Under the International Convention for the Prevention of Pollution from Ships, cruise ships are barred from dumping plastics anywhere at sea and floatable garbage within 25 miles of shore. They are permitted, however, to dump garbage that has been ground into pieces larger than one inch when they are three miles from shore and unground garbage when they are at least 12 miles form shore.
Toxic chemicals generated by cruise ships are generally waste products from photo developing, dry cleaning, painting and other activities. Under the Resource Conservation and Recovery Act, ships are required to store these wastes onboard while under way, and then, once in port, to transfer them to certified chemical treatment and disposal facilities.
In the wake of the Exxon Valdez disaster, the Oil Pollution Act amended the Clean Water Act to prevent oil dumping by ships. Any oil coming from a ship within 12 miles of shore must be diluted enough so that it leaves no "visible sheen," which means it must measure less than 15 parts per million (ppm).
Once a ship is more than 12 miles from shore, it may release more concentrated oily waste, as long as it measures less than 100 ppm. The law also requires ships to retain oily waste onboard while under way and then send it to an appropriate reception facility on shore. Ships also must record the disposal of oily residues and bilge water.
Cruise ships and other large marine vessels have diesel engines that are major sources of air pollution. One cruise ship discharges 1/5 tons of smog-forming nitrogen oxides, 1.3 tons of sulfur oxides (the equivalent of a large cement plant), 253 pounds of carbon dioxide, 100 pounds of volatile organic compounds and 75 pounds of particulate matter. This is equivalent to the output of 12,000 automobiles.
It is especially hazardous to persons with asthma and respiratory illnesses. However, emissions from cruise ship diesel engines are unregulated, except in Alaska. California enacted a law in September 2004 that prohibits incineration by cruise ships within three miles of shore.