A Brief Background on Antifouling Products and Poseidon’s Antifouling Program
Nontoxic antifouling compounds, substances which repel marine life but do not harm the environment, are the focus of Poseidon’s research. Knowing the history of biofouling will help you understand more about the impetus for Poseidon’s quest for the discovery of an effective antifoulant.
In the marine environment, all surfaces are affected by the attachment of fouling organisms, such as bacteria, algae and invertebrates including barnacles and mussels. These fouling organisms contribute to the corrosion of submerged surfaces. The efficiency of ships traveling through the open sea is particularly hampered when biofoulers, such as algae, clams and barnacles, are attached to the bottom. Barnacles need to be sandblasted away from the surface during dry docking of the ship prior to painting the hull. Expensive dry-docking, increased fuel costs and corrosion are important economic factors that mandate the prevention of barnacle attachment to the underwater surface of ships.
The Use of Toxic Chemicals
In the old days of wooden sailing ships, antifouling methods include use of arsenic, lime and mercurial compounds to prevent shipworms and barnacles from destroying the hull. Although organotin compounds were synthesized almost 150 years ago, it was not until the 1960’s when tributyl tin (TBT) first appeared in marine paint formulations. By the 1970’s, most ships were coated with some form of antifouling paint containing tin and copper. The shipping industry relies heavily on the use of TBT impregnated marine coatings that disperse into the sea at damaging rates. Such marine paints are cheap, very effective and preferred by the industry.
Biofouling organisms are killed upon contact with such painted surfaces, thereby preventing fouling for periods ranging from 6 months to 5 years depending upon the composition of the paint and the amount of heavy metals present.
The Environmental Consequences
Heavy metals are responsible for environmental damage to both terrestrial and marine life. In the marine environment, the continuous leaching of heavy metals has been responsible for the destruction of shellfish populations, sex changes in invertebrates and possible genetic defects in other marine animals.
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The International Maritime Organization (IMO), an Agency of the United Nations, acted on the increasing reports of toxicity to non-target organisms by adopting a resolution in 1990 recommending measures to eliminate antifouling paints containing TBT. It took eight more years (1998) before a resolution was passed for a global prohibition on the application of organotin compounds which function as biocides in antifouling marine paints. In 2002, an international treaty was signed that bans the application of paint containing tin on all ships beginning 1 January 2003 and the complete prohibition on the presence of organotin on all ships by 1 January 2008.
The Future of Antifouling Paints
There have been a number of new developments in antifouling paint through technological innovations originating in the paint industry. However, these ‘eco-friendly’ paints that are tin-free contain, instead, very high concentrations of copper, zinc or combinations of these with other toxic biocides. Moreover, these new paints are two to three times more expensive than TBT based paints. The toxic chemicals copper and zinc will eventually be phased out because of environmental problems and Poseidon sees the future of antifouling in non-toxic chemicals which employ a repellent action rather than a toxic mechanism. Typical biocides now in use are non-specific, this means they will kill other organisms which come into contact with the material. Repellents, on the other hand, will prevent attachment because the animal perceives the surface to be unpleasant and moves away without any cellular damage.
Poseidon’s Antifouling Program
Poseidon’s research in antifouling began as part of an overall program to develop environmentally friendly repellents. Studies began in 1987 to screen natural compounds that displayed potential repellant action against mosquitoes (and other biting insects), sharks, and fouling invertebrates. A chemical library comprising several thousand chemicals was screened and their bioactive substances were selected for further testing. A continuing research and development program was then designed to select the most active compound, to develop synthetic technologies for manufacturing the compound, then to formulate development and field testing for the new substance in marine environments.
Fouling organisms are cultured in artificial raceways and painted panels are exposed for various durations of time. Field research stations, such as the one shown here, serve as testing grounds for painted panels exposed to seawater rich in barnacles, oysters, clams and other biofouling organisms. The culture of macro-algae and micro-algae are also maintained here.
An in vitro screening system developed by Dr. Daniel Rittschof at Duke University Marine Laboratory (Beaufort, North Carolina) that utilizes laboratory-reared barnacles was employed to select effective repellents. Larvae or cyprids are collected and natural compounds (such as NB17, a series of naturally occurring compounds with antifouling properties) are tested in an assay that measures the settlement of the barnacle larvae on surfaces. The critical step in barnacle fouling is the period when the cyprid larva is selecting the appropriate surface to attach. Once attached, dislodging the larvae becomes difficult because it secretes one of the strongest adhesive known to man to secure it to the surface. A typical assay result for NB17 is shown on the left.
In December 1995, Poseidon completed the first series of studies at SHMRC, under the direction of Dr. Avelin Mary, demonstrating the efficacy of NB16 and NB17. These compounds prevent the attachment of barnacles when incorporated into marine paints at concentrations as low as 0.1 microgram per gram of paint. On a panel of 40 bacteria normally associated with biofouling, these compounds were found to be highly bacteriostatic.
More importantly, when tested against larval organisms, these compounds prevented attachment but did not cause death to the organism even when exposed for a long duration of time.
In 1998, Poseidon completed field studies to validate the efficacy of NB17 compounds when incorporated into paint formulations . These compounds were found to inhibit the attachment of algae to surfaces coated with NB17 compounds. Most notably, barnacles were prevented from attachment when NB17 was substituted in the place of tributyl tin paint formulations.
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In 1999, Poseidon also completed studies on a series of related compounds with similar repellent effects on barnacle larvae, thus completing critical gaps in our understanding of the structure-activity relationships in the selection of repellent chemicals. In 2000, the first patent application was filed with the United States Patent Office. A Patent Cooperation Treaty application was filed in 2001.
NB17 can be made available in thousands of tons and in adequate volume to support the needs of the paint industry.
Poseidon intends to enter three major markets – The first is the use of NB17 as an additive in paints for the recreational yacht market. The second is the industrial applications market for the shipping industry. The third is the aquaculture and fisheries industries which need coatings for nets used in fish culture and fishing.
Poseidon also provides testing services using in vitro barnacle settlement assays and panel testing to assist other companies interested in evaluating new products or new biochemicals.