Sea to source

Litter enters the ocean from diverse point and diffuse sources, which can be both land-and ocean-based. It can also be transported over long distances before being deposited onto shorelines or settling on the bottom of the oceans and seas. Source identification can be very difficult, especially when the litter item has remained in the marine environment for a long period. Certain items, in particular fragments resulting from the disintegration of larger items, can be very hard or even impossible to identify in terms of their initial purpose and possible origin. One of the commonest general categorisations of the origin of ML items is the division between sea-based and land-based input. Sea-based origin relates to litter that is
directly (accidently or purposely) released into the sea by maritime activities e.g.
shipping, fishing, offshore installations or dumping of refuse at sea. Land-based origin relates to activities which cause littering directly on the coast, such as beach tourism, but can also refer to litter generated in more distant areas, such as towns and industrial sites, and blown or washed into the sea. Litter entering the environment via sewage outlets is considered as having a land-based origin, even though most sewage outlets are situated in rivers or discharge directly in to the sea. Similarly, riverine litter is sometimes considered to be land-based, even though some of the littering can occur by boats and ships navigating rivers. Some easily identifiable items have a clear function and can be attributed, with a high
level of confidence, to specific industrial or consumer sectors (e.g. tourism, shipping,
fishing, effluent treatment) or points of origin. Fishing nets and pieces of fishing net are obvious examples of items, which can be attributed directly to a specific sector i.e. the fishing industry and cotton-bud-sticks are an example of a well-known point of origin i.e. improper disposal down the toilet by consumers. However, many litter items cannot be directly connected to a particular source, way of release or pathway. Some items can have a number of potential sources and pathways of entry as well as geographic origins. For example, plastic drinks bottles can be left on beaches by tourists locally, thrown overboard by merchant shipmen, disposed of improperly in-land and washed into the sea through storm water overflows. They can also enter the sea via rivers and, because they are buoyant, can be easily transported into a given area by water currents and prevailing winds. Measures to combat the
amount of plastic bottles in the marine environment will need to consider all these aspects in order to be effective.

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