Marine Pollution – Ballast Water

When marine pollution is mentioned, the immediate thoughts of most people will run to the horrific pictures of the various oils spills which have been so widely publicised. Those with empathy towards animals will also recall the sad images of oil covered sea birds , penguins and seals. If you are a bit more environmentally conscious and widely read , you will also think of plastic litter , fishing line and illegal seine nets which have found their way into the marine environment and entangled both birdlife and fish , whales and dolphins etc with dire consequences. Other pollution emanates from the land in the form of rubbish sewage and chemicals which are washed into the sea from rivers. Overall – WE ARE NOT VERY NICE TO OUR ENVIRONMENT!



All of the above are very serious but have been very widely addressed and everyone is very conscious of them but are there any other “hidden forms of pollution? Is there something we are missing? This article will address a very different, but equally dangerous form of pollution which , until fairly recently (over the last 30 or so years) was relatively unrealised. – This is the story of Ballast Water. When a ship is loading, discharging or sailing, she has to be kept stable at all times – for obvious safety reasons. She must be balanced and kept as low down in the water as possible. Unfortunately , not all cargo is either heavy enough or balanced enough to enable the ship to achieve this, so ships are fitted with special tanks situated at various positions which can be filled with water to various degrees to assist with this.

The diagrammatic below gives a very simple picture of the process involved This is an essential operation but brings with it inherent ecologically sensitive problems. Seawater is not sterile and therefore any organisms present at the port of loading, will be transported to the port of discharge. Such organisms will include not only microbial organisms such as bacteria and fungi and the like, but even small fish and mollusks. These will not necessarily be compatible with local organisms at the area of discharge. They can attack or destroy the local ones or , even if they are not particularly aggressive, they can still displace the local ones simply because the natural predators present are not partial to eating these “foreigners”. This means that they can just multiply , unchecked and flood the local ecology with their presence, The result can be that the local food chain is disrupted as they compete with their local equivalents for food and the locals start dying off – predators higher up the chain then die off as well until you are literally left with a “marine desert”! – The local fishing industry collapses and all the ancilliary industries surrounding are also disrupted.

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Eventually, economies of entire countries – especially the smaller, island nations, can be totally wiped out! Some examples of this are: Zebra mussels (Dreissena polymorpha) which are small, fingernail-sized mussels native to the Caspian Sea. These tiny creatures have invaded and taken over large areas of the Canadian great lakes and have now also made their way into many Canadian and US waterways , creating havoc with the local ecological balances The Comb Jelly a jellyfish-like species (Mnemiopsis leidyi), was introduced to the Black Sea from the eastern seaboard of America in the early ‘80’s. Its diet includess fish larvae and the tiny animals small fish feed upon. It rapidly reached a total mass of 900 million tons (ten times the annual fish harvest from the entire world!).


The dumping of solid waste, overfishing of resources and poorly controlled developments along the coastline have not helped either. Toxic Dinoflagellates (phytoplankton) –in various areas of the world. Microscopic organisms, known collectively as Toxic Dinoflagellates or phytoplankton, also known as algal blooms, create havoc in many areas of the world – especially where seafood is consumed in great quantities. These organisms often cause phosphorescence in the water and this a good indicator when NOT to eat seafood – caution must of course always be exercised when eating seafood. These are one of the principal causes of seafood poisoning but many can also be fatal. Tiny incompatible crab species have also been spread in this way and so have many other types of live organisms and fish What can be done to prevent this? Unfortunately, the answer is – NOT much!


In respect of ships, a special section or the United Nations Marine pollutant division (MARPOL) of the International Maritime Organisation is busy looking at this on an ongoing basis and have introduced various legislation to govern what ships may or may not do. One of the most popular and efficient forms of control at the moment is a deepsea exchange of ballast water. The release of the ballast water in mid ocean , not only exposes the various organisms to higher levels of salt which actually kills them but this also does not allow the organisms to gain purchase on rocks , walls etc and they sink to the bottom of the ocean where they cannot do much harm to land based ecological systems. The fresh seawater which is loaded in its place is safer , as organisms which live in it are then exposed to low concentrations of salt when discharged and, not being used to it , the majority also die off.

If your appetite for this subject has been whetted, there are many websites covering this subject and a google search for Ballast Water will open them to you. Other methods which were suggested were , chemical sterilization of the water (similar to swimming pool chemicals) – the release of this water after use introduces toxins to the water which may also kill off “friendly” species. Heat in the form of steam infusion – but this may damage sensitive cargo stowed adjacent to the ballast tanks and filters on both the inlet and outlet pipes but these will not block micro organisms.

Bilge Water is also guilty to an extent but , as this is usually mixed with a certain amount of oil, fuel waste etc , it is more of an oil than an organism threat and , fortunately is of very much lower quantity and does break down eventually if discharged deep sea (illegal) but this is usually collected by waste disposal companies who dispose of it responsibly (we hope)For more on this subject , see related posts on this site – Bentley

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