Microplastics in Freshwater Systems: A Review on Its Accumulation and Effects on Fishes

Plastic production is escalating tremendously throughout the globe and the reason behind this is its durability and multipurpose utility. But there is a severe scarcity of its management. Tonnes of plastics are dumped into water bodies across the world. These plastics breakdown because of different reasons and results in the plastic debris of size <5mm termed as microplastics (MPs) which are hazardous to aquatic life. They are a potential source of toxins as they offer a large surface area to various chemicals present in the water body when these MPs are ingested by fishes it causes serious health issues leading to mortality of the fishes. Therefore, we comprehensively reviewed the sources of MPs in freshwater systems and its various types and how they get accumulated inside the body of fishes. We found that fishes ingest these particles by mistaken for food or accumulated these particles by consuming from lower trophic organisms. Some of the commonly studied MPs are PE, PS, and PVC, examined from the body of fishes. MPs can cause various ecotoxicological effects on fishes like behavioral change, cytotoxicity, neurotoxicity effects, and liver stress etc. Our review study finds that there is a paucity of information on the accumulation of MPs by freshwater fishes and there are very few studies on its effects also there is a debate whether this accumulation is subjected to the bio-magnification process which ultimately affects human life.


INTRODUCTION
Plastic materials are of vital use, being non-corrosive, durable, non-reactive, lightweight, easy to handle and its cheap manufacturing cost has made it a material of choice.Plastic production continues to accelerate and the reason behind this is the adoption of use and disposes of culture by almost all the developed and developing countries.Annual plastic production has increased from 1.5 million tonnes in the 1950s to 288 million tonnes in 2012 (PlasticsEurope, 2013) with only 9% of plastics being currently recycled in the USA (EPA, 2014).The non-recycled plastic is being disposed off in dump yards, a major proportion of it is thrown as debris in the water bodies including oceans and rivers.It is estimated that 275 million metric tonnes of plastic waste is being generated each year (based on reports from 192 coastal countries, 2010).Due to a variety of physical, chemical and biological factors, these non-recycled plastics in the water bodies, breaks down to form microplastics (MPs).MPs from personal care products are one of the potential sources of direct addition to freshwater streams.Most of the studies have occurred in marine water systems but little data is available on the abundance and distribution of MPs in freshwater systems however MPs pollution is found in estuarine water and freshwater systems (Zhao et al., 2015;Su et al., 2016).Most studied impacts of plastic debris on biota are their physical effects such as entanglement, ingestion and suffocation/asphyxia (Barnes et al., 2009;Ryan et al., 2009;Sigler, 2014).These microplastics are often consumed by fishes via a variety of methods and cause adverse effects leading to mortality, neurotoxicity, cytotoxicity, liver stress, behavioural changes, oxidative stress, genotoxicity etc (Luis et al., 2018).Plastic abundance was found between the stomach, gut, and intestine of the fishes.The objective of this paper is to review the current knowledge of MPs contamination in freshwater and its effects on fishes.Summary of its occurrence and distribution is also discussed along with explored knowledge of its effects on fish health have been presented in this study.Several challenges have been discussed and suggestions are provided for further research work.

MICROPLASTICS Overview-Types & Sources:
At first, the term 'microplastics' was used for the plastic matters in the range of 20µm (Thompson et al., 2004).But later, this range was widened in the range smaller than 5mm (Arthur et al., 2009) and also the upper limit is 1mm (1000µm) stated by (Van Cauwenberghe et al., 2015).However, microplastics (MPs) are commonly defined as plastic particles having the size less than 5mm.(Betts, 2008;Fendall and Sewell, 2009;Hidalgo-Ruz et al., 2012).This study concerns primarily on the presence of MPs in freshwater bodies and its impacts on fishes.Research efforts on the accumulation and impacts in the freshwater system are very much less than the marine and terrestrial systems (Thompson et al., 2009;Wagner et al., 2014).The concentration of MPs is constantly increasing in the aquatic environment due to a tremendous increase in the production of plastics, with a total global production of 335 million tonnes in 2016 (Plastic Europe, 2017).Most of the authors have concluded that the primary sources of MPs are effluents from wastewater treatment plants (WWTPs), sewage sludge, shipping activities, atmospheric fallouts, direct disposal from the public, beach littering and run-offs from agricultural, recreational and urban areas.Although the data is so far unavailable, the runoffs from industrial plastic production sites can be taken as an additional source.The products such as facial scrubs have been identified as a potential source of MPs in water bodies.A study shows that the size range of four personal care and cosmetic product waste were in the range of 63-125µm, 125-250µm, 250-500µm, and 500-2000µm (Browne, 2015).Generally, MPs are classified as primary or secondary on the basis of their production.Primary MPs are the ones having size <5mm and mainly are originated from textiles, medicines, toothpaste, and variety of other personal care products like facial and scrubs (Cole et al., 2011;Browne et al., 2015).The range of primary MPs and its types mainly consists of fragments (Rummel et al., 2016), fibres (Rummel et al., 2016), films and foams (Anderson et al., 2017).Secondary MPs can be originated by the fragmentation of big plastic materials degradation.They are derived from the degradation of larger plastic debris through mechanical forces, thermal degradation, photolysis, thermo-oxidation and bio-degradation processes (Zhao et al., 2015).For example synthetic fibres from washing clothes (Browne et al., 2011).Secondary MPs arising by washing clothes are generally polyester, acrylic, and polyamide which can be more than 100 fibres per litre of effluent (Habib et al., 1998;Browne et al., 2011).

Methods of ingestion of MPs by fishes:
Ingestion is one of the most common factors associated with plastic debris, have been reported by more than 270 taxa (Laist, 1997)   Plastic debris ingestion in fish from different freshwater habitats like rivers, estuaries, and lakes from different locations across the globe was examined by different researchers and was found that a lot of species ingest MPs.The data provided in Table 1 shows the percentage of individuals observed with plastic debris inside the gut i.e., shown as frequency percentage.Among the estuary species the frequency percent was highest in Cathorops agassizzi which were collected from Goina estuary (Brazil) in the year 2011, it had ingested debris percentage of approx 33% which is quite high.Other species like Cathorops spixi and Sciades herbergii showed the frequency equal to 18%.The genus Stellifer had ingested debris frequency percentage between 6 to 9 specifically Stellifer brasilliensis (found lowest among estuary species observed) and Stellifer stellifer had 6.9 and 9.2% of ingested debris frequency respectively.Other species like Eugeress brasilianus, Eucinostomos melanopterus, and Diapterus rhombeus was found with 16.3, 9, 2, 11.4 % of frequency debris respectively.
The reports from the species thriving in Lake Victoria of African continent showed almost static frequency percentage of 20% among the studied species Lates niloticus and Oreochromis niloticus studied quite recently in the year 2016 by (Biginagwa et al., 2016).There was a high frequency of ingested debris among the species of river habitat, so far Haplosternum littorale collected from Pajeu River (Brazil) had a remarkably highest frequency percentage of 83%; It is predicted to be hazardous for humans via food chain, However, it is just a hypothesis actual effects are yet to be analyzed.Other species collected from Brazos River Basin (USA) also showed the high percentage of ingested debris frequency, Leponis megalotis and Lepomis macrochirus were observed with 44 and 45% frequency respectively studied by Peters and Bratton in the year 2016.Sanchez examined Gobio gobio from 7 rivers of France in the year 2014 and found a range of frequency percentage with 9.5 to 4.2%.The overall result shows that the species thriving in the rivers are mostly affected by the MPs contamination.The reason behind this could be because the river is vulnerable to various sewage discharges along with factory wastes so the chance of contamination is highest.According to the hypothesis, the biomagnifications of MPs is likely to be highest through river water species and the consumption of the infected fish with MPs can be hazardous for humans also.

Effects of microplastics on fishes:
The  As MPs act as a sponge and provide surface area for various bio-organic or inorganic toxic substances; the ingestion of these adsorbed toxin containing MPs could be a serious health issue for the fishes.WHO is considering launching a health review in response to a study where MPs were found more than 90% of some of the popular packaged water brands.

Conclusions:
This paper compiled the comprehensive information about the importance of the study of MPs contamination in fresh water along with the ways of accumulation and effects on fishes.In this regard, the following topics were discussed a).Microplastics overview-types and sources, b).Methods of MPs by fishes and c).Effects of MPs on fishes.
From the literature it can be concluded that MPs are a dormant hazard for aquatic organisms and their quantity is increasing day by day, it is the reason behind the several abnormalities in the behaviour and health of fishes.Fishes ingest MPs intentionally and sometimes unintentionally, the MPs get accumulated in the gastrointestinal tract and stomach of biota.PE, PS furthermore PVC is among the most extensively studied MPs obtained from inside the freshwater fishes.The study shows the data on the ingestion of MPs by fishes of different freshwater bodies and also provides graphs to show the effects of these accumulated particles on fishes.
Based on the investigation following conclusions can be drawn: 1.More attention is needed towards freshwater MPs studies.2. Regulate some rules to counter the generation of MPs in water bodies.
3. There should be a ban or monitoring over the production of personal care products containing MPs, as they are one of the primary sources.4. Toxic effects and biomagnifications of MPs through food chains need to be evaluated comprehensively.5. Better understandings of MPs effects on humans.6. Find out techniques to filter out MPs from wastewater in treatment plants, 7. should establish techniques of detection and filtration of MPs from water at a satisfactory level.8. Further studies should be directed towards prevention, awareness, and reduction and counter methods.
from a variety of trophic level(Cole et al., 2011).One of the most affected taxa is fish.Plastic and other debris may be intentionally ingested by fish(Cole et al., 2011;Laist, 1997).Incidental ingestion happens with the ingestion of natural food items(Peters and  Bratton, 2016), or through trophic transfer, when fish consumes prey that has already ingested plastic debris(Cedervall et al., 2012;Mattsson et al., 2015).On the other hand, intentional ingestion occurs when the plastic material is mistaken for food, especially bottom algae and fragment like foods (Ivar do Sul and Costa, 2007).Evidence suggests that intentional ingestion of plastic is most common in fish.For instance, marks left in large plastic debris suggest fish frequently attack and bite plastic items present in the environment(Carson, 2013), and laboratory experiments suggest fish larvae feed preferentially on plastic particles when exposed to both microplastics and natural food(L€onnstedt and Ekl€ov, 2016).The ingested MPs usually get accumulated inside the stomach, gut, intestinal lining of the fishes which we examine to observe whether the ingestion has happened.
effects of MPs contamination on fish health are not yet fully understood.The ingestion of MPs by fishes can get accumulated in their digestive tract which can cause starvation because of the false sensation of satiation or even perforation of the gastrointestinal tract.It may also pass to predators including humans (Ferrel and Nelson, 2013; Seltenrich, 2015; Sharma and Chatterjee, 2017).Internal and digestive enzyme system may get damaged even the reproduction can because of MPs digestion (Talvite et al., 2015; Wright et al., 2013).Examples of studies are listed below.
Fig showing some of the effects of MPs of freshwater fishes.