Rapid degradation of two antifouling agents in seawater as affected by plankton and dissolved oxygen

Abstract Environment-friendly antifouling agents are the key research and development directions for marine antifouling paints. The characteristics for excellent performance by an antifouling agent are a good antifouling effect, long-period function, and little impact on the aquatic environment. Based on comparison with 4,5-dichloro-2-octyl-4-isothiazolin-3-ketone (DCOIT), the degradation of bio-based 2,5-furandiformaldehyde oxime (E-DFFD) and bio-based 2,5-furandimedoxime copper (II) complex (E-DFFD-Cu), which are two new antifouling agents developed by our laboratory, was analysed in seawater environment, and their environment-friendly characteristics were investigated via biodegradation experiments. The results showed that the presence of plankton and a high concentration of dissolved oxygen (DO) could greatly promote their degradation rate and amount, resulting in rapid degradation in seawater, i.e., with aeration, 12.23% and 32.23% of the agents degraded in natural seawater after 7 days, respectively, (as compared to 5.50 and 14.81% without aeration), the contrast was similarly apparent in sterile seawater which shows 9.93% and 29.61% decrease after filtration and sterilization. The half-life periods of E-DFFD-Cu and E-DFFD in natural seawater at 22°C were 12.4 and 34.7 days, respectively. Furthermore, the influence of the structure and composition of different plankton groups on their degradation amount and rate was significantly different, and the dominant biological groups for biodegradation changed when the antifouling agent was modified and derived. Zooplankton was the main contributor to degradation of E-DFFD, accounting for 80.84% of its biodegradation and 68.35% of its total degradation. Phytoplankton was the main contributor to E-DFFD-Cu degradation, accounting for 53.24% of the total biological contribution, followed by bacteria (31.47%). Bacteria accounted for 50.56% of the total biological contribution to DCOIT degradation followed by zooplankton (27.23%), and abiotic factors accounted for more than 10% of its total degradation. Nonetheless, abiotic factors had little effect on the degradation of E-DFFD-Cu and E-DFFD. This study evaluated the contribution of marine organisms to the biodegradation and the influence of DO to degradation of two environment-friendly antifouling agents in natural sweater.