108
D. J. Sarkar et al.
4.5.2 Raman Spectroscopy
Raman spectroscopy was also used to identify plastic particles. Here also, it is combined with microscopy and a spatial resolution of 1 µm can be achieved (Löder
and Gerdts 2015). The identification by spectroscopic method (FT-IR and Raman)
is affected by the environmental-driven changes on the surface of plastic material or
by the presence of additives. Therefore, microbial fouling, humic acid adsorption,
presence of colouring pigments, etc., interfere with the absorbance, reflectance or
excitation of the plastics and sometimes lead to the misidentification of the particles
(Lambert and Wagner 2018).
4.6 Aquatic Risk Assessment of MPs
Since the size of MPs is the most important factor, the risk assessment due to MPs
could be based on the same. The MPs of varying particle size possess different risks
to the aquatic organisms. Fish may avoid larger plastic particles but have the risk of
ingestion of small MPs (<5 mm) while feeding. Through trophic transfer, the plankton
eating fish may encounter MPs with size range from nanoscale to 5 mm or more and
thus possess a huge effect on ecological health (Tanaka and Takada 2016). It has
been described that floating MPs with less density are mostly associated with lower
organisms, viz. phytoplankton and zooplankton, whereas benthic invertebrates viz.
polychaete worms, amphipods, molluscs and echinoderms show more association
with MPs with high density. Thus, higher vertebrates such as fishes also swallow
MPs from these lower organisms and benthic vertebrates through prey-predation
relationship. Occurrence of MPs was estimated in the sediments of some of major
river systems, for example, Rhine River (228–3760 items/kg) (Klein et al. 2015),
Beijiang River (178–544 items/kg) (Wang et al. 2017), Thames River (185–660
items/kg) (Horton et al. 2017), Ganga River (99.27–409.86 items/kg) (Sarkar et al.
2019), and it has been found that the dominant plastic debris was found to be PE, PP
and PET, which are reported to be the most dominant plastic debris in the rivers of
Asia and South East Asia. The most important morphotypes of the plastic particles
were found to be the films and fibres. More recently, MPs contamination with fibres is
being emphasised as compared to the other morphotypes like films and beads. It was
revealed in some reports that the major source of these fine fibres are garments which
are released to aquatic system through washing of same (Napper and Thompson
2016).
The differential sources of primary and secondary MPs have huge influences on
their risk management and regulatory options. Regulatory measures can successfully
minimise the risk associated with industrially produced primary MPs to acceptable
levels through regulating their point of production and use. Example of such upstream
regulation are US Microbead-Free Waters Act of 2015, which prohibits companies
to use microbeads in beauty and health products from 2017 (FDA 2017); UK bans on
microbead use from 2018 (GUV.UK 2018), etc. However, managing secondary MPs
pollution is much more challenging involving general action against all sort of plastic
D. J. Sarkar et al.
4.5.2 Raman Spectroscopy
Raman spectroscopy was also used to identify plastic particles. Here also, it is combined with microscopy and a spatial resolution of 1 µm can be achieved (Löder
and Gerdts 2015). The identification by spectroscopic method (FT-IR and Raman)
is affected by the environmental-driven changes on the surface of plastic material or
by the presence of additives. Therefore, microbial fouling, humic acid adsorption,
presence of colouring pigments, etc., interfere with the absorbance, reflectance or
excitation of the plastics and sometimes lead to the misidentification of the particles
(Lambert and Wagner 2018).
4.6 Aquatic Risk Assessment of MPs
Since the size of MPs is the most important factor, the risk assessment due to MPs
could be based on the same. The MPs of varying particle size possess different risks
to the aquatic organisms. Fish may avoid larger plastic particles but have the risk of
ingestion of small MPs (<5 mm) while feeding. Through trophic transfer, the plankton
eating fish may encounter MPs with size range from nanoscale to 5 mm or more and
thus possess a huge effect on ecological health (Tanaka and Takada 2016). It has
been described that floating MPs with less density are mostly associated with lower
organisms, viz. phytoplankton and zooplankton, whereas benthic invertebrates viz.
polychaete worms, amphipods, molluscs and echinoderms show more association
with MPs with high density. Thus, higher vertebrates such as fishes also swallow
MPs from these lower organisms and benthic vertebrates through prey-predation
relationship. Occurrence of MPs was estimated in the sediments of some of major
river systems, for example, Rhine River (228–3760 items/kg) (Klein et al. 2015),
Beijiang River (178–544 items/kg) (Wang et al. 2017), Thames River (185–660
items/kg) (Horton et al. 2017), Ganga River (99.27–409.86 items/kg) (Sarkar et al.
2019), and it has been found that the dominant plastic debris was found to be PE, PP
and PET, which are reported to be the most dominant plastic debris in the rivers of
Asia and South East Asia. The most important morphotypes of the plastic particles
were found to be the films and fibres. More recently, MPs contamination with fibres is
being emphasised as compared to the other morphotypes like films and beads. It was
revealed in some reports that the major source of these fine fibres are garments which
are released to aquatic system through washing of same (Napper and Thompson
2016).
The differential sources of primary and secondary MPs have huge influences on
their risk management and regulatory options. Regulatory measures can successfully
minimise the risk associated with industrially produced primary MPs to acceptable
levels through regulating their point of production and use. Example of such upstream
regulation are US Microbead-Free Waters Act of 2015, which prohibits companies
to use microbeads in beauty and health products from 2017 (FDA 2017); UK bans on
microbead use from 2018 (GUV.UK 2018), etc. However, managing secondary MPs
pollution is much more challenging involving general action against all sort of plastic