With the growing global population and lifestyle changes, human generates vast amounts of plastic waste. Dependency on plastic goods is inevitable today, mainly due to their lightweight, durability, and lower production costs. In 1950 the world produced only 2 million tons of plastic; since then, annual production has increased nearly 200-fold, reaching 367 million tons in 2020, and by the year 2025, this amount is expected to increase around 600 million tons and projected to exceed 2000 million tons by 2050 (PlasticsEurope, 2021). Recent studies suggested the total amount of plastic produced since its invention could be 8.3 billion tons (Geyer et al., 2017). Plastics have become the primary marine pollutants contributing to about 80% of global marine debris. Numerous studies estimated that 8 million tons of plastic items annually enter in the sea. The total amount of plastic waste is projected to increase from 50 million tons in 2015 to 150 million tons by 2025 (Jambeck et al., 2015). The majority of the plastic litter available in aquatic resources is in the form of microplastic (Eriksen et al., 2014). Plastics are broken up into small particles of different shapes (fiber, fragments, pellet, film) and sizes (less than 5 mm in length), known as microplastics. Because of their universal existence, MPs are a global concern, affecting aquatic (freshwater and marine), terrestrial, and distant arctic habitats, consequently influencing numerous lifeforms (Gurjar et al., 2021a). Microplastic (MP) pollution is found in salt, air/dust, fresh and marine water, coastal beaches, bottom sediments, fish and shellfish, and filter-feeder invertebrates. Much attention to MP pollution is given because they are detected in human-related foods such as seafood, honey, beer, milk, table salts, etc. MP has substantial adverse impacts on human health, aquatic organisms, and the global economy.

Source of microplastics

Land-based sources of MPs waste contributed nearly 80% of the total plastic waste in marine environments. Industrial, domestic and coastal activities are the primary paths for entering the plastic items in the marine ecosystem (Derraik, 2002). The creation of plastic items from the industrial feedstock, leaking microbeads and plastic powders from air-blasting practices (Claessens et al., 2011). Commercial fishing activities, domestic wastes, aqua industries, and coastal tourism are further sources of microplastic contamination in the marine habitat. Therefore, marine resources are mainly polluted by plastics that enter the coastal waters through wind, rivers, canals, wastewater discharge, and careless handling of fishing gear (Moore, 2008). As with Abandoned, Lost, or otherwise Discarded Fishing Gear (ALDFG), due to severe weather conditions such as storms, cyclones, and accidents also contribute to vast quantities of debris in marine environments.

Classification of microplastics:

Based on production, MP was categorized into two types such as primary microplastic and secondary microplastic (Andrady, 2011).

Primary microplastic

Primary microplastic is plastic materials that designed or purposefully engineered and produced in sizes ranging from a few µm to 5 mm in length are found in products like toothpaste, face wash, face scrub, body scrub, cleansers, other personal care products, and pre-production pellets and industrial abrasives (Arthur et al., 2009). The entry route of primary MP into the environment mainly depends on their applications: microplastic particles from cosmetic products generally enter through wastewater, while primary microplastic used for raw materials for various products may enter into the environment through accidental loss during transportation and transshipment or through waste runoff from the various processing plants. When plastic items are too small to be retained by wastewater treatment plants, they enter the oceans directly or indirectly pass through rivers and streams that subsequently enter to the oceans.

Secondary microplastic

Secondary microplastic is generated from the degradation of larger plastic items into tiny pieces. Major sources of secondary MP include domestic waste, industrial manufacture, debris from disposed car tires, and paint flakes. These are generated by the breakdown and enduring of larger plastic materials due to weathering, ultraviolet radiation, mechanical forces, oxidative and other wear and tear processes (Arthur et al., 2009). Secondary microplastic is generated from many potential sources and can account for a number of the fragments, films, and fibers observed in the environment.

MPs in aquatic ecosystem 

Inland ecosystems can act as receivers, sinks, and transporter of plastic pollution. Rainfall is a significant driver of environmental MP pollution to inland surface waters. The aquatic environment is affected by plastic pollution due to terrestrial runoff, industrial waste, domestic and laundry waste through rivers, or direct discharge. Human activities in the coastal zone, including fishing, tourism, and marine industry, are also important sources of MP pollution in marine environments. Marine snow (e.g., the continuous settling of mostly organic particles from upper regions of the water column) is an important mechanism that can transport MP from the ocean surface to deep pelagic and mesopelagic zones and may also enhance their bioavailability to marine biota inhabiting benthic habitats (Fig 1). MPs in the ocean can absorb and release toxic substances that are ingested by marine biota (Smith et al., 2018). Globally, numerous studies have observed the availability of microplastics in the GI tracts of commercially important fishes and shellfishes (Gurjar et al., 2021b; 2022).

Acknowledging the facts, horrifying pictures of aquatic animals impacted by the MP particles trigger global awareness and concern adequately. The ingestion of MP items may reduce the food consumption and fitness of the organism. They can also block the intestinal tract and injure gill tissues. Recent studies show that additives such as phthalates, PBDEs, BPA, nonylphenol, and antioxidants can leach out from plastic materials or micro-rubber into the aquatic environment (Amelia et al., 2021), which poses serious health issues (endocrine-disrupting, DNA damage, toxicity, gene alteration) to aquatic animals (Chen et al., 2019). MP can provide a possible pathway for the transfer of absorbed contaminants into the tissue of aquatic organisms, causing a health risk (Fig 2).