May 26 2011

Environmental Impacts of Antifouling Materials

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Biofouling is a major problem for all marine-related vehicles and industrial installations that are placed in marine environments (Boehlert and Gill). Biofouling is the aggregation of undesired organic and inorganic materials on marine surfaces (Hofford, Chemicals) Primary biofouling sources include sediments (inorganic) as well as microorganisms and macroorganisms (organic). Biofouling is problematic for marine industrial projects primarily because biofouling introduces the problem of drag on materials that are designed for efficiency. Biofouling, in relation to Ocean Thermal Energy Conversion (OTEC), can take place on the outer surfaces of pipes and sub-marine apparatus as well as water intake pipes. When the insides of pipes are fouled with water-borne material, the ability of pipes to uptake water is impaired which reduces the efficiency of the system as a whole, reducing the amount of energy derivable from the system. Biofouling also reduces the efficiency of heat transfer in systems (Thomas, Environmental Fate)

Major pollutive materials: Copper oxides ,Irgarol, Diuron
Antifouling paints are implemented in the design in order to reduce the effects of biofouling on marine materials. Typical antifouling paints consist of materials that make it difficult or undesirable for organisms to live on surfaces (Yebra, Diego). Tributyltin is one antifouling paint that was found to be effective at preventing the growth of organisms on marine surfaces. Extensive environmental impact assessments, however, proved that Tributyltin had negative impacts on the health and growth of oysters (Hofford, Chemicals).
Tributyltin has been replaced by Irgarol and Diurion, two photosynthesis inhibitors that are believed to be less damaging to organisms than Tributyltin. It has been found. However, that the organic biocide Irgarol 1051 can accumulate in areas that are frequented by boats and have a low amount of water exchange (mixing with outside water sources). While not toxic in low doses, the required toxicity for death of an organism is dependent on the size and nature of the organism. It has been found to have a five day EC50 of 0.136 micrograms per liter for a variety of microorganisms.
Diurion, like Irgarol 1051, has been found to persist in the environment after its introduction. It is, however, less persistent and has a half-life of 14 days. This is much less than the 100-350 day half-life of Irgarol 1051. Because it is so water-soluble, diurion is found primarily in dissolved form in water: little is bonded to surrounding sediments (Thomas, Environmental Fate).

^Comparative toxicity of Irgarol 1051 to organisms, ranging from algae to fish. Note the considerable jump in tolerable concentrations between microalgae and crustaceans. This highlights Irgarol’s ability to block biofouling organisms but not harm macroorganisms (Thomas, Environmental Fate).

Copper Oxides
The study of biocides in the environment has shown that biocides can exist in water in elevated concentrations if they do not degrade upon entrance into water. If biocides do not degrade upon entrance into water, they enter sediments and organisms. One substance that can enter sediments is copper oxide. In the ocean, copper is primarily locked within sediments because of its weight. It can be suspended into the water again by boat activity and storms. This sudden increase in copper concentration can be harmful to fish and other marine organisms (Thomas, Environmental Fate).