At sea, ships will burn some of their rubbish in an incinerator. An incinerator is a special fire box designed to burn paper, card and some food rubbish. It cannot burn metal or glass. Ships are not allowed to throw overboard any plastic material. Other rubbish may not be thrown overboard closer than 12 km from shore.
Some plastic can last longer than 100 years in sea water. Plastic can be found in all oceans around the world including the Antarctic seas; most of it comes from the land and not from ships. Plastic bags are particularly harmful to marine animal life like turtles and sea birds. These creatures can mistake plastic bags for jellyfish, which are an important source of food for them.
It is much better if ships don't throw any rubbish overboard at all. It is best that their incinerator is used or dispose of rubbish in waste containers when they reach their next port.
Ports supply bins for rubbish and recycling bins for other waste that can be recycled. In Australia only ships operating solely between Australian ports can recycle their waste. Quarantine regulations are designed to prevent new diseases and pests coming into Australia on ships coming from other countries. Rubbish from ships coming from foreign countries goes to special quarantine rubbish tips where it is buried.