Tannin and tannate from the quebracho tree: an eco-friendly alternative for controlling marine biofouling.

Current antifouling coatings are based on toxic compounds that can be harmful to the natural environment. A promising alternative to these compounds is the use of natural products that are non-toxic, but have antifouling properties. Tannins are natural, water-soluble, complex polyphenolic substances, which precipitate proteins and have anticorrosive and antimicrobial properties. In this study, the effect of quebracho tannin as a probable antifouling pigment in both laboratory and field trials is evaluated. As tannins have high solubility in aqueous media and consequently would leach rapidly, they were precipitated as aluminium tannate, which has an adequate solubility for use as a component in marine paints. In vitro exposure of Balanus amphitrite and Polydora ligni larvae to low concentrations of both quebracho tannin and saturated aluminium tannate solutions produced complete appendage immobilisation. In 28-d field trials of test gels, a significant decrease in micro- and macrofouling density and diversity in relation to the control gel was detected (p < 0.05). This study suggests that natural tannins could be employed as bioactive pigment for new antifouling technologies.