Abstract: 

In the marine environment, biofouling often refers to the unwanted attachment and growth of marine organisms on artificial surfaces, which can cause significant challenges in marine related industries. To prevent biofouling, biocidal compounds were often mixed in coatings and applied to artificial surfaces. However, some of these biocides were later considered unacceptable to the environment, eventually led to global or regional prohibition of their uses. Despite growing environmental concerns, limited bioactivity and ecotoxicity studies exist on several antifouling compounds previously believed to be ecofriendly. This study investigated the antifouling bioactivities and non-target toxicity of two compounds approved under the official coating guidelines of the China Classification Society: medetomidine and N(2,4,6 trichlorophenyl) maleimide. Given the chirality of medetomidine, its more potent form in antifouling assay (dexmedetomidine) was used. Through antifouling bioassay based on four typical biofouling species: the barnacle Amphibalanus amphitrite, the bryozoan Bugula neritina, the polychaetae tubeworm Hydroides elegans and a biofilm-forming benthic algae from the genus Navicula, the antifouling performance of dexmedetomidine and N(2,4,6 trichlorophenyl) maleimide were characterized for the first time and compared with their toxicity against non-target organisms. Based on current results generated from A. amphitrite and B. neritina, it was evident that (1) dexmedetomidine inhibited A. amphitrite settlement at parts-per-trillion level, but it only inhibited B. neritina at parts-per-million level, where it exhibited board-spectrum lethal toxicity; suggesting its ecofriendly properties was limited to barnacles only (2) N(2,4,6 trichlorophenyl) maleimide demonstrated higher toxicity against non-target organisms that both A. amphitrite and B. neritina, indicating more environmental risk assessment was needed to further assess its suitability as a commercial antifouling biocide.