When we think of marine pollution, the things that spring immediately to mind might be engine emissions or oil leakages into the sea.
Yet there is another form of ‘pollution’ that ships can be responsible for – biological pollution that results in invasive life forms being transported around the world and released into new sea areas, disrupting the local ecosystems.
It’s all down to ballast water and how it is used and released. Ballast water is pumped aboard vessels to maintain safe operating conditions throughout a voyage. It offers several benefits - reduces stress on the hull, improves stability, improves propulsion and manoeuvrability and compensates for weight changes throughout the voyage.
The problems occur when ballast water ends up being discharged in a completely different part of the world. Plankton, bacteria, plants and molluscs can all end up in a new environment.
Invasive species can out compete native ones, alter ecosystems and change coastal landscapes. Did you know there is even a Japanese sea worm that has neurotoxins more powerful than arsenic or cyanide?
To prevent these damaging invasions, ships are required by the IMO to have an approved Ballast Water Management Plan or BWMS. They must carry a ballast water record book and carry out ballast water management procedures to a given standard. The cleaning and discharge of bilge water is also regulated and the composition and location of both ballast and bilge water discharges must be recorded and reported.
The MARPOL regulations set a maximum limit of 15ppb for oil concentrations in bilge water for it to be discharged into the sea. The regulations also govern the discharge of wastewater from other parts of the ship such as scrubber sludge.