Effects of operational and accidental pollution

Up until the time that MARPOL came into effect it was recognised that, while accidental pollution provided devastating local effects, it was the general operations of ships which caused the greater amount of pollution.

General operations included unrestricted dumping of garbage, unwanted chemicals (including nerve agents, nuclear waste and explosives) sewage and the cleaning of cargo tanks at sea. Cargo tanks used to be cleaned at sea by washing with seawater and disposing the residue over the side.

With reference to the AMSA and IMO websites some definitions and effects of pollution are listed below.


“Oil” means petroleum in any form including crude oil, fuel oil, sludge, oil refuse, and refined products (other than petrochemicals which are subject to the provisions of Annex II of the present Convention) and, without limiting the generality of the foregoing, includes the substances listed in Appendix I to this Annex.
“Oily mixture” means a mixture with any oil content.
Noxious Liquid Substances
A Noxious Liquid Substance is any chemical listed in the International Code for the Construction and Equipment of Ships carrying Dangerous Chemicals in Bulk (the IBC Code) and in the Schedules to the Protection of the Sea (Powers of Intervention) Act 1981(Cth) which can be accessed at the AMSA website.
Categories of hazardous substances require increasing levels of control:
  •   Level X – Major hazard to marine life and human health – discharge prohibited
  •   Level Y- Hazard to marine life and human health – discharge strictly limited
  •   Level Z – Minor hazard to marine life and human health – discharge limited
  •   Other – Substances not listed in X,Y or Z and present no hazard to marine life and human health – no controls

Packaged Harmful Substances in Packaged Form

Harmful substances are those substances which are identified as marine pollutants in the International Marine Dangerous Goods Code (the IMDG Code). Packaged Form refers to the form of containment specified in the IMDG code.

MARPOL and Marine Orders specifically prohibit the dumping or washing overboard of prohibited substances.


Sewage means drainage and other wastes from any form of toilet or urinal, medical premises or compartment containing animals (MARPOL Annex IV Regulation 1).

Treated sewage is described as sewage that has been contaminated and disinfected (MARPOL Annex IV Regulation 9 and 11). NSW codifies the standard of that treatment, in Schedule 4 of the Marine Pollution Regulations (NSW) 2006, into counts of the faecal coliform, suspended solids and biochemical oxygen demand.

The discharge of raw sewage into the sea can create a health hazard, while in coastal areas; sewage can also lead to oxygen depletion and an obvious visual pollution - a major problem for countries with large tourist industries.

The main sources of human-produced sewage are land-based - such as municipal sewers or treatment plants. (IMO Website)


The definition of Garbage in MARPOL Annex V Regulation 1 is:

Garbage means all kinds of victual, domestic and operational waste, excluding fresh fish, generated during the normal operation of the ship and liable to be disposed of continuously or periodically except those substances which are defined or listed in other Annexes

The IMO website provides the following information on garbage at sea.

Garbage from ships can be just as deadly to marine life as oil or chemicals.

The greatest danger comes from plastic, which can float for years. Fish and marine mammals can in some cases mistake plastics for food and they can also become trapped in plastic ropes, nets, bags and other items - even such innocuous items as the plastic rings used to hold cans of beer and drinks together.

It is clear that a good deal of the garbage washed up on beaches comes from people on shore - holiday-makers who leave their rubbish on the beach, fishermen who simply throw unwanted refuse over the side - or from towns and cities that dump rubbish into rivers or the sea. But in some areas most of the rubbish found comes from passing ships which find it convenient to throw rubbish overboard rather than dispose of it in ports.

For a long while, many people believed that the oceans could absorb anything that was thrown into them, but this attitude has changed along with greater awareness of the environment. Many items can be degraded by the seas - but this process can take months or years, as the following table shows:

 Time taken for objects to dissolve at sea:


Paper bus ticket


2-4 weeks


Cotton cloth


1-5 months




3-14 months


Woollen cloth


1 year


Painted wood


13 years


Tin can


100 years


Aluminium can


200-500 years


Plastic bottle


450 years


Air Pollution

Ships emit Sulphur Oxide, Nitrogen Dioxide and Carbon Dioxide gases into the atmosphere from exhaust fumes.

Some ships also had on board incinerators, for the disposal of garbage and packaging, and installations containing ozone depleting substances such as refrigerants and fire retardants

Ballast water

Large vessels such as container ships and tankers have ballast tanks which are loaded and unloaded to maintain the stability or balance of the ship whilst adding or removing cargo.

When ships take up water in one part of the world and discharge it another they translocate invasive marine species and water borne diseases such as jellyfish, crustaceans, algae and cholera.

It is estimated that about 10 billion tonnes of ballast water is transferred globally each year, potentially transferring from one location to another species of sea life that may prove ecologically harmful when released into a non-native environment.

Modern tankers must now have protective segregated ballast tanks that are completely separate from the ships cargo and fuel system. There are also strict rules about how ballast water is taken in or discharged, including the flushing of ballast tanks at sea.

Australia has Mandatory Ballast Water management requirements and ships entering Australian waters must declare their ballast water as part of the usual quarantine process of entering port.

Ballast water is assessed as high risk when taken up in a foreign coastal sea and low risk when taken up in fresh water, Australian water or mid ocean. High risk water is prohibited form being discharged in Australian waters.

Ships are prohibited from carrying ballast water in cargo tanks except on the rare occasions where the weather is so severe as to warrant it to preserve the safety of the ship.

In this case the ballast water can only be carried in tanks that have been properly washed and the waste or residue discharged ashore prior to leaving port. Cargo tanks are cleaned using crude oil washing or chemical tank washing procedures as set out in MARPOL.

When ballast is subsequently discharged from these tanks it must be discharged ashore or comply with the requirements of discharge at sea under MARPOL Annex I and II.


Biofouling is the accumulation of marine organisms (plants or animals) that attach to objects immersed in salt water (such as vessels’ hulls, ropes, anchors and other equipment). These marine organisms can be harmful to local marine ecosystems and guidelines are now in place to manage the marine pest risks from biofouling.

Projects are underway to investigate treatment options for biofouling of vessels’ internal water systems and to develop standards for antifouling systems.