Tannin capsules: a promising antifoulant

DELADINO L.; NAVARRO A.S.; MARTINO M.N.; ROMAGNOLI R.; GARCÍA M.; STUPAK M.; PÉREZ M.

Río de Janeiro, Brasil

Congreso; XIII International Congress on Marine Corrosion and Fouling; 2006

International Congress on Marine Corrosion and Fouling

Protection of ship-hulls from marine fouling organisms is essential for efficient operations and energy conservation. To achieve this, ship hulls have been coated with antifouling paints that contain toxic material, such as copper and organotin, and create an environmental hazard due to continuous release of toxic materials. New strategies are being developed that use non-toxic or natural compounds to control fouling growth. Encapsulation provides protection against environmental conditions, like pH, temperature and chemical substances, and is the most chosen method for controlled release of a wide spectrum of active compounds. The objective of this work was to encapsulate Quillaja saponaria tannins and to study their release in sea water. Capsules were obtained by ionic gelification between sodium alginate (2% w/w) and calcium chloride (0.05 M); the alginate solution contained 0.01 g/ml of tannin. Then the formed calcium alginate beads were immersed in a chitosan solution (2% w/w). Interaction between the chitosan, a cationic polysaccharide, with the negatively charged alginate resulted in the formation of a membrane. Different immersion times (30 and 60 min) in CaCl2 and in chitosan (30 and 60 min) solutions were analyzed. Then the beads were dried at room temperature. Release assays were performed sinking twenty dry capsules in test tubes with 10 ml of sea water. The tannin concentration released was determined by UV spectrophotometric measurements at 280 nm (Beckman DU 650 USA) during 30 days. Percentages of tannin release in sea water were 29% w/v (30 min in CaCl2 + 30 min in chitosan) and 31% w/v (60 min in CaCl2 + 60 min in chitosan); the rate of tannin release was 0.01 mg/ml.day in both cases. In the lab, capsules of Quillaja saponaria tannin were assayed for antifouling properties on Polydora ligni larvae by incorporating them into hard, stable gels (PhytagelTM). In addition, the inhibitory effect of seawater solution tannin on these larvae were also determined. For field trials, gel replicates were suspended from floating docks at Mar del Plata harbour, for 28 days. Bioassays shown that quillaja tannin capsules and tannin solution affected Polydora ligni larval survival. When organisms were in contact with tannin solutions, a rapid immobilization of appendages and loss of phototactic response occurred, these effects were faster as tannin concentration was higher. On the other hand, larval response was similar for all cases, i.e. no difference was observed between different immersion times in CaCl2 and in chitosan solutions. Field trials shown similar results, i.e. Polydora ligni did not build tubes on gels. In conclusion, 1) encapsulation is an excellent method to evaluate antifouling properties of high soluble compounds and 2) Quillaja tannin has an inhibitor effect on Polydora ligni settlement.