According to a study
by the US National Research Council, 46% of the oil entering the oceans come from marine transportation, either through accidents or deliberate discharges.
For example, many ships illegally discharge bilge oil (a mixture of water, oil, lubricants, and other pollutants that collect in a ship's hold) before entering a port as this is cheaper than disposing of it legally at the port.
Dumped bilge oil accounts for nearly 10% of all oil entering the oceans each year. On the eastern coast of Canada alone, dumped bilge oil kills at least 300,000 seabirds each year - more than the total number killed by the Exxon Valdez
oil spill in Alaska in 1989.
Shipping activities also accidentally release oil. Ports where trans-shipment of oil takes place, for example, suffer from a chronic release of oil through ship leakage, ship maintenance, or mishandling. This problem is often ignored, despite the fact that its cumulative effects may have significant effects on the surrounding ecosystem.
Many chemicals used in shipping operations also enter the ocean
These include cleaning agents, chemicals for water treatment, and chemicals in refrigerating equipment and fire-extinguishers.
Some of these chemicals are toxic, persistent, and bioaccumulative. This means they do not break down very readily in the environment, are absorbed by marine animals, and increase in concentration up the food chain. People also become contaminated by eating contaminated fish.
Evidence is mounting that a number of man-made chemicals can cause serious health problems - including cancer, damage to the immune system, behavioural problems, and reduced fertility.