Minimum effective release rate of antifoulants (2): Measurement of the effect of TBT and zosteric acid on hard fouling

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Abstract
A membrane perfusion device for determining minimum effective release rates (MERR) of antifouling agents is described. The technique is applied to known biocidal agents and to a new prospective natural antifouling agent. This method allows controlled and reproducible release rates to be achieved independent of water chemistry and flow near the immersed surface. Unlike constant concentration methods, the device acts similarly to a painted surface, allowing establishment of diffusion gradients, thereby allowing fouling organisms to exhibit natural chemotactic responses to the released toxin. The method was applied at four remote sites to natural populations of fouling organisms. The MERRs of known (tributyltin chloride, dibutyltin chloride, and cupric ion) and experimental (zosteric acid) AF agents were determined. The effective release rates of cupric ion and organotin were consistent with immersed panel data and field observation of ship hulls, while the effective rate of zosteric acid, determined at two test sites, was much higher. Such data provide coatings formulators with valuable information relating to the suitability of an agent for AF coating use.