BACKGROUND OF THE INVENTION The growth of marine organisms on the hulls of vessels has been a problem since sea faring began."Hull fouling"is a natural phenomenon and a term for the colonisation of the submerged parts of a vessel's hull by individuals or colonies of species of sessile marine invertebrates. These species are not inherently different from those that might locally occur on natural substrates ; the term"fouling"was simply coined to distinguish assemblages on natural hard substrata (eg reef, rock, sunken logs, submerged lava flows) from those growing on artificial manmade surfaces (eg pilings, pontoons, underwater cables, hulls etc.). The presence of hull fouling can lead to a considerable increase in fuel consumption in engine powered vessels, and a significant decrease in the speed of the vessel. It is thus highly undesirable for commercial ships operating in world of competition. More important however, from an ecological and conservationist point of view, is the risk of species transfer and invasion by hull fouling. The transfer of marine sessile organisms by hull fouling is brought about when larvae of a species settle upon the hull of a vessel which subsequently sails to a new, possibly distant destination. The physical (eg hydrodynamic drag) and physiological (eg lack of food, changes in temperature and salinity) stress imposed on the organism during the transfer and upon arrival at the new destination may lead

to an unsuccessful introduction, but in many cases the organism is able to survive in the new environment. The reproductive stages of a hull fouling adult population may become established as"invaders"in the novel habitat. The subsequent geographical spread of marine invasive species can have disastrous impacts on native ecosystems.

Since the early ages of shipping, seafarers have tried to develop various sorts of"antifouling"systems that were aimed to prevent marine growth on their vessels' hulls. The number of approaches have been great, ranging from the appliance of waxes or tar to the submerged parts of the hull to completely covering the hull in copper sheathing. However, their success was not often overwhelming, as fouling could never be prevented over a long time frame. Since the beginning of the 20't-century, the most common form of antifouling system has been a protective paint that is applied to the submerged parts of a vessel's hull. Over the years, the complexity of these systems as well as their performance has seen an amazing increase. The most popular and effective marine antifouling paints are based on compounds of copper and/or tin. However, these paints often contain a significant number and concentration of heavy metals, which has led to considerable chemical pollution of a large number of marina and port environments. Since their development in the 1970s, paints based on inorganic tin compounds (mainly tributyltin (TBT)) have been the most effective antifouling systems ever developed ; incorporated into self-polishing paint types they can prevent fouling on a vessel for up to five years. However, TBT released into the water by these paints has been shown to accumulate especially in benthic sediments and its accumulation in the tissues of marine biota can have disastrous consequences on the reproduction and viability of many organisms, including commercially important species. As a consequence of these impacts, TBT based paints were banned from use on vessels of less than 25 m in length in the early to mid 1980s in a number of

countries including France, the UK, New Zealand, Japan and Australia. Due to ongoing ecological impacts, some countries are now considering the total ban of TBT paints from larger commercial ships as well.

Since the initial bans in the 1980s, the marine paint industry has tried to develop new, non-tin based, equally efficient antifouling systems, but with little success. Current paints for vessels of less than 25 m length are mainly copper based and their performance is poor compared to TBT based antifouls.

A new trend among paint developers is to now strive not only for long temporal performance of the paints but also for increased environmental friendliness. Trends in this research include physical and electrochemical research into the prevention of adhesion of marine invertebrates and the incorporation of organic bioactive compounds, or biological toxins, into antifouling paints.

An extensive number of products have been identified and tested especially in the last decade, and screening of a large number of marine organisms has resulted in the isolation of a significant number of promising bioactive compounds. However, to date, the demand for an environmentally friendly antifoul has not been satisfied.

SUMMARY OF THE INVENTION In a first aspect, the present invention provides an anti-fouling composition for application to a substrate intended for use in an aquatic environment, the composition including a biocide and a binder arranged, in use, to release the biocide from the composition over a period of time, wherein the biocide is selected from tea tree oil, lemon scented tea tree oil, cloned tea tree oil, lemon myrtle oil, eucalyptus oil, components/extracts thereo-, and mixtures thereof.

The substrate is any man made object to be used in an aquatic, typically marine, environment. The substrate will typically be the hull of a boat or ship but may also be underwater cables, pilings, pontoons etc.

Tea tree oil, lemon scented tea tree oil, cloned tea tree oil, lemon myrtle oil and eucalyptus oil are essential oils. The biocide may include component (s)/ extract (s) of the essential oil (s) rather than the essential oil (s) per se. The biocide may also include a mixture of essential oil (s) and component (s)/extract (s) of essential oil.

The composition may contain additional components such as pigments, plasticisers and, in the case of water based emulsion systems, coalescents. For enhanced biocidal efficacy, the composition may also include biocides other than those referred to above.

A preferred biocide is tea tree oil, lemon scented tea tree oil, a mixture thereof or components/extracts thereof. Set out below in Tables 1 and 2 respectively are the chromatographic profile for tea tree oil from the Australian Standard and a typical analysis of the components of lemon scented tea tree oil.

Table 1 Components Minimum % Maximum % terpinolene 1. 5 5 1, 8-cineole-15 a-terpinene 5 13 ! y-terpinene 10 28 I p-cymene 0. 5 12 i terpinen-4-ol 30- a-terpineol 1. 5 8 limonene 0. 5 4 sabinene Traces 3. 5 aromadendrene Traces 7 b-cadinene Traces 8 globulol Traces 3 lui viridiflorol Traces 1. 5 a-pinene 1 6 Table 2 a-thujene trace a-pinne 0. 4 sabinene Trace ß-pinene 0. 1 myrcene 0. 4 methyl heptanone 0. 4 limonene 0. 1 trans-ß-ocimene Trace terpinolene 0.1 linalool 1. 8 iso-pulogol 2. 4 citronellal 18. 6 cis-iso-citral 0. 6 terpinen-4-ol 1. 1 trans-iso-citral 1. 3 citronellol 4. 5 neral 23. 3 geranial 26. 2

The binder is typically a polymeric resin normally used for paint or coating applications. The polymeric resin may be modified with non-polymeric resins such as rosin or cellulosic resins.

The anti-fouling composition may be produced by mixing the biocide with a binder such as one-part epoxy, acrylic and similar vinyl polymers.

The binder may be a so-called two-pack coating, such as two-pack epoxy coatings. Typically, a two-pack binder will have a resin component (Part A) and a cross- linking component (Part B). In such cases, the antifouling composition may be produced by mixing the biocide with Part A to form a two-pack antifouling composition. Immediately prior to use, Part A is mixed with Part B and the mixture is applied to a target substrate such as the hull of a boat. Part A typically contains solvent, pigment,

additives and finely dispersed biocide. Mixing of Part A and Part B results in cross-linking to form a matrix within which the biocide is held.

Without wishing to be bound bv theory, it is believed that following application of the anti-fouling composition to a substrate, a thin film of the biocide resides at the exposed surface of the applied anti-fouling composition and that over time further of the biocide migrates to the surface film which prevents, or at least mitigates, build-up of aquatic plants (eg. algae) and aquatic animals (eg. barnacles) on the surface of the applied anti-fouling composition. Again without wishing to be bound by theory, it is believed that the biocide affords ani-fouling properties both chemically and physically.

Physically, it is believed that the surface film of the biocide renders it difficult for aquatic plants and animals that might attach to the applied anti-fouling composition to remain attached because they are swept away from the applied anti-fouling composition on removal of the surface film due to interaction between the substrate and the aquatic environment, for example, by action of tides, currents and movement of the substrate through the aquatic environment. Chemically, it is believed that the biocide interferes with cellular membranes of aquatic organisms to disrupt normal activity.

Advantageously, the anti-fouling composition may have a low solvent level, for example less than 3% by volume solvent, due to the thinning effect of the biocide.

The biocide of the present invention may also find application in non-aqueous environments, for example, as a component of a paint for use in high fungal growth situations or medical environments where sterility is advantageous. Accordingly, in another aspect, the present invention provides a biocidal composition for application to a substrate, the composition including a biocide and a binder arranged, in use, to release the biocide from the composition over a period of time, wherein the biocide is

selected from tea tree oil, lemon scented tea tree oil, cloned tea tree oil, lemon myrtle oil, eucalyptus oil, components/extracts thereof, and mixtures thereof.

EXAMPLES Example 1 An anti-fouling composition was prepared by thoroughly mixing four parts by volume of a modified epoxy resin which contained 18. 1% by volume tea tree oil with one part by volume polyamide resin. The epoxy resin had an epoxide equivalent rating of 250-400, a viscosity in the range 1500-5000 mPsc, and was 75-90% non-volatiles.

The polyamide resin was a modified amido amine resin having an amine equivalent weight o-95, a viscosity in the range 500-1500 mPsc and was 100 % non-volatiles. The resulting anti-fouling composition which contained 15 % by volume tea tree oil was applied as a coating to strips of steel which were subsequently placed in a marine environment. The strips of steel were inspected after six months in the marine environment and exhibited no buildup of organisms.

Example 2 An antifouling composition was prepared with a 50 : 50 mixture of tea tree oil and lemon-scented tea tree oil Leptospermum citratum (petersonii) in lieu of the pure tea tree oil of the composition of Example 1. In all other respects, the composition was identical to that of Example 1.

Experimental panels were prepared from marine plywood (170 x 170 x 12 mm) which were coated with two layers of West Systems Marine Epoxy Resin. Three successive thin layers of the antifouling paint were then applied to selected panels using a paint roller brush to give a total antifoul thickness of the order of 350-500 um. There was a 25-35 minute interval between individual coats, and all the panels were left to cure for approximately 48 hours prior to submersion.

A small central hole was drilled into each panel and four panels (two treated and two control) were then

mounted onto a T-shaped frame made up of 20 mm PVC pipes using 40 mm stainless steel self tapping screws. Four such frames collectively carrying 8 panels coated with the antifouling paint and 8 control panels painted only with the two layers of West Systems Marine Epoxy Resin were suspended off floating jetties in the Townsville Breakwater Marina, Townsville, Australia.

Panels were suspended in a horizontal orientation because previous recruitment experiments had indicated that both recruitment density and taxonomic richness are greater in a horizontal rather than a vertical orientation. The Townsville Breakwater Marina was chosen as the incubation site because, as indicated by previous experimentation, it is the single most severe site for recruitment of fouling organisms in the Townsville region. The incubation period was four weeks.

Recovery of the panels after the incubation period indicated that there were clear differences in total biotic cover and the size of individuals or colonies between treatment and control panels. After 4 weeks exposure, antifouling paint coated panels had a mean bare space of approximately 59 % ; whereas, virtually all available space had been overgrown on the control panels.

Photographs of a control panel and a treated panel feature as Figures 1 and 2 respectively.

The following taxa were encountered on the control and treatment panels : Colonial ascidians, solitary ascidians, serpulid, spirorbid, and sabellid polychaetes, encrusting bryozoans, erect/creeping bryozoans, bivalve mollusks, barnacles, and filamentous algae. All of these taxa were observed on both treatment and control panels.

However, two facts were apparent : (1) only a subset of the above taxa occurred on each painted panel, whereas all of them occurred on each control panel, and (2) individuals (in particular barnacles and sabellid polychaetes) and colonies (encrusting bryozoans and colonial ascidians) had attained a substantially larger size on control panels than

on painted ones.

Example 3 A length of timber was completely coated with two layers of West Systems Marine Epoxy Resin. A transverse strip of the timber was subsequently applied with three layers of the antifouling composition of Example 2. After 48 hours curing, the timber was submerged in the Townsville Breakwater Marina. A photograph of the subsequently retrieved length of timber features as Figure 3 in which the difference in biotic cover between the transverse strip which had been coated with the anti fouling composition and the remainder of the timber is readily apparent.