Antifouling effect of hydrogen peroxide release from enzymatic marine coatings: Exposure testing under equatorial and Mediterranean conditions

Hydrogen peroxide (H2O2) may be considered an environmentally friendly antifouling alternative to common biocides such as Cu2O and various organic compounds. In this work, the efficiency of antifouling coatings releasing hydrogen peroxide via enzyme-mediated conversion of starch, under Mediterranean and equatorial climatic conditions, is investigated.

During seawater exposure of the coatings, starch is first converted to glucose by glucoamylase (rate-controlling step) and subsequently glucose is rapidly oxidised by hexose oxidase in a reaction producing hydrogen peroxide. The coatings formulated have been characterised in terms of common coating characteristics and immersed on rafts in seawater outside Singapore and Spain to monitor antifouling efficiency.

The results have been compared to results previously reported from temperate waters in the North Sea outside The Netherlands. Using laboratory assays, the transient hydrogen peroxide release rate from the coatings at different temperatures has been measured. The investigations are used to evaluate the ocean performance of the antifouling coatings.

Coatings can be formulated with starch/enzyme 'pigments' in considerable amounts and yet retain the mechanical properties required of an antifouling coating. However, the antifouling effect of the coatings immersed in seawater near Singapore and Spain, when inspected after 8 and 14 weeks, respectively, is insufficient.

In comparison, previous studies under colder conditions showed an effect exceeding that of two commercial references over 67 days. The release rate of hydrogen peroxide from the coatings is shown to be greatly influenced by temperature, and therefore the results provided here suggest an antifouling effect that is highly dependent on the environment of the coating.