Plastic pollution: A focus on freshwater biodiversity

Abstract

Plastics are dominant pollutants in freshwater ecosystems worldwide. Scientific studies that investigated the interaction between plastics and freshwater biodiversity are incipient, especially if compared to the marine realm. In this review, we provide a brief overview of plastic pollution in freshwater ecosystems around the world. We found evidence of plastic ingestion by 206 freshwater species, from invertebrates to mammals, in natural or semi-natural ecosystems. In addition, we reported other consequences of synthetic polymers in freshwater ecosystems—including, for instance, the entanglement of animals of different groups (e.g., birds). The problem of plastic pollution is complex and will need coordinated actions, such as recycling programs, correct disposal, stringent legislation, regular inspection, replacement of synthetic polymers with other materials, and ecological restoration. Current information indicates that the situation in freshwater ecosystems may be as detrimental as the pollution found in the ocean, although highly underappreciated.

Supplementary Information

The online version of this article (10.1007/s13280-020-01496-5) contains supplementary material, which is available to authorized users.

Introduction

The scientific discovery of the first type of plastic occurred more than a century ago. Currently, the production of different polymers reaches more than 300 000 000 tons each year (Plastics Europe 2020). Several plastic materials can be re-used or recycled, but many others must be discarded after the use. Either way, if there is little or no control over production and disposal chains—including consistent recycling policies—plastic materials may be incorrectly discarded and reach aquatic ecosystems (e.g., Eriksen et al. 2014; Chae and An 2017; Lebreton et al. 2017; Giarrizzo et al. 2019).

Much concern has been raised about plastic pollution in the ocean (Cressey 2016), but this pollutant has increasingly threatened freshwater ecosystems (Fig. 1). Lebreton et al. (2017) showed that rivers on the planet contribute with the input of synthetic polymers to the ocean. Numerous studies (e.g., Ballent et al. 2016; Fischer et al. 2016; Ebere et al. 2019; Gonçalves et al. 2020) have also shown the presence of plastics in rivers, sediment, and areas associated to inland waters. This pollution is likely to have numerous consequences for freshwater biodiversity, environments, and ecosystem services. For instance, several fish species in rivers and other inland environments around the world have records of plastic ingestion by one or more individuals (e.g., Andrade et al. 2019; Urbanski et al. 2020). This is worrying because fish is an important feeding resource for several aquatic and terrestrial organisms, so they may act as vectors mobilizing and transferring plastic materials across food webs. Another concern is the entanglement of animals (e.g., freshwater turtles, birds) in fishing nets and other plastic residuals (Ryan 2018; Azevedo-Santos et al. in press). Other types of interactions have also emerged (e.g., Blettler and Wantzen 2019), including effects on aquatic algae and plants in laboratory conditions (e.g., van Weert et al. 2019; Wu et al. 2019). However, the consequences of plastics in freshwaters remain poorly known, basically because few studies have addressed the issue on these ecosystems (Blettler et al. 2018).

Fig. 1.

Examples of plastic pollution in freshwaters ecosystems of South America: a Rocha River (Amazon basin), after crossing urban areas in Cochabamba, Bolivia; b Man removing plastics (e.g., bottles) from Rocha River for recycling; c) polymer pollution in an urban river (Argentina); d plastics accumulated in the margin of the middle Paraná River (Isla Puente, Argentina); e plastic fragments (micro, meso and macro) collected with ichthyoplankton nets in the Paraíba do Sul River basin (Brazil); f remains of fishing nets on the littoral zone of a Brazilian reservoir, after a drawdown event

In this review, we briefly present information about plastic pollution in freshwater ecosystems. We also gathered reports on the interactions between these synthetic polymers and freshwater algae, plants and animals from laboratorial to natural conditions. Lastly, we provide guidance to reduce plastic pollution in freshwater ecosystems.

Plastics in freshwater ecosystems

Freshwater ecosystems are the main destination of different types of pollutants released in a watershed, because aquatic environments are naturally located in valleys and lower elevation terrains. Plastics disposed incorrectly (e.g., streets, roads, open landfills) are carried by pluvial waters to waterbodies (e.g., Faure et al. 2015). Direct discards in rivers, lakes, swamps and other freshwater environments are also frequent (e.g., Gasperi et al. 2014). In fact, the direct disposal of garbage and wastes in rivers is an old tradition in urban and rural areas of the world, only constrained by modern legislation. Domestic and industrial sewage may also conduct plastics to waterbodies, especially when products that include small plastic materials in their composition (e.g., cosmetics) are released in effluent systems (Kalčíková et al. 2017a). In rural areas, especially in those subject to intensive agriculture, the incorrect disposal of contaminated plastics such as pesticide packing is common (e.g., Figs. S1 and S2 in Supplementary Material 1). Other vectors may play a role, sometimes causing massive releases of plastic material in the environment (Bruge et al. 2018; Azevedo-Santos et al. in press). Once plastics reach freshwaters, they may, for example, be trapped by instream structures (e.g., river banks, macrophytes, trees, rocks), go with the water current to floodplain areas, or reach the sediment of contiguous sites (Faure et al. 2015; Peng et al. 2018; Weber and Opp 2020). Physical and/or chemical weathering fragment synthetic polymers into smaller particles over time (Li et al. 2018a), increasing the number of particles in the freshwater ecosystem.

Some authors have attempted to assess the quantity of plastics conducted by rivers (e.g., Lebreton et al. 2017), or the presence of these synthetic polymers in freshwater ecosystems (see Eerkes-Medrano et al. 2015 and Cera et al. 2020). Lebreton et al. (2017) reported that lotic ecosystems are responsible for the input of more than 1 000 000 tons of plastics into the marine ecosystems of the planet. Giarrizzo et al. (2019) indicated that the Brazilian Amazon, including its freshwater ecosystems, receives more than 150 000 tons of synthetic polymers in a single year. Currently, plastic pollution has been reported in freshwaters of several countries in different regions of the planet (Cera et al. 2020).

Plastics and freshwater biodiversity

Studies that investigate the interaction between plastics and freshwater biodiversity are incipient when compared to those that investigate the marine realm (Blettler et al. 2018). Most studies investigate the ingestion of plastics by animals, but other interactions have also been examined. Plastic alone may cause physical, toxic and behavioral impacts, but its association with other pollutants may enhance effects. For example, synthetic polymers may interact with antibiotics (Li et al. 2018b) and other compounds and molecules. Wang et al. (2017), in the Beijiang River basin (China), found microplastics associated with different metals, including nickel, cadmium and lead. Other problem, showed in marine environments, is the association of plastics with persistent organic pollutants, the POPs (e.g., Frias et al. 2010), which are harmful to biodiversity (Jones and Voogt 1999).

In this section, based on Methods in Supplementary Material 2, we compiled evidence of plastic ingestion by 206 freshwater species in natural or semi-natural ecosystems (Fig. 2). We also gathered information about other interactions (e.g., entanglement). Here we synthesize the available knowledge about the interactions of plastic with freshwater algae, plants and animals. In a few cases, we used studies from marine ecosystems as a basis for extrapolations.

Fig. 2.

Number of species with records of plastic ingestion in natural or semi-natural freshwater ecosystems of the world (Tables S1 to S6 in Supplementary Material 2)

Algae and plants

The interaction between algae or plants with plastics has been poorly studied, but laboratory experiments show that plastics may cause negative impacts on these organisms (Kalčíková et al. 2017b; Wu et al. 2019). A recent study (Wu et al. 2019) showed that the algae Chlorella pyrenoidosa Chick, 1903, exposed to plastics, decreased its photosynthetic production. In controlled conditions, Kalčíková et al. (2017b) evaluated the consequences of polyethylene “spheres”, commonly found in cosmetics, on Lemna minor Griff, 1851, and found that tiny plastics affect root development. Aquatic algae or plants may absorb small-sized particles, with risk of making plastic available to secondary consumers (e.g., Chae et al. 2018; Mateos-Cárdenas et al. 2019). Field studies are lacking, but algae and plants in natural ecosystems are likely to respond in a similar way.

Crustaceans

Freshwater crustaceans are susceptible to interact with different types of plastic. Some groups, such as Cladocera, Amphipoda and Decapoda, have the potential to ingest plastic particles (Table S1 in Supplementary Material 2). We found reports of plastic ingestion by 9 species of Crustacea, two in natural and semi-natural environments, and others in controlled conditions (Table S1 in Supplementary Material 2). The negative effects of plastic material on crustaceans may be lethal or sublethal (Table 1). For instance, Cui et al. (2017) evaluated in laboratory conditions the consequences of polystyrene on cladocerans, and found effects ranging from decreased survival to changes in the ability to reproduce. It is possible that the mere presence of certain types of plastics in the environment causes sublethal to lethal effects (e.g., Ziajahromi et al. 2017).

Table 1.

Examples of freshwater organisms negatively affected by plastic ingestion in laboratory or natural conditions

Group	Species	Condition	Effects	References
Crustacean	Daphnia magna Straus, 1820	Laboratory	Sublethal and Lethal	Jemec et al. (2016) and Rehse et al. (2016)
Crustacean	Daphnia pulex Leydig, 1860	Laboratory	Sublethal	Liu et al. (2018)
Crustacean	Hyalella azteca (Saussure, 1858)	Laboratory	Lethal and sublethal	Au et al. (2015)
Mollusk	Corbicula fluminea (Müller, 1774)	Laboratory	Sublethal	Guilhermino et al. (2018)
Mollusk	Dreissena polymorpha Pallas, 1771	Laboratory	Sublethal	Magni et al. (2018)
Cnidarian	Hydra attenuata Pallas, 1766	Laboratory	Sublethal	Murphy and Quinn (2018)
Fish	Oreochromis niloticus (Linnaeus, 1758)	Laboratory	Sublethal	Ding et al. (2018)
Fish	Danio rerio (Hamilton, 1822)	Laboratory	Sublethal	Mak et al. (2019) and Qiao et al. (2019)
Amphibian	Alytes obstetricans (Laurenti, 1768)	Laboratory	Lethal	Boyero et al. (2019)
Amphibian	Physalaemus cuvieri Fitzinger, 1826	Laboratory	Sublethal	Araújo et al. (2020) and Araújo and Malafaia (2020)
Mammal	Trichechus inunguis (Natterer, 1883)	Natural	Lethal	Silva and Marmontel (2009)

Entanglement in ghost nets affects freshwater decapod crustaceans, but there is only one study reporting this problem in natural ecosystems. Spirkovski et al. (2019) reported individuals of Potamon fluviatile (Herbst, 1785) and Astacus astacus (Linnaeus, 1758) entangled in ghost nets in a lake in Europe. Based on this evidence, we predict that large-bodied decapods—e.g., families Trichodactylidae and Pseudothelphusidae—may be more vulnerable to entanglement in ghost nets of polyamide or other plastic objects (e.g., ring, bottles).

Other invertebrates

Different groups of invertebrates are able to ingest plastics in laboratory or natural conditions (Table S2 in Supplementary Material 2). In natural conditions, we found reports for six species (Fig. 2), among these Melanoides tuberculata (Müller, 1774) (Table S2), an invasive gastropod widely introduced (Coelho et al. 2018). In laboratory conditions, negative effects caused by the uptake of synthetic polymers have been investigated for insects (especially larval stages), mollusks (bivalves and gastropods), and freshwater cnidarians (e.g., Magni et al. 2018; Murphy and Quinn 2018; Ziajahromi et al. 2018; Scherer et al. 2020). For example, Stanković et al. (2020) concluded that the exposition of Chironomus riparius (Meigen, 1804) to six types of synthetic polymers caused problems in head structures of the individuals. Murphy and Quinn (2018) showed that plastic ingestion by Hydra attenuata Pallas, 1766 affected the feeding of the animals, in addition to causing morphological changes.

Many invertebrates may be frequently exposed to plastic pollution, since numerous species live near the sediment in aquatic environments (Rosenberg and Resh 1993; Moreno and Callisto 2006), where plastic material accumulates, including microplastic (e.g., Castañeda et al. 2014; Horton et al. 2017). Because studies demonstrated that macroinvertebrates are able to ingest plastic (e.g., Hurley et al. 2017), individuals of this group may constitute an important input of plastic material into aquatic food webs.

Many species of Trichoptera build “cases” with fragments of rock, wood and leaves in freshwater ecosystems (Crisci-Bispo et al. 2004). Plastic may be used by these insects to build such cases, as reported by Ehlers et al. (2019) for Lepidostoma basale (Kolenati, 1848). In the same study, authors suggested that the use of plastic fragments may harm immature forms of Trichoptera.

Fishes

Freshwater fishes are the group with most records of plastic ingestion (Table S3 in Supplementary Material 2). It is difficult to provide an exact number, but Azevedo-Santos et al. (2019a) compiled 75 freshwater species that ingested plastics. Current estimates are above 150 species in natural conditions (Fig. 2) and new studies have been published continuously. This increasing trend indicates that plastic ingestion by freshwater fishes is more common than currently reported, emphasizing the need for more research in freshwater ecosystems, as research has been biased toward marine fishes (Azevedo-Santos et al. 2019a). There is evidence of negative effects of plastic ingestion on fishes, but in laboratory conditions. For example, inflammatory processes in the digestive tract of Danio rerio (Hamilton, 1822), the “zebrafish”, were observed after exposure to polystyrene (Jin et al. 2018). The ingestion of polystyrene, as well other types of plastics (i.e., polyamides, polyethylene, polypropylene, polyvinyl chloride), caused injures to the intestine of fishes (Lei et al. 2018). In a study with the marine species Cyprinodon variegatus Lacepède, 1803, Choi et al. (2018, p. 238) concluded that the ingestion of large amounts of polyethylene may cause “(…) gut distension and abnormal swimming behavior (…)”, which in natural conditions may lead to secondary effects (e.g., vulnerability to predation).

In addition to problems related to ingestion, synthetic polymers may adhere to fish gills (Table 2). This impact has been poorly reported, but there are data for 24 species (Table 2). Gills are vital structures for fish (Evans et al. 2005), and plastics—especially small fragments—may clog or harm this organ, via obstruction and contamination.

Table 2.

Fish species with plastic particles in gills in different freshwater ecosystems of the world (Methods in Supplementary Material 2)

Fish species	Waterbody	Country (continent)	References
Aequidens tetramerus (Heckel, 1840)	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Bryconops melanurus (Bloch, 1794)	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Carassius cuvieri Temminck & Schlegel, 1846	Han River	South Korea (Asia)	Park et al. (2020)
Carnegiella strigata (Günther, 1864)	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Channa argus (Cantor, 1842)	Han River	South Korea (Asia)	Park et al. (2020)
Copella arnoldi (Regan, 1912)	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Crenicichla cf. regani Ploeg, 1989	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Cyprinus carpio Linnaeus, 1758	Han River and Lijiang River	South Korea and China (Asia)	Park et al. (2020) and Zhang et al. (2020)
Dorosoma cepedianum (Lesueur, 1818)	Reservoirs from Bloomington	USA (North America)	Hurt et al. (2020)
Hemibagrus macropterus Bleeker, 1870	Lijiang River	China (Asia)	Zhang et al. (2020)
Hemigrammus unilineatus (Gill, 1858)	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Hoplias malabaricus (Bloch, 1794)	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Iguanodectes rachovii Regan, 1912	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Laimosemion strigatus (Regan, 1912)	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Lepomis macrochirus Rafinesque, 1819	Han River	South Korea (Asia)	Park et al. (2020)
Mastiglanis cf. asopos Bockmann, 1994	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Megalechis thoracata (Valenciennes, 1840)	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Micropterus salmoides (Lacepède, 1802)	Reservoirs from Bloomington and Han River	USA (North America) and South Korea (Asia)	Hurt et al. (2020); Park et al. (2020)
Nannacara taenia Regan, 1912	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Pimelodella geryi Hoedeman, 1961	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Polycentrus schomburgkii Müller & Troschel, 1849	Guamá River	Brazil (South America)	Ribeiro-Brasil et al. (2020)
Pseudobagrus vachellii (Richardson, 1846)	Lijiang River	China (Asia)	Zhang et al. (2020)
Silurus asotus Linnaeus, 1758	Han River	South Korea (Asia)	Park et al. (2020)
Tachysurus fulvidraco (Richardson, 1846)	Lijiang River	China (Asia)	Zhang et al. (2020)

Entanglement of fish has occurred in plastic rings (Table 3). In addition, polyamide or other synthetic fishing nets, when lost or abandoned in the aquatic environment (i.e., ghost nets), have the potential to impact the ichthyofauna for a long time. Azevedo-Santos et al. (in press) presented several reports of ghost nets trapping fish in Brazilian freshwater environments.

Table 3.

Freshwater groups entangled in possible plastic objects* or plastic objects** in freshwaters ecosystems around the world (Methods in Supplementary Material 3)

Group	Waterbodies	Country	Object	References
Crustacean	Lake Ohrid	Macedonia	Ghost net*	Spirkovski et al. (2019)
Fish	Lake from Guarulhos	Brazil	bottle ring**	A.B. Nobile et al. (unpublished data)
Fish	Lake Ohrid	Macedonia	Ghost net*	Spirkovski et al. (2019)
Fish	Paraná River system	Argentina	Ghost net**	Blettler and Wantzen (2019)
Fish	Upper Paraná River system and unknown waterbodies	Brazil	Ghost net**	Azevedo-Santos et al. (in press)
Reptile	Upper Paraná River system and unknown waterbodies	Brazil	Ghost net**	Azevedo-Santos et al. (in press)
Bird	Different waterbodies	Different countries	Different plastic objects**	Ryan (2018)
Bird	Lake from Campinas	Brazil	Likely plastic bag**	Sazima and D’Angelo (2015)
Bird	Lake Ohrid	Macedonia	Ghost net*	Spirkovski et al. (2019)
Bird	Paraná River system	Argentina	Fishing line**	Blettler and Wantzen (2019)
Bird	Upper Paraná River system	Brazil	Ghost net**	Azevedo-Santos et al. (in press)
Mammal	Amazon basin	Brazil	Ghost net*	Iriarte and Marmontel (2013)

Amphibians

The interaction of plastics with freshwater amphibians has been reported predominantly for immature forms. Plastic ingestion has been reported for 18 freshwater species (Table S4 in Supplementary Material 2), 15 of them ingested particles in natural environment (Fig. 2). Laboratory studies have revealed negative consequences on individuals exposed to plastic. Araújo et al. (2020, p. 17) concluded that plastic may “(…) cause external morphological, mutagenic and cytotoxic changes (…)” in tadpoles of Physalaemus cuvieri Fitzinger, 1826.

Laboratorial studies have shown that microplastic may adhere to the gill of amphibians (Hu et al. 2016), but there is no evidence available for natural environments. Considering that it has been reported for wild fishes (see Fishes subsection), and that it was observed in laboratory conditions for tadpoles (see Hu et al. 2016), it must disturb amphibians in natural ecosystems as well.

Entanglement of large freshwater amphibians—especially by ghost nets and smaller fragments—may also be problem. However, this is another gap in the literature.

Reptiles

There are several reports of impacts for reptiles, but they are restricted to marine environments. For example, ingestion of plastic fragments has been reported in more than one continent and for different species of marine reptiles (Schuyler et al. 2014; Nelms et al. 2016). Such interaction may occur in freshwater environments as well, considering that reptiles (e.g., caimans, turtles, snakes, lizards) are found in numerous freshwater ecosystems of the world. Moreover, many freshwater reptiles feed on fish (e.g., Vogt and Guzman 1988; Schmid and Giarrizzo 2019), the group with the best evidence on plastic ingestion among all freshwater animals (Fig. 2). Reptiles, therefore, may ingest plastic directly and indirectly, as birds, mammals and other animals that feed on fish.

Ghost nets are an important threat, despite the scarcity of scientific reports in freshwaters (Table 3). In contrast, entanglement of reptiles has been recorded more often in marine environments (Duncan et al. 2017). Because fishing is a common activity in rivers, reservoirs and other inland aquatic ecosystems (e.g., Castro and Begossi 1995; Okada et al. 2011), where the incorrect disposal of nets is frequent (Fig. 1f), entanglement by ghost nets of nylon (i.e., polyamides) must be a frequent problem.

Birds

Freshwater birds have been threatened by plastic pollution (e.g., Gil-Delgado et al 2017). Individuals may ingest plastic directly or indirectly (Reynolds and Ryan 2018). We found records for 21 freshwater species (Fig. 2), one classified as Near Threatened (Table S5 in Supplementary Material 2). The main consequences of ingestion, based on reports for marine species (e.g., Pierce et al. 2004), is the obstruction of the digestive tract, with risk of starvation. Experimental studies are incipient, and research has focused on physical aspects of the material ingested, such as size, weight, number of fibers, color and shape. In this sense, the effects of plastic ingestion on bird physiology and behavior is considerably underestimated.

Birds are also vulnerable to entanglement in plastic objects (Table 3), as reported for many freshwater species (Ryan 2018). Entanglement may cause sublethal to lethal effects (e.g., Blettler and Wantzen 2019), but, in some cases, birds can escape with minor consequences (Sazima and D’Angelo 2015).

An underestimated problem is the construction of nest with synthetic polymers (see Fig. 2 in Blettler and Wantzen 2019). This behavior makes freshwater birds and their offspring highly vulnerable to contamination, ingestion and entanglement (Blettler and Wantzen 2019).

Mammals

Many freshwater mammals are currently threatened by human activities (Veron et al. 2008), and these animals interact negatively with plastics. For example, there are records of plastic ingestion by Lutra lutra (Linnaeus, 1758), the Eurasian river otter (Smiroldo et al. 2019), and Trichechus inunguis (Natterer, 1883), the Amazonian manatee (Silva and Marmontel 2009; Guterres-Pazin et al. 2012), currently threatened with extinction and categorized as “Vulnerable” (Table S6 in Supplementary Material 2). For the species T. inunguis, Silva and Marmontel (2009) reported that the ingestion of a synthetic polymer caused the death of one individual.

Risks of entanglement are real, especially by fishing nets (e.g., bycatch and ghost nets). For instance, Mansur et al. (2008) reported the entanglement of the freshwater dolphin Platanista gangetica (Roxburgh, 1801) in fragments of fishing nets in Asia. In the Amazon, Silva and Best (1996) reported a case of entanglement and death of freshwater dolphins, Inia geoffrensis (de Blainville, 1817) and Sotalia fluviatilis Gervais & Deville, 1853. Although events like these are known in freshwater environments (e.g., Silva and Best 1996; Martin et al. 2004), entanglement in “ghost nets” and other plastic objects, as reported in marine ecosystems (see Stelfox et al. 2016 and references therein), needs more attention.

Other problem is that some freshwater mammals may use synthetic polymers to build their holts, as reported for the species Lutra lutra (Linnaeus, 1758) in Europe (Kruuk 2006). This behavior also exposes the animal to the risks of plastic ingestion and entanglement.

Final remarks

Plastic pollution in the oceans is colossal and widely recognized by scientists and society (Derraik 2002; Cressey 2016). Plastic pollution in freshwaters have been less recognized, even though plastics are dominant pollutants in these ecosystems—especially near urban areas. Mounting evidence indicate that plastics interact with freshwater biodiversity, from plants to animals. For example, plastic ingestion by animals has been reported for more than 200 species, ranging from invertebrates to mammals. Many studies, particularly conducted in laboratory conditions, show negative effects (lethal and sublethal) associated with ingestion, but consequences in the wild are still poorly known for many groups. More studies are needed to assess the extent of plastic pollution in river networks and associated environments, and the possible interactions with aquatic organisms. We highlight that plastic pollution in freshwater ecosystems may be as detrimental as in the ocean. Different measures are needed to tackle this problem in all regions of the world, since plastic pollution has affected numerous countries with different degrees of development, for example, East Timor, Finland, Kenya, Norway, Pakistan, Scotland, Switzerland, Tanzania, USA and many others (Blettler et al. 2018; Cera et al. 2020; Döring et al. 2017; Hurley et al. 2017; Lusher et al. 2018; Blair et al. 2019; Sarijan et al. 2019; Shruti et al. 2019; Slootmaekers et al. 2019; Khan et al. 2020; Kuśmierek and Popiołek 2020; Merga et al. 2020; O’Connor et al. 2020).

Society must find ways to reduce and remove existing pollutants—including plastics—from natural and semi-natural ecosystems. The problem is complex and will need implementation or intensification of many actions, for example, recycling programs, correct disposal, stringent legislation, regular inspection and ecological restoration (Fig. 3). These actions, if taken accordingly, will minimize plastic pollution on freshwaters and oceans. Specific policies to regulate the use of plastics are needed, as observed in Rio de Janeiro (Brazil), with the Proposed Law 1691/2015 to ban plastic straws (Supplementary Material 4A), or in Kenya, with the Notice No. 2356 that ban bags of synthetic polymers (Supplementary Material 4B). Focusing on marine ecosystems, the European Parliament approved the Directive (EU) 2019/904 on the banishment of disposable plastics untill 2021 (Supplementary Material 4C). International treaties at the world level are also needed to regulate plastic production, trade and disposal (Kirk and Popattanachai 2018). Concomitantly, we need policies to improve solid waste treatment and selective disposal, since these activities are precarious or absent in under-developed and developing nations. Improvements in infrastructure and technology may also curb plastic inputs (e.g., ecologically adapted storm drains), or help removing material from the environment (Supplementary Material 4D–G). The implementation of more restrictive protected areas, including freshwater protected areas (Azevedo-Santos et al. 2019b), is another form to avoid plastics in ecosystems. As showed for another pollutants (e.g., Lowrance et al. 1984), the maintenance of riparian vegetation may serve as a protective filter against synthetic polymers and, at least theoretically, it may trap meso and macroplastic, which could be manually removed before reaching aquatic ecosystems.

Fig. 3.

Main actions needed to reduce (−) plastic pollution in freshwater ecosystems. All actions are connected (+)

The flow of nanoplastic, on the other hand, is much more difficult to control. It would require, for example, the gradual replacement of traditional plastic by alternative material (e.g., biodegradable compounds such as cassava bags; Supplementary Material 4G), demanding investment on research and production. One important step towards a more responsible use of plastic materials (i.e., consumption and disposal) is through education (e.g., Derraik 2002), and different public and private initiatives should be encouraged.

Supplementary Information

Below is the link to the electronic supplementary material.

Biographies

Valter M. Azevedo-Santos

is Doctor in Biological Sciences (Zoology) at the São Paulo State University (UNESP), Brazil. His research interests include ichthyology and conservation of freshwater biodiversity.

Marcelo F. G. Brito

is Associate Professor at the Universidade Federal de Sergipe, in São Cristóvão. His research interests include fish ecology and aquatic conservation.

Pedro S. Manoel

is Doctor in Biological Sciences (Zoology) at the São Paulo State University (UNESP), Brazil. His research interests involve community ecology, mainly landscape effects on freshwater fish and macroinvertebrate communities and trophic relationships.

Júlia F. Perroca

is Master in Biological Sciences. Her research interests focus on ecology, morphology and reproduction of decapod crustaceans, in marine and freshwater environments.

Jorge Luiz Rodrigues-Filho

is adjunct Professor at the Santa Catarina State University (UDESC), Laguna. His studies focus on aquatic ecology, with special interest on the ecology of fishery resources.

Lucas R. P. Paschoal

is Professor at the Faculdade de Tecnologia de Jaboticabal, Nilo De Stéfani. His research focuses on limnology, biology of crustaceans and mollusks, and bioinvasions in Neotropical reservoirs.

Geslaine R. L. Gonçalves

is a Doctor researcher at Zoology Department in São Paulo State University (UNESP), Institute of Biosciences, Botucatu, Brazil. Her research interests focus on growth, food habits, distribution, symbiotic relationships, reproduction, trophic web (stable isotopic analysis with carbon and nitrogen), microplastics and fatty acids.

Milena R. Wolf

is a Post-doctoral researcher at Universidade Estadual Paulista (Unesp). Research area: Taxonomy, reproduction and conservation of freshwater Decapoda, with focus on endemic and threatened species.

Martín Blettler

is a PhD biologist at the The National Institute of Limnology (INALI). His research interests focus on biodiversity and pollution of freshwater ecosystems.

Marcelo C. Andrade

is a Postdoc researcher at the Federal University of Pará (UFPA), Belém. His research interests focus on the diversity and role of ecological specialization, and he is currently investigating the trophic niche and isotopic analysis with emphasis on functional shifts of communities from rivers impacted by dams.

André B. Nobile

is a partner of Ictiológica Consultoria Ambiental, where he works as an environmental consultant in licensing processes, focusing on the ichthyofauna. He develops research on community structure, ichthyoplankton, reproductive biology, trophic ecology and anthropic impacts on Neotropical freshwater fishes.

Felipe P. Lima

is Doctor in Biological Sciences (Zoology). He is currently a partner of Ictiológica Consultoria Ambiental, Botucatu, and works as consultant in licensing processes, focusing on the ichthyofauna. He develops research on community structure, ichthyoplankton, reproductive biology and trophic ecology of Neotropical freshwater fishes.

Ana M. C. Ruocco

is Doctor in Biological Sciences (Zoology). Her research interests include freshwater ecology, limnology and aquatic communities, mainly aquatic macroinvertebrates.

Carolina V. Silva

is Professor at the Faculdade Eduvale, Avaré. Her research is focused on the ecology of inland aquatic environments, particularly the biology and ecology of the macroinvertebrate community.

Gilmar Perbiche-Neves

is Professor at the Federal University of São Carlos, Department of Hydrobiology. His main interests are limnology, ecology, biogeography and taxonomy, especially freshwater copepods.

Jorge L. Portinho

is Postdoctoral researcher at Department of Ecology, São Paulo State University, Rio Claro. He has investigated the ecology of tropical shallow lakes with emphasis on dormant propagules of aquatic plants, invertebrates and the resilience to these aquatic ecosystems.

Tommaso Giarrizzo

is Professor at the Federal University of Pará, Brazil. His research interests include freshwater and marine ecosystems, and human impacts on water quality and biological integrity.

Marlene S. Arcifa

is Senior Professor at the University of São Paulo, Ribeirão Preto. She is interested on limnology, microcrustaceans, fish and ecological interactions in Neotropical ecosystems.

Fernando M. Pelicice

is Professor at the Federal University of Tocantins (Brazil). His research interests focus on aquatic ecology and conservation, with focus on Neotropical freshwater fishes.