Determination of minimum effective release rates of antifoulants by membrane perfusion

Antifouling (AF) coatings are designed to prevent biofouling by releasing bioactive compounds over 5-7 years at a controlled rate. Because biocides are also toxic to non-target organisms, environmental damage may result. Release rates of biocides in most AF paints are probably several times higher than necessary to prevent significant fouling. Decreased release rates could lessen environmental damage. This research was to determine the minimum release rate of biocides which will prevent significance growth of a test organism. Known fluxes of tributyltin biocide were released through a microporous membrane in flowing seawater; its effect was measured on peritrich protozoans. A higher flux was needed to prevent fouling by peritrichs than to keep off hard foulers like barnacles and bryozoans. Other biocides probably will be needed to control slime films. This method may have much wider applications in studying effects of substances diffusing from surfaces on settlement and survival of marine organisms.