Surface weathering and changes in components of microplastics from estuarine beaches
2017
Microplastics are a type of emerging environmental pollutant that
has been the subject of increasing concern worldwide. The surface
morphology, composition and changes in the distribution of microplastics
in the environment are poorly understood. The corresponding research
methodology is also at the exploratory stage. Here, we examine typical
estuarine sediments from Shandong Province, east China, that are influenced
by intensive human activity. The microplastics are separated from
the sediments using an apparatus of continuous flow and floating separation.
The microplastics samples are processed to determine the types, morphology
and changing composition of microplastics present using a range of
advanced microscopic and micro- analytical methods. The aim is to
understand the weathering and subsequent surface changes in the microplastics
under the environmental conditions of estuarine sediments. Optical microscope and scanning electron microscope-energy spectrum
(SEM-EDS) analysis shows that foams and pellets, together with fragments,
fibers and films, are present in the estuarine sediments. The five
shape types of microplastics had different weathering surface morphologies
compared to the corresponding large plastic debris from the same sampling
sites and to the corresponding commercial plastic products. The surfaces
of the commercial products are smooth. The surfaces of plastic debris
appear to be slightly broken and aged while the surface of microplastics
from the same sites show many more microholes, cracks or protuberances.
This indicates that the surfaces of microplastics on the estuarine
beaches have been strongly weathered. Scratches, creases, microholes,
cracks, either concave or convex and of various shapes and sizes were
found on the surfaces of microplastics from the coastal environment,
possibly due to mechanical friction, chemical oxidation and/or biological
attack. Attenuated total reflection Fourier transform infrared spectroscopy
(ATR-FT-IR) was used to find oxygen-containing functional groups such
as carboxylic acids, aldehydes and esters or ketones on the microplastic
surfaces from the tidal flats on the basis of polymer component analysis.
The two selected shape types, namely foams and fragments from soft
plastic woven bags, had different infrared spectra than their corresponding
large plastic debris from the same sampling sites and to the original
commercial plastic products. The surfaces of these two microplastics
had more complicated infrared spectra near the fingerprint area. This
implies that the aging process of large plastic debris may be an important
source of microplastics in the environment. A polymer blend of both
polyethylene and polypropylene was identified in the fibers using
pyrolysis gas chromatography-mass spectrometry (pyr-GC-MS). The pyr-GC-MS
analysis also indicates that the pyrolysis products were much common
on the aged surfaces of foams from the beach than on the inner part
of foams after removal of the aged surfaces, including mainly compounds
containing oxygen or nitrogen such as oleanitrile, trans-13-docosenamide,
α-n-normethadol; 1,1-diphenyl-spiro [2,3] hexane-5-carboxylic acid, methyl ester, hexadecanoic acid, octadecyl
ester and hexadecanoic acid, hexadecyl ester. The surficial morphology,
composition and possible properties of microplastics from the estuarine
beaches were clearly different from those of the original commercial
plastic products. We suggest that surface weathering can cause changes
in the surface components of microplastics under the actual conditions
prevailing on coastal beaches. By observation of the weathering of
microplastic surfaces it is difficult, using a single identification
method, to distinguish between finer polymer components, particularly
in samples of blends or copolymers. This study shows that pyr-GC-MS
can be used directly to obtain and verify the specific weathering
products of microplastics and the ATR-FT-IR may be used as an ancillary
tool for recognition of microplastics in the environment. Much effort
needs to be devoted in the future to understanding the changes in
surface processes, ecological and environmental effects, and methods
of identification of microplastic particles in coastal and oceanic
environments.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
0
References
12
Citations
NaN
KQI