Ballasting outside port to prevent spread of butyltin from merchant ships

Most international discussions on ballast water management onboard ships have been virtually on the prevention of the transport of biotic alien species. This study focuses on how to improve this limited knowledge regarding the transport of butyltin compounds via ballasting. Butyltin compounds in ballast water, extracted from three sea-going merchant ships with similar voyage routes and berth ports but with different ballasting practices, were determined. Only monobutyltin (8–57 ng l^?1) and dibutyltin (10–32 ng l^?1) onboard two general cargo ships were detected in the ballast water taken outside the ports. In contrast, significant tributyltin (23–93 ng l^?1) was detected onboard the container ship in the ballast water pumped inside the loading/unloading ports. The comparison results from this study indicate that the risk of tributyltin transfer may be effectively prevented by ballasting outside the ports.