is either incorporated into a coating or surface layer covering the surface to be protected from fouling or that the system is bound or linked to the surface itself. Thus, as a typical example, the system can be incorporated into an anti-fouling paint composition.

It will be understood that this above expression also refers to the situation where the object of the method according to the invention is not only to prevent fouling of the surface itself but also to impair the viability of organisms in an aqueous or wet environment in the proximity to the surface.

As used herein, the expression "in the proximity to the surface" is used to describe the distance from the surface over which the concentration of the generated reactive oxygen species is sufficiently high to impair the viability of undesired organisms present in the environment. It is contemplated that this distance, depending on the particular system applied, will be in the range of 0-100 cm such as in the range of 0-50 cm, including the range of 0-25 cm such as in the range of 0-10 cm.

The above expression "impairing the viability" refers to an effect whereby a substantial proportion of living organisms including micro-organisms such as bacteria that are present in the aqueous or wet environment are killed or inhibited with respect to growth or other manifestations of viability.

The effect referred to is that of a disinfection or biocidal effect.

In accordance with the invention, the in-situ reactive oxygen species generating system comprises at least two elements, i.e. (i) a redox active transition metal ion and (ii) a chelating compound which is capable of binding to the metal ion. However, for the system to be effective it is required that an oxygen source and a reducing agent is present. In accordance with the invention, suitable oxygen sources may be present in the aqueous or wet environment as free oxygen or as oxygen bound to organic or inorganic moieties. Alternative, an oxygen source may be incorporated into the chemical system according to the invention.

Suitable reducing agents will normally be abundantly present in the aqueous or wet environment, but such agents may also, if required, be added to the system.

Active oxygen species have a short half-life compared to the desired life-time of an anti-fouling system or coating. It is therefore desirable to generate a constant or continuous flow of active oxygen species in-situ at or near the surface of the coating. In accordance with the invention, a constant production of reactive oxygen species will typically be initiated by the well known metal ion catalyzed electron transfer to molecular oxygen.

The fixation or binding of the metal ions to the surface will typically be made by complexing the ions to metal chelators to form chelates followed by binding or anchoring these chelates to the surface. This binding or anchoring of chelates is advantageously carried out via substituents which are linked to the chelating agents or chelators. Such anchoring can either be made during the polymerisation process leading to the coating or surface layer comprising the system or by attachment independent of the polymerisation process.

Chemical generation of reactive oxygen species is a stepwise electron transfer from the metal ion to molecular oxygen.

Subsequent proton transfer forms hydrogen peroxide and/or hydroxyl radicals. The general reaction scheme is shown in Scheme 1 below: Scheme 1.

Super- Hydrogen- Hydroxyl- Water oxide peroxide radical All three oxygen species are highly oxidative and have higher oxidation potentials than e.g. bromine and chlorine and as such they can be regarded as potent disinfectants. This electron transfer sequence can be catalyzed by different metal ions including: Fe, Cu, Zn, Cd, Pb, Co and Ru ions.

The redox mechanism can be exemplified by the Fe(II)/Fe(III) system. Fe(II) is capable of transferring an electron to molecular oxygen giving rise to superoxide, with itself being oxidised to Fe(III). Fe(III) is easy to reduce and can be reduced by most reducing agents. Thus it has been shown that the reduction potential of EDTAFe(III) to EDTAFe(II) is very low (EO= 0.117 V). This means that even very weak reducing agents such as the widely found agent hydrogen sulphide and 3-mercaptopropionic acid and DTE are capable of reducing EDTAFe(III). Other reducing agents such as NADH and ascorbate are also able to carry out this reaction. Such compounds are found as components in heterogeneous biological aqueous en vironments. It has been shown that chelation of Fe(III) (e.g. by NTA, EDTA) makes the reduction of Fe(III) even easier. Superoxide and hydrogen peroxide may also be reduced and thus 3 electrons are required to form hydroxyl radicals which are the end product (Scheme 2).

Scheme 2.

Super- Hydrogen- Hydroxyl- Water oxide peroxide radical

Mn > Mn I Mn o -----) M+1 Red. Agent Red. Agent Mtn Red. Agent In accordance with the invention, the key issue in the above chemical system is its continuous or cyclic nature. Thus, the presence of reducing agents will result in a steady flow of reactive oxygen species.

A range of different chelating agents or chelators can be used in the present invention. Without being bound by examples these include the group of chelators listed below which are well known to a person skilled in the art.

EDTA : Ethylenediamine-tetraacetic acid or (ethylenedinitril) tetraacetic Acid ECTA: [N- (2-Ethylnitrilodiacetic Acid) -1,2-Cyclohexylene dinitrilo] Triacetic Acid EHPG: N,N' -Ethylene bis [2-(2-hydroxy-5-chlorophenyl) Glycine] HOEDTA: N- (Caroxymethyl) -N' - (2-hydroxyethyl) -N,N' Ethylene Diglycine CHCEDG: N- Carboxymethyl)- -N' -2-Hydroxycyclohexyl-N,N' - Ethylene-Diglycine CH3EHPG: N,N' Ethylene bis [2-(2-Hydroxy-5-methylphenyl) Glycine] CDTA: (1,2-Cyclohexylenedinitrilo) Tetraacetic Acid EHCHG: N,N, Ethylene bis (N-2-Hydroxycyclohexylglycine) NTA: Nitrilotriacetic Acid HEIDA: [(2-Hydroxyethyl) Imino] Diacetic Acid DTPA: [(Carboxymethyl) Imino bis (ethylenenitrilo)] Tetraacetic Acid EHPG: N,N' Ethylene bis [2-(o-Hydroxyphenyl) Glycine] DHEG: N,N'-bis (2-hydroxyethyl) Glycine The usefulness of the above-mentioned chelating compounds can be further increased by using either a combination of compounds or by derivatising the compounds. Derivatisation serves at least three important purposes: (i) to anchor the chelate to the surface, (ii) to enhance affinity/specificity of the ion chelation and (iii) to modulate surface polarity.

With respect to the above purpose (i), the fixation of the chelate to the surface is essential to the in-situ/surface production of reactive oxygen species. One way to achieve this is by introducing substituents with long lipophilic chains in the chelator hence facilitating binding or anchoring of the chelator to the surface during the polymerisation process. One example of a suitable substituent is a substituent comprising an anthraquinone group. The substitution can be done via acid derivatives or by direct substitution on the carbon skeleton of the chelator. These chains may (or may not) have functional groups which can be functional groups participating in the hardening of the coating comprising the system according to the invention. Another way of fixating the chelating agent to the surface is by attaching the chelate to the surface after polymerisation has occurred either by chemical and/or physical activation of the surface followed by attachment of the chelate. Still another way is by direct attachment of the chelate to the unmodified surface.

In sea water the ion concentration of metals present herein is subject to considerable variations. The ions found in the highest concentration are Mg2+ and Ca2+. These metal ions are not active in the catalytic production of reactive oxygen species but they will bind to the anionic chelators described above although ions of transition metals such as Fe, Co, Ni, Cu or Zn which are redox active will bind preferentially.

However, this "contamination" by Mg and Ca which is mainly caused by electrostatic interaction can be avoided by a derivatisation with a non-charged or neutral substituent such as e.g. hydroxylamine. It has been shown that non-charged hydroxylamine derivatives of e.g. EDTA and NTA chelate transition metal ions specifically and in fact co-ordinate e.g.

Fe(II) even more strongly (Hirotsu et al.,1985) (Scheme 3).

Scheme 3.

Another effect of having neutral chelates on the surface is that they enhance the lipophilicity of the surface. This feature has been shown to be an important property in anti fouling (Wahl, 1989).

In conclusion substituents on the basic chelator structures can be used for the following purposes: 1. Fixating the chelates to the surface.

2. Increasing the affinity of redox active transition metals to the chelator and the discrimination between redox inac tive/redox active metals.

3. Decreasing the polarity of the surface.

The terms R, R' as used in the above Schemes and the below Scheme 4 designate different substituents which terms in this connection are broadly defined and comprise most organic structures with or without functional groups. Most preferred are structures which comprise alkyl, alkenyl, alkynyl, cyclo alkyl or aryl.

A number of different compounds of variable complexity (and consequently varied activity) can be envisaged as it is illustrated in Scheme 4.

Scheme 4.

The method according to the invention is useful for controlling fouling of any submersed or wet surface or for impairing the viability of organisms on or in proximity to such surfaces, and the use of the method is contemplated for a variety of surfaces including as examples a ship's hull, a water storage reservoir, a waste water reservoir, the inner surface of a water pipe or tubing for transportation of liquid media, a liquor container, a fish net, an anchor, a rope, a roof, a fence, a boat, a submarine, a water inlet or outlet of a power station and other industrial plants, an aqueduct, a canalised waterway, a submerged marine structure, an industrial processing tank, an air conditioning system, a filter, a medical bandage or plaster, a packaging foil, a film, a plastic, paper for storage of foods and fluids, a medical device, a pharmaceutical, a household or industrial appliance and a book.

In interesting aspects of the invention there is also provided herein compositions which are useful in the above methods and which accordingly have the composition and features as described above. Although it is preferred that the composition does not include environmentally detrimental compounds, it is contemplated that the compositions may, for certain uses, advantageously comprise a biocidally active compound.

In accordance with the invention, the composition may be a paint or coating composition such as an anti-fouling paint for surfaces submersed in sea water, including a paint for ships or other vessels including an oil drilling platform.

EXAMPLES Materials and Methods.

The presence of reactive oxygen species (ROS) was analyzed indirectly by following the bleaching over time of Murexide (Mu) as described by Torreilles et al. (1989). Metal ions were immobilised on a Chelix resin (purchased from BIO-RADX

which serves as the surface in the experiments. Murexide was purchased from Aldrich. Ascorbate (As) was used as the reducing reagent and hydrogen peroxide was used as the co-oxidant.

EXAMPLE 1 Charging the Chelix 0.7 g of dry Chelix (capable of binding 1.4 mmol of divalent cations) was mixed in a 15 ml tube with 10 ml of either a 0.1 M solution of Fe2 (SO4)3 (corresponding to 1.0 mmol of Fe2 (SO4 )3) or 10ml of a 0.1M CuSO4. After 10 min of incubation the Chelix is washed 3 times with 10 ml of water and 4 times with 10 ml of buffer (phosphate 25 mM, pH 7.0). Each round of washing included (i) a centrifugation step (5000 rpm for 3 min) to sediment the Chelix, (ii) decanting of the supernatant and (iii) addition of washing solution followed by resuspending of the beads by whirl mixing. After the final wash the charged beads were resuspended in 5 ml of phosphate buffer.

The charged resin was light brown in the case of iron charging and dark blue in the case of copper charging.

A control Chelix (uncharged resin) was prepared exactly as described above with the exception that no iron was added.

This resin was colourless.

EXAMPLE 2 Generation of ROS on a surface that has chelated iron The following reactions were set up.

Absorbance at 520 nm 1. 1 ml of Mu + 250 g1 uncharged Chelix + 200 1 water. 0.5878 2. 1 ml of Mu + 250 y1 uncharged Chelix + 100 y1 As (o.lM) + 100 1 H202. 0.4062 3. 1 ml of Mu + 250 N1 Fe charged Chelix + 200 p1 water. 0.6109 4. 1 ml of Mu + 250 81 Fe charged Chelix + 100 N1 As (0.lM) + 100 g1 H2O2 (0.lM) . 0.3316 After mixing the reactions were left at room temperature overnight after which the absorbance of the murexide was recorded at 520 nm. Some bleaching of Murexide was observed in the control reaction (reaction 2, absorbance = 0.4062) with uncharged resin/ascorbate and hydrogen peroxide (compare reaction 1 and 2). This bleaching effect was attributed to the presence of trace amounts of divalent metal ions in the water used in the experiments. However, when the charged resin was used the bleaching effect increased significantly (reaction 4; absorbance = 0.3316) indicating that the bleaching effect was due to metal binding to the chelating surface and consequently production of ROS. The production of ROS was further supported by the observation that the light brown colour of the Fe-resin changed to dark brown during the reaction (oxidation of resin).

EXAMPLE 3 Generation of ROS on a surface that has chelated copper An experiment similar to that in Example 2 was set up, but using copper ions and less charged resin. The bleaching effect was recorded after incubation at room temperature after 3 hours.

Absorbance at 520nm 1. 1 ml of Mu + 50 81 uncharged Chelix + 400 N1 water. 0.9004 2. 1 ml of Mu + 50 N1 uncharged Chelix + 100 N1 As (0.lM) + 100 g1 H202 (O.lM)+ 200ml of H20 0.6574 3. 1 ml of Mu + 50 81 Cu charged Chelix + 400 l water. 0.4752 4. 1 ml of Mu + 50 g1 Cu charged chelix + 100 N1 As (0.lM) + 100 N1 H202 (0.1M) + 200ml of H20 0.0706 Again some bleaching was observed in the control reaction (reaction 2) with uncharged resin/ascorbate and hydrogen peroxide (compare reactions 1 and 2). Also, the bleaching increased significantly when the ion charged resin was used.

Compared to the Fe experiment in Example 2, the bleaching effect observed with Cu was substantially larger.

EXAMPLE 4 Bi ol ogi ca 1 experiments 2.5 g of Chelix was charged to the maximum capacity with Cu, Fe, Zn or Ni, respectively. Washing 5 times with water and 4 times with 25 mM phosphate buffer, pH 7.0. Each of the charged Chelix resins and an uncharged resin (control) were resuspended in culture tubes with 10 ml of LB growth media containing 10 p1 of an overnight culture of E. coli strain JM103. The culture tubes were incubated in a gyroshaker at 370C and inspected visually for growth at various time intervals. After 24 hours a substantial growth inhibition of the E. coli was observed in the culture tube containing the Cu charged Chelix compared to the culture tube containing uncharged resin. The clearest reaction was observed with Cu, and a lesser effect was found for Fe, Zn and Ni.

To ascertain that the growth inhibition observed with the Cu resin was not due to free copper in the solution (which may have a toxic effect on the bacteria) the amount of possible free Cu ions in the culture solution was analyzed by mixing 1 ml of Murexide (75 NM or 75 nmol) with 50 or 200 N1 of culture solution. No Cu induced W-shift of Murexide was observed. Since a W shift can be observed with 7.5 NM Cu in this assay this means that the 200 p1 E. coli culture contained less than 37.5 NM of free Cu ions. A concentration of free Cu ions of 100 NM was subsequently shown to have no effect for E. coli growth. We conclude that the observed effect of Cu was due to Cu bound to the resin and therefore was the result of generation of ROS.

REFERENCES 1. Torreilles, J., M-C Guerin and M-L Carrie. 1989, Biochimie, 71, 1231-1234.

2. Hirotsu, T., S. Katoh, K. Sugasaka, M. Sakuragi, K. Ichimura, Y. Suda, M. Fujishima, Y. Abe and T. Misonoo. 1985, Journal of Polymer Science: Part A: Polymer Chemistry, 24, 1953-1966.

3. Valentine, J.S., C.S. Foote et al. (eds.) Active Oxygen in Biochemistry, Chapman & Hall (London) 1995.

4. Wahl, M.. 1989, Marine Ecology.Progress Series, 58, 175189.

Claims (24)

1. A method of controlling in an aqueous, humid or intermittently humid environment the accumulation of organisms or organic matter on a surface, the method comprising associating with said surface a chemical system which in the presence of an oxygen source and a reducing agent is capable of continuously generating reactive oxygen species in biocidally active amounts, the system comprising (i) a redox active transition metal ion and (ii) at least one chelating compound which binds to the metal ion, the metal ion being so firmly associated with the chelating agent that it essentially does not dissociate into the aqueous environment.

2. A method of impairing the viability of organisms in an aqueous, humid or intermittently humid environment, where that environment is in proximity to a surface, said method comprising associating to said surface a chemical system which in the presence of an oxygen source and a reducing agent is capable of continuously generating reactive oxygen species in biocidally active amounts, the system comprising (i) a redox active transition metal ion and (ii) at least one chelating compound which binds to the metal ion, the metal ion being so firmly associated with the chelating agent that it essentially does not dissociate into the aqueous environment.

3. A method according to claim 1 or 2 wherein the metal ionbinding compound is a chelating compound selected from the group consisting of EDTA, ECTA, EHPG, HOEDTA, CHCEDG, CH3EH PG, CDTA, EHCHG, NTA, HEIDA, DTPA, EHPG and DHEG.

4. A method according to claim 1 or 2 wherein the metal ionbinding compound is a neutral chelating compound

5. A method according to claim 4 wherein the chelating compound is in the form of a hydroxylamine derivative.

6. A method according to claim 1 or 2 wherein the metal ionbinding compound is a chelating compound comprising a substituent moiety which is capable of binding to the surface whereby the chelating compound is fixated thereto.

7. A method according to claim 6 wherein the substituent moiety comprises a lipophilic group.

8. A method according to claim 6 wherein the substituent moiety comprises an anthraquinone group.

9. A method according to claim 1 or 2 wherein the chemical system is incorporated into a paint or a coating composition or into a fish net composition.

10. A method according to claim 1 or 2 wherein the chelating compound is fixated to a paint or a coating after the polymerisation leading to the paint or the coating composition.

11. A method according to claim 10 or 11 wherein said paint or coating composition comprises a biocide compound.

12. A method according to claim 1 or 2 wherein the surface is selected from the group consisting of a ship's hull, a water storage reservoir, a waste water reservoir, the inner surface of a water pipe or tubing for transportation of liquid media, a liquor container, a fish net, an anchor, a rope, a roof, a fence, a boat, a submarine, a water inlet or outlet of a power station and other industrial plants, an aqueduct, a canalised waterway, a submerged marine structure, an industrial processing tank, an air conditioning system, a filter, a medical bandage or plaster, a packaging foil, a film, a plastic, paper for storage of foods and fluids, a medical device, a pharmaceutical, a household or industrial appliance and a book.

13. A method according to claim 1 or 2 wherein the system comprises an oxygen source and/or a reducing agent.

14. A composition which when associated with a surface is capable of controlling the accumulation of organisms and organic matter on said surface when placed in an aqueous, humid or intermittently humid environment, the composition comprising a chemical system which in the presence of an oxygen source and a reducing agent is capable of continuously generating reactive oxygen species in biocidally active amounts, the system comprising (i) a redox active transition metal ion and (ii) a compound which binds to the metal ion, the metal ion being so firmly associated with the chelating agent that it essentially does not dissociate into the aqueous environment.

15. A composition which when associated with a surface is capable of impairing the viability of organisms in an aqueous, humid or intermittently humid environment, the composition comprising a chemical system which in the presence of an oxygen source and a reducing agent is capable of continuously generating reactive oxygen species in biocidally active amounts, the system comprising (i) a redox active transition metal ion and (ii) a chelating compound which binds to the metal ion, the metal ion being so firmly associated with the chelating agent that it essentially does not dissociate into the aqueous environment.

16. A composition according to claim 14 and 15 wherein the metal ion-binding compound is a chelating compound selected from the group consisting of EDTA, ECTA, EHPG, HOEDTA, CHCE DG, CH3EHPG, CDTA, EHCHG, NTA, HEIDA, DTPA, EHPG and DHEG.

17. A composition according to claim 14 or 15 wherein the metal ion-binding compound is a neutral chelating compound

18. A composition according to claim 17 wherein the chelating compound is in the form of a hydroxylamine derivative.

19. A composition according to claim 14 or 15 wherein the metal ion-binding compound is a chelating compound comprising a substituent moiety which is capable of binding to the surface or to a component of the composition whereby the chelating compound is fixated thereto.

20. A composition according to claim 19 wherein the substituent moiety comprises a lipophilic group.

21. A composition according to claim 19 wherein the substituent moiety comprises an anthraquinone group.

22. A composition according to claim 14 or 15 which is a paint or a coating composition.

23. A composition according to claim 22 wherein said paint or coating composition comprises a biocide compound.

24. A composition according to claim 14 and 15 which comprises an oxygen source and/or a reducing agent.