Environmental Engineering Reference
In-Depth Information
10.3.1 Primary and Secondary Microplastics
Meso- and microplastics can be of either primary or secondary in origin.
The primary microplastics enter the ocean already as microscale particulate
material. The same is true for some of the mesoplastics; for instance, virgin
plastic prils or pellets enter the oceans as accidental spills during transport
and also with runoff from plastic processing operations (Doyle et al., 2011;
Ogata et al., 2009). Industry is making an effort at minimizing the loss of
virgin pellets to control their influx into the sea. Small plastic beads that
are used in sandblasting (beads used in place of sand) are also washed into
the oceans. These microplastics may even carry metal residues picked up
fromtheiruse.Somecosmeticformulationsincludemicrobeadsaswellused
as an exfoliant in their formulations (Fendall and Sewell, 2009). Another
significant source of microparticles and microfibers is that from laundering
synthetic fiber clothing (Browne et al., 2011). A single garment laundered in
a washing machine can shed nearly 2000 microfibers. In all these instances,
pre-formed microscale plastic enters the ocean environment.
Secondary meso- and microplastics on the other hand are generated in
the marine environment itself, derived from the weathering degradation
of larger plastic debris (Andrady, 2011; Gregory and Andrady, 2003).
Breakdown of plastics in the environment due to extensive photo-induced
oxidation facilitated by sunlight is well known. Oxidative processes in
plastics are likely localized to surface layers exposed to solar UV radiation.
Plastics products and virgin prils typically have smooth surfaces. Plastic
debris on beaches as well as in water, however, are well known to show
uneven surface textures including pits, cracks, and flaking (Cooper and
Corcoran, 2010) due to weathering degradation. The microcrack pattern
is generally indicative of weathering damage as opposed to mechanical
fragmentation (Zbyszewski et al., 2014). Similar surface cracks often
develop in plastics exposed to UV radiation in the laboratory (Akay et al.,
1980) with LDPE (Küpper et al., 2004; Tavares et al., 2003), polycarbonate
(Blaga and Yamasaki, 1976) and polypropylene (Qayyum and White, 1993;
Yakimets et al., 2004). Micrographs illustrating the surface textures are
shown in
Figure 10.3
.
It is reasonable to assume that missing fragments
from these surface textures contribute to marine micro- and nanoplastics.
With virgin plastic pellets that have no UV stabilizers in them, the
weathering process is relatively fast compared to that in plastic products. A
weakened, embrittled, microcracked surface can readily fracture, shedding
off microplastics due to water movement, abrasion against sand, or due to
