Solid waste

It has been estimated that there are over 17,000 pieces of plastic litter floating on every square kilometre of the world's oceans. Solid waste, or litter, is dominated by plastics, but also includes glass, metals, and complex objects combining multiple substances, ranging from domestic and industrial appliances to ships. Of the total of some 8 million tonnes of solid waste entering the sea every day, about 5 million tonnes are thrown, or lost, from ships. The remainder comes from urban centres, and from remote centres of high affluence such as tourist centres. East Africa and the South Pacific have put solid wastes as second among their priority problems, second only to domestic sewage.

Buoyant and neutrally buoyant substances, have clearly received the most attention. These remain at or near the water surface, often for months or years, before becoming negatively buoyant and sinking (about 70% of all such waste) or being washed up on coastlines. Whilst at sea such solid waste can become an attraction to marine life, with larger objects often supporting a small ecosystem of attached organism and fish. Such objects may indeed be responsible for the transport of alien species to new areas . Other, usually smaller materials pose a threat to many marine species.

This solid waste can clearly be a hazard to shipping, and adds a considerable cost to the fishing industry. When washed ashore, large amounts of litter can present health hazards and this is also very detrimental to the recreation and tourist industries.