Further studies investigating a potential non‐leaching biocide using the marine fouling diatomAmphora coffeaeformis

The toxicity and degree of leaching of the antimicrobial agent 3‐(trimethoxysilyl) propyloctadecyldimethyl ammonium chloride (Dow Corning® 5700) incorporated as a crosslinker into silicone elastomer (SE) polymers has been studied using the test alga Amphora coffeaeformis. After a one‐week pre‐soak, cell viability studies indicated a toxic effect of DC5700 SE surfaces compared to the control SE. DC5700 SE surfaces leached for up to 20 weeks were also toxic to settled cells although toxicity of the surfaces was reduced after 23 week leaching in seawater. Coated slides were consecutively leached for 7 d intervals and the collected leachates inoculated with A. coffeaeformis cells for toxicity tests. Control SE leachates were non‐toxic to the cells with results not significantly different to untreated f/2 medium, leachates from DC5700 SE coated slides were significantly toxic for up to 14 weeks. Extraction and gas chromatographic separation of DC5700 SE leachate samples identified the presence of volatile components of DC5700. Soxhlet extraction of surfaces in boiling solvents was used to remove all uncrosslinked material from the polymers and created non‐leaching surfaces containing only crosslinked DC5700, but removing the leachable components removed all toxic properties. Thus the toxicity of the DC5700 SE surfaces was a result of leaching of uncrosslinked DC5700 from the coating and once all excess DC5700 had been removed the polymer retained no toxicity.