Environmental Engineering Reference
In-Depth Information
and co-workers deine 'microplastics' as small fragments of plastics with a size of less
than ~50 μm in the sediments and water column [4]. However there is no universal
deinition for describing microplastics in terms of size. Use of the term microplastics
has been extended now to contain all plastic debris that are smaller than 5 mm in
size. Thompson and co-workers have documented that about 100 million kilograms
of microplastics are accumulated annually in the North Sea [5]. In the '
International
Research Workshop on the Occurrence, Effects, and Fate of Microplastic Marine
Debris
' held in September 2008 at Washington deined the term microplastics
as 'plastic particles smaller than 5 mm', and ranging from 333 μm to 5 mm.
The microplastics are further divided into two types namely, primary and secondary
microplastics. Plastic materials that are prepared in a microscopic size are called
primary microplastics. They are mostly used in facial, hand- cleansers and cosmetics.
Nowadays microplastics are used in the medical ield as a carrier for drugs, proteins
and other biomolecules. However, increasingly, the use of microplastics has replaced
traditionally used natural exfoliating material (ground almonds, pumice, apricot,
walnut husks and oatmeal).
Secondary microplastics are the products formed by the breakdown of large plastic
materials from sea and land. Plastic materials in the land and marine environments,
over a period of time lose their structural integrity, which results in their fragmentation
by the effects of physical, biological and chemical processes. Ultraviolet (UV) radiation
from sunlight causes oxidation of the polymer matrix that leads to bond breakage.
Plastics present in the marine environment (below the sea surface) have less chance
of photo-oxidation occurring, whereas plastic materials present on beaches have a
high chance of turning brittle, being cracked and degrading rapidly because of the
high oxygen availability and direct exposure to sunlight. This turns the plastic yellow,
results in the loss of their structural integrity and leads to fragmentation by the action
of the waves, abrasion and turbulence. This process is a continuous one, and ultimately
as the fragments become smaller over time they become microplastics and after some
time they become nanoparticles. The existence of nanoplastics in the ocean is likely
to be increasing everyday and in the coming years researchers have already started
to think about the impact of these in the marine food chain [6].
1.2 Marine Debris threatening the Flora/Fauna in the Sea
In addition to direct dumping into the ocean, solid waste material that reaches the
marine environment from rivers, drainage, the sewage system or by wind are called
'marine debris' [
7]
. Advances in the industrialised human society and changes of life
style has generated an enormous quantity of materials over the last 30−40 years, and
their amount is increasing even more because of the use of synthetic materials, namely
plastics. They are to be found loating everywhere in the world's oceans (from the
