Chemical and physical treatment options to kill toxic dinoflagellate cysts in ships' ballast water

More than 5000 culture-produced resting cysts of the toxic marine dinoflagellate Gymnodinium catenatum were subjected to a wide range of chemical (chlorine, copper sulphate, hydrogen peroxide, pH, salinity and a commercial microbiocide) as well as physical (heat) treatments. Effective treatment to prevent germination of dinoflagellate cysts in seawater samples could be achieved with high concentrations of free chlorine (500 ppm) or hydrogen peroxide (5000 ppm). However. the high costs involved and environmental as well as ship' s safety considerations render these options impracticable as a routine treatment method for ships' ballast water (25 000 to 100 000 t capacity). In contrast, the heating of ballast water (30-90 s at 40-45°C) may provide an effective, environmentally friendly solution to the global problem of ballast water transport of unwanted marine organisms.