Environmental Engineering Reference
In-Depth Information
5.2 Plastics in Sea
Plastics in the sea are the constituents of marine litter or debris, which originate
either from natural phenomena or from anthropogenic activities both on land and
in the sea. Plastics (including plastic bags and plastic strapping) constitute one of the
most potential harmful marine debris encountered in the world's oceans and seas,
enclosed bays and coastal zones, posing major threats to the marine biodiversity
and to the health of the marine lora and fauna, aesthetics, navigation and overall
environmental quality.
Small round virgin plastic pellets (2-5 mm) are the raw plastic material from which
larger moulded plastic items are made [5]. Alternatively, small plastic fragments can
also be the result of successive degradation processes acting on larger pieces of plastic
debris in the environment [6]. Plastics can take hundreds of years to break down, so
they may continue to entangle and kill animals year after year.
It has been estimated that over 13,000 pieces of plastic litter are loating on every
square kilometre of ocean today [7] and the plastic bags make up approximately
11% of the general marine litter [8].
In a 1998 survey, 89% of the litter observed loating on the ocean surface in the
North Paciic was plastic. In the Central Paciic Gyre, 6 kg of plastic for every kilo
of surface plankton was reported [7]. About 3,500 plastic resin pellets per km² have
been reported loating in the Sargasso Sea. Near industrial centres in New Zealand,
concentrations of up to 100,000 pellets were observed in one km² of beach. In 1990,
American scientists reported a 200-400% increase in the number of pellets present in
the North Atlantic Ocean from 1972−1987 [7]. The plastic materials, accumulating
in the ocean over decades, are believed to have broken down into microscopic
particles that are now washing up on beaches, loating in coastal and ocean waters,
and settling in the sediment.
5.2.1 Sources - Land-based and Sea-based (including Industrial,
Domestic and Others)
Plastic debris originates from a wide and diverse range of sources. Estimates suggest
that much of what is found at sea originates on the land. The effect of coastal littering
and dumping is compounded by the rivers and storm drains discharging litter from
the hinterland. These materials persist in the environment for a long time as they are
not biodegradable. However, in the ocean the plastics are weathered, and broken
up into smaller fragments, which eventually are reduced to tiny pieces the size of
sand grains. These particles are suspended in the surface of the seawater and settle
