The potential effects of antifouling paints

Biocides

Sources of copper in the marine environment

The effects of copper in the marine environment

Boats spend a large proportion of their working life partly submerged in water. As with all objects subjected to long periods of time in the water, boat hulls become prone to colonisation by the many micro-organisms which inhabit the aquatic environment. This colonisation is known as fouling. The extent of infestation depends on a number of factors including water temperature, salinity and productivity of the organic matter on which the organisms feed.

Boat hulls are susceptible to all types of fouling irrespective of the material from which they are constructed. The fouling, if not attended to, causes increased drag on the hull, leading to increased fuel consumption, and can eventually cause significant damage to the boat structure. A heavily fouled vessel may also lose manoeuvrability. It is, therefore, necessary to apply some form of coating which will protect the hull against infestation. These coatings are generally known as antifouling paints and they are applied to the hull at regular intervals.

Antifouling paints usually contain a biocide, or toxin, held within the structure of the paint. The coating is designed to leach biocide slowly into the marine environment, preventing any organism adhering to the paint by poisoning the settling organisms.

The nature of a biocide is such that potentially it can have harmful effects, not only on the fouling organism it is designed to deter, but also on other marine life unconnected with fouling activity. It is the potential impact of these paints on marine life that is the subject of this section.

The Biocides

For many years tributyltin (TBT) was the favoured biocide for use in antifouling paints, although it was usually used in conjunction with other biocides such as copper. However, it became evident in the 1980s that its continued use was causing severe damage to shellfish communities and, in particular, dog whelk populations. This resulted in the implementation, in 1987, of a Europe-wide ban on the use of TBT in antifouling paints on boats under 25 meters. Its use is still permitted on craft over this length and in certain industrial and agricultural applications.

Before the widespread use of TBT, antifouling paints were commonly based on copper. The ban on TBT resulted in a shift back to paints which contain copper as the main biocide. Copper is included in antifouling paints most commonly as cuprous oxide, but also as cuprous thiocyanate and metallic copper powder. One of the main drawbacks of the return to predominantly copper based antifouling paints is that the copolymer type of paint, which was initially developed for use with TBT, is not as effective when used with copper biocides alone. Other drawbacks include its incompatibility with aluminium hulled craft and the relatively subdued colours that can be produced.

However, it is widely felt that although the performance of copper biocides cannot approach that of TBT, they remain the most effective of the alternatives for the foreseeable future. To achieve as high a performance as possible from current antifouling products, a 'booster' biocide is normally used as copper is not fully effective against all fouling species.

There is currently a great deal of research into alternative forms of biocides, particularly those of organic origin. These, however, tend to be less universally effective than other biocides and, in particular, may deter only specific types of fouling organism. As a result of these 'species-specific' characteristics, such biocides will almost always be used with other biocides, including copper. The organic biocides are also very expensive to develop and register. They are therefore usually developed and registered in other industries first, such as the agrochemicals industry, for use in other applications. Furthermore, although they are from organic sources there is no assumption that they are inherently less environmentally harmful than any other biocides.

Teflon based antifouling paint is also available, and has been used on racing yachts for a number of years. It is particularly suitable for racing due to its low friction surface, although it is not considered a particularly effective antifouling coating when used without a biocide. There has been some research into the use of silicon but this is at a fairly early stage and as silicon is rather soft it is not an easy material with which to work.

Antifouling paints utilising some form of copper biocide account for over 95% of the total antifouling market in the UK (personal communications) and this market share is likely to persist for a considerable time. It is on these antifoulants, therefore, that this section concentrates. This does not, however, imply that the other biocides are necessarily any more or less harmful, although there is little evidence available on their relative impacts.

Sources of Copper in the Marine Environment

Copper is a naturally occurring element and is essential as a trace element for metabolic processes in living organisms. However, it can also prove extremely toxic in high concentrations. Therefore if copper accumulates to a significant degree in the aquatic environment it can have a detrimental effect on marine life.

Copper is present in all human and animal wastes, and non-human activity, such as natural weathering, also leads to copper input into the environment. However, the major sources of copper contamination in inland and coastal waters are industrial wastewater discharges and atmospheric deposition, particularly from foundries and metal plating and cleaning operations. Fungicides, wood preservatives and boat antifouling paints can also contribute to high levels of copper in the aquatic ecosystem.

The Effects of Copper in the Marine Environment

Due to its complex nature and the uncertainty over its level of interaction with other substances, it is difficult to establish the precise effect of elevated levels of copper in the marine environment. Furthermore, although it may be possible to detect the presence of copper concentrations in sediments by sampling, it is rather more difficult to identify the source of such concentrations. Depending on the location, sediments can be highly mobile and resuspension of copper in the water column can result in the transportation of the metal to areas away from the main sources.

Therefore, before assumptions can be made concerning the impact of copper-based antifoulant on the marine environment, it is vital that further research is carried out. This should be focused on identifying the sources of elevated levels of copper found in the marine environment and establishing the exact nature of any subsequent environmental impact.

In 1984, a UK government commissioned report on copper, concluded that due to problems of quantifying the exact environmental effect of differing copper concentrations, it is difficult to generalise about the toxicity of copper to marine organisms. There is, however, evidence to show that certain species of fish and other marine organisms are sensitive to quite low levels of copper even though other species are relatively tolerant of much higher levels. Marine invertebrates are thought to be slightly more sensitive to copper than fish. Furthermore, evidence suggests that marine organisms have some capacity for adaptation to higher than normal levels of copper although sudden high inputs of the metal are likely to cause adverse effects in otherwise unexposed populations.

Significant copper accumulation is unlikely to occur in fast flushing open coastal areas, but can accumulate in the sediments of low flushing waters including streams, rivers and bays. The US National Oceanic and Atmospheric Administration found that between the late 1970s and 1990, levels of copper in marine organisms have steadily increased (World Resources 1992-93). This is an indication of increasing copper concentrations in the aquatic environment.

There are relatively few studies that specifically relate to the effect of copper based antifouling paints on the marine environment and none which examine the potential impact on the mSAC designated features. Those that do exist point to evidence of elevated levels of copper in the vicinity of shipyards and dry docks, whilst others found that marine organisms in the vicinity of a marina had higher levels of copper than those in an adjacent undeveloped bay.

The only research identified which specifically assesses the concentrations of copper in the vicinity of marinas is an undergraduate research project carried out at the University of Southampton (Newbold, 1993). This involved sampling sediment from several sites around Southampton Water to determine whether marina environments were associated with elevated concentrations of copper. The research found some evidence that copper based antifouling paints have an effect on copper concentrations on the surface sediment in the vicinity of the marinas sampled. However, due to the mobility of copper in the water column, it concluded that more research was required to determine whether the effluent from industrial processes in the area is contributing to such concentrations.

Some studies have been carried out into the effects of particular substances contained within copper-based antifoulants. For example, research into Ingarol 1051, a trizine herbicide used to boost the effectiveness of antifoulant paints, has suggested that it can result in reduced plant growth and a reduction in photosynthesis.

Some European countries including Denmark have now banned the use of certain biocides in antifouling paints. The bans have been based on evidence that such substances do indeed have a negative impact on the marine environment. However, this evidence is disputed by industry and other EU countries have been slow to follow suit.

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