plastic makes up 80% of the plastic debris released from the terrestrial environment to the oceans (Horton et al. 2017; Law & Thompson 2014). With this growing awareness of the importance of the riverine source of plastic wastes in the marine environment in recent years, several studies have been carried out in various world rivers. These include the Los Angeles River (Moore et al. 2005), Danube (Lechner et al. 2014), Yangtze Estuary (Zhao et al. 2014), Rhine (Mani et al. 2015), Selenga River (Battulga et al. 2019), Beijiang River (Tan et al. 2019), Ciwalengke River (Alam et al. 2019), and others. This chapter discusses the various works done with freshwater MPs across the globe, with a special focus on studies in India.
2.2 The Nature and Production of Microplastics
The Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) (2015) defines plastic as a synthetic, water‐insoluble polymer, generally of petrochemical origin, that can be molded on heating and designed into various shapes to be maintained during use (Arthur et al. 2009; Lassen et al. 2015).
The plastic pollutants encompass a wide range of synthetic polymers, some of which are polyethylene terephthalate, high‐density polyethene, polyvinyl chloride, polyethene, polypropylene, and polystyrene. These present a wide range of different sizes of plastic polymer materials that are present (meter to micrometers) in our surroundings. According to National Oceanic and Atmospheric Administration (NOAA) and the European Chemicals Agency, MPs are small plastic pieces less than five millimeters.
After entering the ecosystems, these plastic particles undergo degradation and fragmentation processes and it becomes difficult to identify and remove them, particularly the smaller size fractions. These particles are water‐insoluble and not easily biodegradable, and are chemically durable over long periods. These MP pollutants easily move long distances through aeolian transport (Gasperi et al. 2018) and water, and accumulate in the environment. Thus, due to the validation of the long‐range transport of plastics via air and water, the misconception of plastics being a local junk or waste as thought of a few decades ago is now being rebuffed, and plastics are now acknowledged as a serious threat to the global environment.
The threat of plastic pollution can be managed early through efficient source identification. In recent years many researchers have reported potential MP sources, fluxes, and sinks of these pollutants using theoretical models (Figure 2.1) across a wide variety of hydrological reservoirs (Alimi et al. 2018; Browne 2015; de Souza Machado et al. 2018; Horton et al. 2017; Horton & Dixon 2018; Nizzetto et al. 2016; Wagner et al. 2014). Extensive risk management and assessment of this emerging contaminant requires a proper and exhaustive understanding and quantification of the sources and emissions pathways across the world, spatially as well as temporally, with a special focus on freshwater sources and fluxes, This will help in the understanding of the sources, fluxes, and sinks, and contribute immensely to a proper estimation of the global budget of plastics input to the oceans, which can be useful for source mitigation schemes and for planning long‐standing monitoring and assessment strategies.
Figure 2.1 Showing the pathways of plastic fluxes across the various hydrological reservoirs, indicated by brown arrows, which represent the fluxes where extensive research is going on. Blue arrows represent plastic fluxes (theoretical) that have yet to be studied in detail
Source: Modified from Windsor et al. 2019.
2.3 Global Ecological Impacts of Plastic Pollution
The harmful effect of plastics on the various life forms and the ecology may be due to various feedback mechanisms (Figure 2.2). While available literature reports mostly physical effects due to exposure to this pollutant on organisms or ecosystem function, chemical effects due to various processes such as adsorption and bioaccumulation of toxic chemicals, and the impacts due to leaching of harmful additives in plastics have not been investigated.
One of the most observed hazardous physical effects of plastic pollution that has been found in various studies is entanglement and external physical damage to larger organisms from plastic items such as fishing nets and rope (Jacobsen et al. 2010). The smaller organisms also face problems such as zooplanktons exposed to MPs, which suffered from antennal and carapace deformities (Ziajahromi et al. 2017). Moreover, due to the similarity in size of these debris with that of the larvae of several organisms and planktons, many aquatic life forms can suffer by ingesting these plastics (Besseling et al. 2014; Boerger et al. 2010; Browne et al. 2008; Kaposi et al. 2014; Tanaka & Takada 2016). Recently, several studies have investigated that the hazardous chemicals can be transported into organisms through various pathways, and these can eventually cause health hazards in humans by reaching through the food chain, which is another concern (Besseling et al. 2017; Browne et al. 2013; Koelmans et al. 2013; Koelmans et al. 2016; Rochman et al. 2015; Tanaka et al. 2013, 2015; Thompson et al. 2009; Van Cauwenberghe & Janssen 2014; Wright & Kelly 2017). A recent study (Wilson et al. 2020) revealed that plastics represent the most diverse habitat for invertebrates in some rivers, which is a sad state of affairs.
Figure 2.2 Ecological effects of plastics (
Source: adapted and modified from Windsor et al. 2019
).
2.4 Socio‐Economic Impacts of Plastic Pollution
Plastic delivers many benefits to society and is responsible for the promotion of a wide range of technological advances which have revolutionized our day‐to‐day lives. However, increasing awareness and available records of potential environmental impacts, at present mostly on the marine world (Thompson 2017), are forcing us to stress upon the potential negative impact on the economy and various industries, such as fishing and tourism. Very scattered and scarce data are available, mostly restricted to local impacts, yet these are indicative of widespread global socio‐economic effects due to plastic pollution. The fishing industry, in particular, is likely to suffer detrimental impacts of plastic pollution due to reducing amount and damaged catches (Thompson 2017); one such study surveyed fishing vessels in Scotland and revealed that 86% of the fishing vessels reported that plastic pollution in the sea resulted in a reduction in fish catches (Mouat et al. 2010). In addition, another serious problem is entanglement reported within marinas and harbors, with 70% of the marinas and harbors that were surveyed reported that they experience various problems due to plastic litter (Mouat et al. 2010).
Contaminated catches may also result in significant economic loss due to the high concentration of plastics in the fish stocks (Foekema et al. 2013; Lusher et al. 2013). Moreover, it may have a detrimental effect on the salability of commercial fishes due to the negative public perception of these contaminated supplies (GESAMP 2016). Another industry likely to be affected is tourism, as public perceptions of esthetically pleasing and clean sites are likely to influence people's choices of places to visit. Tourists visiting the coasts may not have positive feedback about the locations where they found litter, affecting the market value of the place as a tourist destination (Brouwer et al. 2017), and litter on beaches can cause physical injury (Werner et al. 2016). Thus, to boost the tourism sector and for environmental reasons, the local authorities execute cleanliness drives (Mouat et al. 2010). Plastic wastes are causing huge
