Environmental Engineering Reference
In-Depth Information
10.3 MICROPLASTIC DEBRIS
A relatively recent concern in the marine environment is the widespread
occurrence of microscale particulate plastics or microplastics (Cole et al.,
2011; Thompson et al., 2004). While the size range that is considered
“micro-” is not well defined in the literature, there is growing agreement
on “microplastics” being defined as debris in the size range of 1 µm to 1
mm. Other sizes of debris would then fall in different categories as follows:
nanoplastics = <1 µm; mesoplastics = 1 mm to 2.5 cm and macroplastics 2.5
cm to 1 m. Virgin resin pellets, an important component of beach debris,
size ranges is important because their interactions with marine plankton,
especially via ingestion, will be size-dependent.
Microplastics have been isolated from surface water, mid-water, marine
sediment, and beach surface in all the world's oceans (Moore, 2003).
Majority of the studies have used neuston plankton nets (333 µm mesh size)
on surface waters to collect and enumerate samples. Because of the mesh
size ofnetsused,mostofthefragments collectedare greater than 300 µmin
size. Depending on the location, anywhere from less than 10 particles/m
3
to
10
3
particles/m
3
of seawater has been reported (highest ever count is ~10
7
m
2
surface). The collection and quantification of microplastics in the ocean
has been recently reviewed (Hidalgo-Ruz et al., 2012).
Isolation of micro- and mesoplastics from debris samples that also include
biomass is particularly difficult. Floatation (or density-based separation)
alone does not completely isolate the plastic fragments from marine debris.
Digestion of sample to solubilize and remove the biomass has been
suggested: acid digestion (Andrady, 2011; Claessens et al., 2013), alkaline
hydrolysis (Jin et al., 2009), and peroxide digestion (Nuelle et al., 2014)
have been used. Recently, proteinase-K digestion was demonstrated to
solubilize greater than 97% (wt) of the biomass with no apparent effect on
the plastic fraction (Cole et al., 2013). The technique might also be used to
isolate ingested microplastics from zooplankton samples as well. Chemical
digestion does not affect most of the common thermoplastics except for
some condensation polymers such as polyamides and polyesters.
