Microplastics pollution studies in India: a recent review of sources, abundances and research perspectives

Purpose: Microplastics (MPs) are ubiquitous, persistent pollutants that are reported in abundance in all environments and biota. This review highlights the identi�cation, distribution and concentration of microplastics in all aquatic environments and biota in the India region which is one of the least studied with only forty-four papers published on microplastics during 2013-2020 in the web of science. Results: The present review focuses on the concentration of microplastics in different aquatic environments such as 3096 items/kg in marine sediments, 106 items/kg in biota, 59 items/L in seawater, 175 items/kg in sea salt, 33.9 items/L in lake water, 336 items/kg in lake sediments, 288 pieces/m 3 in river water, and 328 items/kg in river sediments. Conclusion: Consequently, we studied the distribution and occurrence of pollution from MPs in coastal and freshwater environments such as rivers, lakes and biota. Therefore, we propose extending studies in all the above areas of microplastics knowing that there are many unique aquatic habitats and species that are yet unexplored. For future research, we suggest new methods for sampling MPs in all marine ecosystems and biota. Assessing research in each of these ways will allow suggesting a microplastic threshold level and devising control initiatives to minimize plastic consumption and its eventual hazard to the aquatic ecosystem. Moreover enforcing strict laws, enhancing legal initiatives, well-planned comprehensive waste management policies and spontaneous public engagement are essential to create awareness of marine plastic pollution and reduce the adverse effects of land-based plastics.

found in the Nattika Beach, Kerala Coast, India. The polymer types were PE, PE + PP, PP, PS, and PCU identi ed using FTIR and SEM. [82] reported that concentration of plastic debris concentration of 8.96 kg/m and their distribution of 56.42% in the beach litter along Chennai, East Coast of India. The food wrappers, cups, bottle and caps, thermocol/styrofoam, and food wrappers identi ed. [83] reported that concentration of microplastic concentration of 72.03 MPs/100g and their distribution of 56.32% and 300μm-1mm in size found in the beaches of Puducherry, India. The polymer types were polyurethane, HDPE, polypropylene, polystyrene, and LDPE identi ed using Raman spectroscopy. [85] reported that microplastic concentration of 403 pieces and their distribution of 60.8 % and >1.01-200mm in size found in the Rameswaram beach, GoM, Southeast coast of India. The polymer types were polyethylene, polystyrene, nylon, and polyvinyl chloride identi ed using FTIR spectroscopy. [86] reported that plastic debris concentration of 505 pieces in the Nallathanni Island, SE of India. The polymer types were polystyrene, polyethylene, polycarbonate, polyvinyl chloride, and nylon identi ed using FTIR spectroscopy.
[88] reported that concentration of plastic debris concentration of 3.24 kg and their distribution of 44.89% in the Marina beach, Chennai, India. [91] reported that plastic debris concentration of 7.49 g and their distribution of 55.33% and 1-5 mm in size found in the beaches in Mumbai, India. The polymer type was plastic identi ed. [92] reported that concentration of plastic debris concentration of 3.24 g m -2 and their distribution of 80% and 5-100 mm in size found in the beaches in Mumbai, India. The polymer type was plastic identi ed. [60] examined that presence of microplastic concentrations average of 134.29 items/kg in the sediments, and 19.87 items/L in water, and their distribution of microplastics were 44%, and 58% in sediments, and water respectively. The particle size range of 1-5mm, and 500µm-1mm (in sediment, and water respectively) along the coast of the Tuticorin, Gulf of Mannar (GoM), India. The polymer types were PE, PP, PP-PE, PA, PET, PEST, PVC, PS, RA, and PVA identi ed using FTIR-ATR, SEM, and EDAX.
[65] examined the presence of microplastic concentrations average of 12.75 items/kg in sediments, and 21.60 items/L in seawater, and their distribution of microplastic is 100, and 100 % respectively. The particle size ranges from 1-3 mm, and 0.5-1 mm respectively in the Roche Park, Coast of Tuticorin, Gulf of Mannar, Southeastern of India. The polymer types were PE, PP (Magallana bilineata), PE, PP, polyester, polyamide & paint in sediments, and PE, PP in seawater identi ed using FTIR-ATR analysis. In quantities of plastic debris is highest amount of 8.96 kg/m in marine beach to prove that shoreline and recreational activities are the primary cause of beach debris litter along Chennai, India [82].
[96] reported that microplastic concentration of 277.90 items/kg and their distribution of 49% and 0.01 -3 mm in size found in the Beaches of Puducherry, India. The three polymer types were poly (ethylene; propylene; styrene) identi ed using Celestron Digital Microscope. [97] examined that presence of microplastic concentrations of 0.93/m 3 , and 45.17 /kg (water, and sediments respectively). The particle size range of 35.29 to 5010 μm, and 46.72 to 5024 μm (in water, and sediments respectively) in the Port Blair Bay, Andaman Islands, India. The polymer types were ionomer surlyn, poly etherimide, acrylic (Acryl Fiber), polyphenylene sul de, ethylene vinyl alcohol, acrylonitrile, nylon, ethylene-vinyl acetate, polyisoprene, polyurethane, PVC identi ed using FTIR-ATR. [98] reported that plastic debris concentration of 1029 items/m 2 and their distribution of 96% and > 1 mm in size found in the Vavvaru Island of the Maldives, Indian Ocean. The polymer types were polyethylene, polypropylene and polystyrene, but polyurethane, polyamide, polyvinyl alcohol and polyvinyl chloride identi ed using ATR-FTIR spectroscopy.
[99] examined the presence of microplastic concentrations of 288 pieces/m 3 , 96 pieces/kg, 84.45 pieces/kg in water, sediments, and soil respectively), and their distribution of microplastic is 86.51%. The particle size range of 1-5 mm and 0.3-1 mm in the Netravathi river, India. The polymer types PE, PET, PP, and PVC identi ed using FTIR-ATR. Due to its widespread usage as packaging materials, higher polyethylene abundance is the primarily used plastic raw material in Indian industries [138]. The compared with other rivers, In Portugal's Antua River, microplastics abundance ranged from 13.5 to 52.7 mg/kg in March, and 2.6 to 71.4 mg/kg in October [139], higher than Haihe River [140] and marginally lower than Pearl River [141,142]. [100] examined that MPs concentration ranges from 0.68 to 148.31 ng/g and 11-64 ng/g items/kg and their distribution of 70% and 5 to 10 mm in size found in the riverine sediments of Ganga, India. The polymer types were PET, PE, PP, and PS identi ed using FTIR. This degree of microplastic abundance was found to be smaller than other world rivers. Likewise, plastic debris concentration ranged from 228 to 3760 items/kg in the Rhine river [143], 178-544 items/kg in the Beijiang river [119], and 185-660 items/kg in the Thames river [32] which is less than previous.
The numerical fraction of microplastics in the Ganga was identi ed higher compared to the concentration of microplastic ranges from 0.60-160 items/kg in the Bloukrans river, South Africa [144]. This disparity in the concentration of meso and microplastics in these rivers is due to several factors including pollutant loading, hydrodynamic state and spatial location [145,146]. Depending on these considerations, certain places were observed to have large concentrations of plastics relative to others. PET, PE, and PP were the most popular plastic forms in Ganga river sediments, while bres (polyesters) and sheet or lm were the most signi cant morphotypes. Compared to other morphotypes such as lm and beads, microplastic waste highlighting bers was recently emphasised [147].
[76] reported that microplastic concentration of 343 items 50 g −1 d.s. and their distribution of 100% and <5 mm in size found in the southernmost coast of India (Kanyakumari), India. The polymer types were ber and fragment identi ed. [77] examined that presence of microplastic concentrations of 40.7 particles/m 2 , 1.25 particles/m 3 , 22 particles in sediments, water, and sh respectively), and their distribution of microplastic is 96.10%. The particle size range of 0.3-0.6, 0.6-1.18, and 1.18-2.36 mm in the Kerala, Southwest coast of India. The polymer types PE; PP; PA; PS; PET; RY; PUR; alkyd; CE; ABS; PVC; PVFM sediments, PE; PP; alkyd; RY; PS; CE in water, and PE; CE; RY; PL; PP in sh identi ed using FTIR-ATR, FP-XRF. [87] reported that microplastic concentration of 496 items m -2 and their distribution of 91% and <5 mm in size found in the Vembanad Lake, Kerala, India. The polymer types were Polymers; Polypropylene; polyethylene, and polystyrene identi ed using Raman spectra. [89] reported that microplastic concentration of 5500 pellets found in the Goa coast, India. The polymer types were PE and PP identi ed using FTIR-ATR. [148] reported that microplastic concentration of 1200 pellets 2 to 5 mm in size found in the found in the Chennai coast, India. The polymer types were Polyethylene and Polypropylene identi ed using FTIR-ATR. [93] examined the presence of microplastic in sea salt, and their distribution of microplastic is 60%. The particle size of 100 μm in the Tuticorin coastal salt pan stations, Gulf of Mannar, South India. The polymer types PE, PP, CL, and NY identi ed using μ-FT-IR and AFM. MPs were also recently reported from Arctic sea ice, sh, sea birds and sea salts in heavily polluted surface waters. Only a small range of global studies have been carried out on the quantity and distribution of MPs in marine salts [149][150][151][152][153]. [94] reported that microplastic concentration of 72 items/kg and their distribution of 100% and 100 to 500 µm in size found in the sea salt in the Salt of Tuticorin, Southeast Coast of India. The polymer types were polyethylene, polypropylene, polyester, and polyamide identi ed using SEM-EDAX. The study shows that people consume around 216 MPs/year particles through sea salt if the average individual has 5 g daily salt intake.
[95] investigated the MPs concentration of 103 particles kg -1 and their distribution of 80% and 2000 μm and 500 μm in size found in the sea salt in the Mumbai, Indian sea salts, Southeast Coast of India. The polymer types were polyesters, polystyrene, polyamide, polyethylene identi ed using μ-FTIR. Microplastic abundance in sea salts may be due to sea salt being a direct product of coastal water. The amount of MPs in the salt samples tested by this analysis was observed to be smaller than those in China and Spain's sea salts and well salt [154,155]. Low-density MPs may also be transferred from surface soil to deeper soil levels horizontally and vertically through soil fractures as well as by earthworms, collembolan and other species [156][157][158][159]. It may also be affected by airborne pollution [155,160,161]. [101] examined the presence of microplastic concentrations of 309 items/kg, 28 items/km 2 , 5.9 items/L in sediments, and water respectively), and their distribution of microplastic is 80%. The particle size range of -1 to 0.3 mm, 0.3-2 mm in the Veeranam lake, Tamil Nadu, India. The polymer types such as nylon, polyethylene, polystyrene, polypropylene, and polyvinyl chloride identi ed using ATR-FTIR. [102] examined that presence of microplastic concentrations of 5.9 particles/L, 27 items/kg, in water, and sediments respectively), and their distribution of microplastic is 99%. The particle size range of 0.33-2 mm in water, 2 mm in sediments of the red hills lake, India. The polymer types were HDPE, LDPE, PP, and PS identi ed using ATR-FTIR, SEM. The causative factors of these microplastics are primarily attributed to the weathering phase degradation of plastic goods and even from shing nets, as these are the signi cant contributors of microplastics in water and sediments [162][163][164]. A further probable route for microplastic is by dry deposition, by wind transport. The dust generated by, i.e., automotive emissions, tyres [165] from the soil, deposition and dispersion between the atmosphere, the environment and the marine domain may also promote the transportation of microplastic [166], although this requires detailed analysis [167].

Ecotoxicological effects of microplastics on biota
Microplastic particles were found in many aquatic biota, such as shes (Anodontostoma chacunda, Arius arius (11) (50), and shrimps (20), sh (72). Fourteen studies reported the intake of microplastics by aquatic species in India. From these researches, 1895 aquatic organisms were analysed and more than 95% of the species studied were found to be infected by microplastic particles (Table 3).

Microplastics (MPs) in vertebrates
Two primary mechanisms absorb microplastics into vertebrates: predators feed on food already infected with microplastics (through intake or external microplastic), or predators directly absorb microplastics from the water, and sediments. Microplastics in different forms were found in 1470 no. of shes (52 species) in India (Table 3).
[58] examined the presence of microplastic concentrations average of 0.005 items/g in edible tissues, and 0.054 items/g in inedible tissues of shes, and their distribution of microplastic is 11.6% and 88.4% (edible and inedible tissues respectively). The particle size ranges from 115-210 μm, and 136 to 4010 μm (edible and inedible tissues respectively) in the Kerala, India. The polymer types were PE, PP in edible tissues and PE, PP, EPDM, PS in inedible tissues of shes identi ed using ATR-FTIR.
In conditions of particles per organism, larger vertebrates have eaten higher concentrations of microplastics than sh. Highest microplastic abundance values were reported in India's southeast coast [97]. By examining microplastic abundance in sh from different studies in India, we found that microplastics abundance in Indian sh was of the same magnitude as in other countries. For particles per weight, microplastic was identi ed in Istiophorus platypterus showed in the Tuticorin, Southeast coast of India, which had an abundances of 0.0002 MP/g in gut, 1.10 MP/g in body, and 0.11 MP/ individual due to depth about >200m [94]. In terms of depth of locations, microplastic was concentration is 0.2 MP/g in gut, 0.008 MP/g in body, and 3.64 MP/ individual found to be Harpodon nehereus due to depth above 1-3 m. In conditions of particles per weight, microplastic was found to be Piaractus brachypomus showed in the Ramsar, Vembanad Lake, south India, which had 26 % MP intake in sh [62].

Microplastics (MPs) in invertebrates
In the ecological food web, microplastic toxicity has been observed to in uence both the basal food web species and all kinds of species [114]. Indian invertebrate absorption of microplastic particles was studied in bivalves, shrimps, and other benthic species. At present, six studies have analyzed microplastic contamination in invertebrates in India and 508 organisms have been reported to be microplastic polluted (Table 3). Among these species, bivalves are of particular concern since their extensive lter-feeding practices expose them to plastics in the waters they visit [110,168]. The con rmed rate of microplastic ingested by aquatic invertebrates was 58.58%. The microplastic abundance in aquatic invertebrates in India ranged 0.04 to 3.78 and from 0.39 to 7.05 items/g. [58] reported the presence of microplastic is 0.04 items/g (0.39 ± 0.6 items/shrimp) in the foregut and midgut of Fenneropenaeus indices (Shrimp -330). The particle size range from 500 to 1000 µm and 30.9% distributed in Cochin, Kerala, India. The polymer types were poly (amide, ester, ethene, and propylene) identi ed using FTIR. [59] reported the presence of microplastic is 3.78 g and 7.05 items/g (soft tissue and bivalve respectively) in the Perna viridis (90) and Meretrix meretrix (110). The particle size range of <100 μm in the Pondicherry, India. The polymer types were poly (amide, ester, ethene, and propylene) identi ed using Raman spectrum & Fluorescence microscope.

Microplastics (MPs) size in different aquatic environments and biota
A main element affecting the ingestion of microplastic particles is their small size, as many low-trophic species have little potential to turn plastic from food and would feed upon it which is reasonable in size [119,169]. In general, size was also strongly linked to microplastics toxicity [170]. In the 53 reviewed papers, 35 researches recorded the size spectrum ( Table 3) In marine Chennai beach has been size in 5.5-25 mm in beach sediments [73]. The irregular plastic particles are produced mainly from dampening household plastic materials by urban drainage and partly by sea. Previous reports indicate a higher distribution of fragments and bres than other sources in coastal sediments [171][172][173]. Polymer types such as polyethylene, polypropylene, and polystyrene oat on seawater and y long stretches, having been located far from their primary origins [174].

Cleaner sea National Marine Litter Policy in India
India releases 600,000 tonnes of plastic waste annually into the oceans. We need to develop the right clean-up technology to overcome the marine plastic pollution. In order to regulate identify and monitor the source of plastic litter along the India's coastal line the Union Ministry of Earth Sciences took an initiative to clean up the oceans by adopting National Marine Litter Policy along with UN Environment's global 'Clean Seas Campaign' on 2018. This policy is about how do we reuse and recycle plastic for cleaner sea. National marine litter Policy aims in (i) identifying the path of plastics from source to sink and promoting Reduce, Reuse and Recycle (3R's) concept to create awareness (ii) enumerating the plastic litter in marine sediments, water and biota along the Indian coast (iii) to build a monitoring, management and mitigation procedures to overcome the impact of Microplastics to clean up oceans.

Research gap
Main criteria to tackle research gaps pertaining to microplastics in the marine environment.
1. Present a optimal and standardised size description of a microplastic, with additional size speci cations for nano-and mesoplastics 2. Improve and adopt systematic, high-throughput microplastic sampling methodologies to effectively correlate the outcomes from various research areas 3. Establish effective methods to identify tiny microplastics and nanoplastics in water columns and sediments 4. Broaden understanding of the nature and behaviour of microplastics in the water column, together with the consequences of fragmentation and biofouling. 5. Adapt methods to assess microplastic absorption by biota in the food web and extend usage of sentinel organisms (e.g., Fulmars) to detect microplastic abundance in the marine environment.
. Identify the impact of ingested microplastics (leached plastic additives, waterborne pollutants) on marine biota and recognize its transition within the food chain.

Conclusion And Future Recommendations
This is rst time from India this kind of review paper were written in the microplastic pollution in different aquatic environment and biota. In this review 44 papers were collected from Web of Science during 2013-2020, mainly focused on concentration, identi cation, size and distribution of microplastic in different aquatic environment and biota. From previous research it can be concluded that the sampling and detection of MPs in majority of research in the marine environment performed in sediments, biota, and seawater. We have also targeted the freshwater environments such as lakes and rivers in India which has different types and level of MPs pollution and a new 3 dimensional and mathematical modelling analysis is proposed. The level of microplastics is abundant in the areas where activity of industries and residents were placed near to fresh waters. The majority intakes of microplastics were accumulated in gut and gastrointestinal tracts of biota. Furthermore the role of Waste water treatment plants in emitting microplastics into the nearby aquatic environment should to be concentrated and effective steps to be taken to setup tertiary treatment plants in India to reduce the microplastic pollution from WWTPs. Research gaps in establishing the effective techniques in identifying nanoplastics, origin of microplastic sources, transportation through various aquatic environments from land based plastic wastes, absorption of microplastics by biota and their impact in the food web and food chain still has to be focused predominantly in the future studies.
Focused on these reviews, following conclusion can be derived    1  Biota  12  2  Beach sand  17  3  Island  3  4  Riverine  2  5 Marine sediments 4 6 Sea salt 3 7 Lake (water & sediments) 2 8 Sea water 1  Spatial distribution of microplastics in different aquatic environment in India