Microplastics plastic waste is one of the most hot

Microplastics are
plastics of smaller size having diameter less than 5mm.Microplastic represents
the consequences of human activities in aquatic ecosystem. Although
microplastic (MP) pollution has widely reported in marine ecosystems, now MP pollution
in riverine ecosystem has also been reported in recent years. Formation of
microplastics is generally fall into two categories either by breakdown of
larger plastic objects (secondary MP) or direct use as resin pellets and using
micro beads of plastic in cosmetics and personal care products (primary MP).Smaller
size of microplastic makes it bioavailable for many organisms. It has potential
to bioaccumulate and acts as a vector for various pollutants and pathogens.
There are researches conducted on marine ecosystem but data on microplastic
pollution in riverine ecosystem is still scarce.

1.     Introduction

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Microplastics are
freshwater pollutants of emerging concern of current age, the age of plastic. Among the various human burdens on aquatic
environment and life, the built up of plastic waste is one of the most hot
issue worldwide. While plastics provide significant societal advantages (Andrady, A.L., Neal, M.A., 2011),
there are drawbacks to our ‘plastic age’. Microplastics are plastics of smaller
size having diameter less than 5mm.Formation of microplastics is generally fall
into two categories either by breakdown of larger plastic objects (secondary
MP) or direct use as resin pellets and using micro beads of plastic in
cosmetics and personal care products (primary MP) (Thompson et al., 2004; Fendall and Sewell, 2009; Browne et al., 2010,
2011). Breakdown of larger plastic objects (secondary MP) takes place by
various processes like degradation by microbial activities, sunlight reactions,
water reactions, redox reactions under different temperatures (Andrady, 2011).Strength, long
residence time in environment, unsustainable usage, and
improper
waste management, all these causes makes plastics as a pollutant of natural environment
(Barnes et al., 2009).

There is more
literature on microplastic pollution in marine ecosystem describing their
origin, amount, fate and impacts on oceanic life (Andrady, 2011; Browne et al, .2011; Cole et al., 2011) but limited
studies concentrated on effects of microplastic pollution in riverine and
freshwater ecosystem (Wagner et al.
2014).  Thus, little knowledge exists
on presence of microplastic in river water. Information about their origin,
abundance and fate is still rare but microplastic pollution impacts, source and
fate in environment are somewhat similar in marine ecosystem and riverine
ecosystem (Thompson et al. 2009;
Eerkes-Medrano et al. 2015).Microplastic pollution is considered as big
threat to freshwater ecosystem because of it smaller size which makes it
bioavailable for living organisms throughout the food chain
(Betts, 2008; Thompson et al., 2009a; Wright
et al., 2013b).It has pose a risk to bio accumulate as it decreases in size
(Thompson et al., 2004; Fendall and
Sewell, 2009; Browne et al., 2010, 2011).Microplastics are ingested by freshwater
invertebrates and fish(Rosenkranz et al.
2009; Imhof et al. 2013; Sanchez et al. 2014; Biginagwa et al. 2016) which
leads to negative impacts on them. In addition, number of chemicals involved in
the making of plastics (Dekiff et al., 2014) and it has
tendency to adsorb organic contaminants from the surrounding media
(Bakir, 2012). Through
the process of ingestion these chemicals transfer from one organism to another
and may acts as a carrier for other organic contaminants
(Zarfl C, Matthies M, 2010).

The main sources of
microplastic pollution in rivers are effluents of wastewater treatment plants,
outflow of sewage during high rain events, discharge of domestic sewage
containing facial cleansers and agricultural runoff containing plasticizers (Free et al., 2014). Studies have
proved that once microplastics enter into the body of organisms it has
potential to accumulate and microplastics are endocrinal disruptors which cause
many adverse health impacts, including high mortality rate, internal damages,
stress, lack of growth and development, suppressed immune system, tumor development
and dysfunction of metabolic activities (Rosenkranz
et al. 2009; Imhof et al. 2013; Sanchez et al. 2014; Biginagwa et al. 2016)neurological
problems, genotoxicity, energy imbalance, reduced feeding activities, and hormonal
disruption (Della et al.
2014; Besseling et al. 2014).

Although data on riverine ecosystem related
to microplastic pollution is scarce but now freshwater pollution from
microplastics is getting more scientific attention as environmental concerns
increases.

2.     Sources
and entry of microplastic in riverine ecosystem

Plastic is made up
of different polymers including Polyethylene (PE), Polyvinyl chloride (PVC),
Polypropylene (PP), Polystyrene (PS), Polymethyl methacrylate (PMMA), Phenol-formaldehyde
(Bakelite), Polyhexamethylene, Nylon
(Nithin, B., & Goel, S., 2017). Wastewater treatment plants (WWTPs),
tourism, fishing activities, goods shipping, municipal sewage discharges into
rivers and harbors are potential sources of microplastic pollution (Sutherland et al., 2011; Norén, 2007;
Claessens et al., 2011; Zubris et al., 2005).Although information on
riverine ecosystem is so far unavailable, effluents from plastic manufacturing
industries may be another source. Actual data about riverine ecosystem is still
scarce. In general, sources of microplastic is generally fall into two
categories either by breakdown of larger plastic objects (secondary MP) or
direct use as resin pellets and using microbeads of plastics in cosmetics and
personal care products (primary MP)
(Thompson et al., 2004; Fendall and Sewell, 2009; Browne et al., 2010, 2011). Domestic
discharges, effluents from industries and wastewater treatment plants are
contributing to plastic pollution that cannot be ignored (Browne et al., 2011).

2.1.        
Primary
microplastics

Plastics
of microscopic size are defined as primary microplastics. These plastics are generally
intentionally used in facial cleansers, scrubbers, shampoos, toothpastes and
cosmetics (Zitko and Hanlon, 1991), or in air-blasting processes for
removal of rust and scaling (Gregory, 1996), in
addition these primary microplastics also used in pharmaceuticals as carriers
of drugs (Patel et al., 2009). Under elaborated definitions of a
microplastic, resin pellets (raw materials for manufacturing of plastics which
size ranges from 2mm to 5mm in diameter) can also come in the category of primary
microplastics (Andrady, 2011; Costa et al., 2010).

The use of microplastic “scrubbers” in hand
washes and facial cleansers, have replaced by some other ingredients like
almonds, oatmeal and pumice (Derraik, 2002; Fendall and Sewell,
2009).The use within cosmetics
like cleansers containing microbeads of plastics has extremely increased (Fendall and Sewell, 2009; Zitko and
Hanlon, 1991).Microbeads used in
cosmetics may vary in size, structure and complexity(Fendall and Sewell, 2009). Different
scientists found that polyethylene and polypropylene pellets with size
of less than 5 mm and polystyrene spheres with size of less than 2 mm are used in different
personal care products and cosmetic goods. These primary microplastics when
come to rivers acts as vectors for the contamination of heavy metals including
Mercury, Cadmium, etc. (Derraik,
2002; Gregory, 1996).

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