Plastic Pollution and Marine Conservation: Approaches to Protect Biodiversity and Marine Life

Plastic Pollution and Marine Conservation: Approaches to Protect Biodiversity and Marine Life provides comprehensive knowledge on the consequences of plastic waste in marine environments at different levels, ranging from ecological and biological, to social, economic and political. The book synthesizes historical information, gaps in current knowledge, and recent discoveries by illustrating the main stages that made plastics a global issue for ocean ecosystems and their wildlife. Written by international experts on marine pollution, marine biology, and management of environmental resources, this book explores the main topics of marine plastic pollution such as input quantification, polluting sources, ultimate fate, ecological consequences, and more.

This an important resource for a wide audience, including marine conservationists, environmental managers, decision-makers, NGOs, private companies, and activists working to combat plastics in our seas and oceans.

• Illustrates the evolution of plastics, from revolutionary materials to global environmental emergency
• Discusses marine plastic pollution with scientific rigor and easy language that is supported by graphics and tables
• Led by a team of editors with expertise in biology, pollution, conservation and policies of marine wildlife, biodiversity and ecosystems

• Language: English
• Publisher: Academic Press
• Release date: Mar 2, 2022
• ISBN: 9780128224878

Book preview

Plastic Pollution and Marine Conservation

Approaches to Protect Biodiversity and Marine Life

Edited by

Giuseppe Bonanno

Department of Agriculture, Food and Environment, University of Catania, Catania, Italy

Department of Biological, Geological and Environmental Sciences, University of Catania, Catania, Italy

Martina Orlando-Bonaca

Marine Biology Station Piran, National Institute of Biology, Piran, Slovenia

Table of Contents

Cover image

Title page

Copyright

List of contributors

Preface

1. Marine plastics: what’s wrong with them?

Abstract

References

2. Microplastics in seawater and sediments—distribution and transport

Abstract

2.1 Introduction

2.2 Microplastics distribution in seawater of the Mediterranean Sea

2.3 Microplastic distribution in subtidal sediments of the Mediterranean Sea

2.4 Types of microplastics in seawater and sediments of the Mediterranean Sea

2.5 Transport of microplastics in marine environment

2.6 Conclusions and perspectives

Acknowledgments

References

3. Fate, transport, and impact of microplastics on planktonic organisms

Abstract

References

4. Plastic impact on marine benthic organisms and food webs

Abstract

4.1 Introduction

4.2 Current knowledge on plastic pollution on marine benthic organisms

4.3 Knowledge gaps and conclusions

Acknowledgments

References

5. Plastic impact on sharks and rays

Abstract

5.1 Marine environment and plastic pollution: a short introduction

5.2 Ghost nets, entanglement and plastic ingestion

5.3 General considerations, future perspectives, best practices, and citizen science

5.4 Acknowledgments

References

6. Marine organisms as bioindicators of plastic pollution

Abstract

6.1 Introduction

6.2 Data analysis of available studies

6.3 Selection of bioindicators

6.4 Monitoring approaches

6.5 Knowledge gaps and conclusions

Acknowledgments

References

7. Marine-protected areas and plastic pollution

Abstract

References

8. Microplastics pollution: a thriller with many leading roles and an unknown ending

Abstract

8.1 Introduction

8.2 Marine plastics, the media, and the influence on policy

8.3 General public and citizen science

8.4 Scientific community and industry

8.5 The possible light at the end of the tunnel with an unknown ending

8.6 Conclusion

Acknowledgments

Supplementary Data

References

9. Perspectives on marine plastics

Abstract

References

Index

Copyright

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List of contributors

Alessandro Acquavita,     Agenzia Regionale per la Protezione dell’Ambiente del Friuli Venezia Giulia (ARPA FVG), Palmanova, Italy

Carlo Giacomo Avio,     Enrico Mestica Comprehensive Institute, Macerata, Italy

Oliver Bajt,     Marine Biology Station Piran, National Institute of Biology, Piran, Slovenia

Nicola Bettoso,     Agenzia Regionale per la Protezione dell’Ambiente del Friuli Venezia Giulia (ARPA FVG), Palmanova, Italy

Giuseppe Bonanno

Department of Agriculture, Food and Environment, University of Catania, Catania, Italy

Department of Biological, Geological and Environmental Sciences, University of Catania, Catania, Italy

Francesco Cumani,     Agenzia Regionale per la Protezione dell’Ambiente del Friuli Venezia Giulia (ARPA FVG), Palmanova, Italy

Mateja Grego,     Marine Biology Station Piran, National Institute of Biology, Piran, Slovenia

Ernesta Grigalionyte-Bembič,     Marine Biology Station Piran, National Institute of Biology, Piran, Slovenia

Katja Klun,     Marine Biology Station Piran, National Institute of Biology, Piran, Slovenia

Lovrenc Lipej,     Marine Biology Station Piran, National Institute of Biology, Piran, Slovenia

Martina Orlando-Bonaca,     Marine Biology Station Piran, National Institute of Biology, Piran, Slovenia

Valentina Pitacco,     Marine Biology Station Piran, National Institute of Biology, Piran, Slovenia

Ana Rotter,     Marine Biology Station Piran, National Institute of Biology, Piran, Slovenia

Giuseppe Suaria,     CNR-ISMAR Institute of Marine Sciences, National Research Council, Lerici, Italy

Rachel Tiller,     Seafood Technology Department, SINTEF, Trondheim, Norway

Manca Kovač Viršek,     Institute for Water of the Republic of Slovenia, Ljubljana, Slovenia

Preface

Giuseppe Suaria, CNR-ISMAR Institute of Marine Sciences, National Research Council, Lerici, Italy

Almost sixty years after plastic pollution first appeared in the scientific literature much progress has been made, and we now have a much better understanding of what are the main sources and impacts of many synthetic polymers commonly found in the marine environment. Research has shown that a wide range of marine organisms is negatively interacting with plastic litter and for some species, a major proportion of the population has ingested plastic fragments and fibers. Laboratory experiments have also demonstrated wide-ranging harmful effects and global concern is growing about the physical and toxicological harm that ingesting plastic debris might cause to natural populations. Many open questions, however, still remain to be addressed and today, after a considerable body of research has been published, a clear understanding of the global plastic cycle is still far from being achieved.

It is widely assumed for instance, that most plastic debris derive from land-based sources, although some studies recently suggested that sea-based sources also play an important role. Nevertheless, there is a surprising mismatch between the estimates of the global inputs of plastic from land, and the total amount of plastic floating at sea. Recent studies suggested that backshores and coastal margins, the water column, or deep-sea sediments, can all be accounted for this missing fraction, however, the fluxes and fate of most plastics entering the ocean every year are currently unknown. There is also a debate about whether the volume of plastics measured at sea over the last decades has kept pace with the global growth in plastic production, as no evidence of increase has been found by many authors. In addition, most figures about the longevity of synthetic materials at sea, are still anecdotal, and solid data about the actual degradation rates of plastics in a range of environmental conditions are urgently required. Reliable information is also missing about toxicological impacts and degradation times not only of the most commonly used polymers, but also about some of the most widespread environments of our planet. The deep-sea for instance, or the water column, that are the two largest ecosystems of the world, are greatly understudied, especially if compared to surface, estuarine or coastal waters, despite comprising the majority of marine habitats worldwide.

Altogether, these findings suggest that our understanding of the global plastic cycle is largely incomplete and many of the biological, physical, and geochemical processes that influence the horizontal and vertical displacement of plastics in oceanic environments, still need to be investigated in greater detail. Technological development will likely play a pivotal role in future research on plastic pollution. Improvement in the capabilities of remote sensing, ocean modeling, and deep-sea exploration, together with the development of innovative and low-cost sensors, all have the potential to enormously improve data availability, facilitating in turn, a more holistic understanding of the complex mechanisms involved with the cycling of plastics through natural ecosystems.

At the same time, the harmonization of sampling procedures and analytical protocols is an imperative priority for the coming years of research. Global standardization of reporting procedures will improve the efficacy of large-scale monitoring programs, enhancing the reliability and inter-comparability of long-term data series, allowing, in turn, a more effective evaluation of current and future mitigation measures. By looking at the history of other anthropogenic contaminants (e.g., heavy metals, pesticides, etc.), great efforts have been made by the scientific community to harmonize analytical protocols, thus allowing meaningful conclusions to be drawn. Standardization of data collection has been already the focus of countless workshops and of many large international projects, as well as of many efforts led by international bodies, private associations, and intergovernmental organizations worldwide. So, the road is paved, and it is just to be hoped that these international efforts will greatly accelerate in the coming years, allowing the scientific community to move one step forward in the comprehension of this relatively new environmental issue. The chapters that follow all move in this direction, presenting critical information on the distribution, fate, and transport of plastic litter in the marine environment, placing a special emphasis on the impacts that plastic pollution is having on marine organisms, their food webs, and on marine ecosystems as a whole.

Given future projections in global plastic production and consumption patterns, it seems inevitable that the quantities of plastic waste will keep increasing in the coming years. Nevertheless, the likely trajectories, environmental sinks or accumulation and degradation patterns are much less clear. Further research into the impact, behavior, and residence time of marine plastic litter will help inform stakeholders and policymakers that aim to tackle, probably not one of the most pressing, but surely one of today's most visible environmental problems. What is now clear is that the number of plastic items currently entering the marine environment needs to be drastically reduced. This can be only achieved through bold international regulations, aimed at reducing waste generation, and at promoting reuse and repair of used items, according to those virtuous examples of zero waste policies already implemented by many communities around the world. These principles are key to the implementation of a more circular economy and at the same time, they really have the potential to greatly improve the resource efficiency of our societies.

Scientific research still sits at the basis of knowledge, and thanks to the tireless efforts of many researchers, a broad recognition has been now achieved by the general public, that plastic debris does not belong to the ocean and that the numerous societal benefits that derive from our everyday-use of plastics can be also achieved without emitting plastics into the environment. Marie Skłodowska-Curie once said that "nothing in life is to be feared, it is only to be understood. And now is the time to understand more, so that we may fear less". And so, we should all be confident that with a little hope, scientific progress can really help us navigate the future, ultimately diverting our debauched legacy to more sustainable alternatives, for the entire planet, and all generations to come.

1

Marine plastics: what’s wrong with them?

Giuseppe Bonanno¹,²,    ¹Department of Agriculture, Food and Environment, University of Catania, Catania, Italy,    ²Department of Biological, Geological and Environmental Sciences, University of Catania, Catania, Italy

Abstract

Plastics are materials composed of polymers, defined as repeating chains of molecules that can be easily processed and shaped. Common plastics are obtained from fossil fuels, such as crude oil and natural gas, and are nowadays the main materials of most consumer goods. The many uses of plastics prompted an ever-increasing production that is now abundantly beyond 300 million tons per year. This massive production made plastics ubiquitous in the environment, especially in marine ecosystems that act as the final sink for most land-based plastic litter. Marine plastic pollution is made even worse by microplastics, whose harmful impact affects the geochemistry, biology, and ecology of all oceans and seas. The effects of marine plastic litter are recognized as a global issue, and important signals to fight this phenomenon come from the main stakeholders such as scientific community with intense research, policy-makers with measures to support a circular plastics economy, the third sector trying to improve their green image, as well as ordinary citizens more and more aware of the sea conditions.

Keywords

Polymers; marine litter; microplastics; bioavailability; ecotoxicology; sea biodiversity; food chains; human health; single-use plastics; circular economy

Plastic is a word of Greek origin that means to shape, to mold, because of its nature of malleable and easily adaptable material. The term plastic is today used to refer to a category of materials called polymers, which are made of long and repeating chains of molecules that can be processed and shaped. The word polymer means indeed of many parts, and polymers are abundant in nature, for example, cellulose is a very common natural polymer that makes up the cell walls of plants. Conventional plastics are a class of organic polymers with a high molecular weight, produced from fossil fuels such as crude oil and natural gas, through the initial process of distillation. Upon heating, the organic substance (e.g., oil, gas) releases different hydrocarbon chains according to their vaporization temperatures. Large hydrocarbon molecules (e.g., ethane, propane) are broken down into smaller molecules during a process called cracking. The resulting monomers (e.g., ethylene, propylene) are polymerized, and this process, called polymerization (Fig. 1.1), allows the molecules to join together to form long chains of repeating units [e.g., polyethylene (PE), polypropylene (PP)].

Figure 1.1 Plastics are polymers, a group of materials made of long and repeating chains of molecules.

Plastics are synthetic or semisynthetic organic polymers that were conceived to provide a material that is lightweight, strong, durable, and resistant to decay, and that can be produced and shipped at low cost (Van Eygen et al., 2017). Due to these key features, since the 1960s plastic materials have been an integral part of human everyday life. Over the last century and a half, humans have learned how to make synthetic polymers, sometimes using natural substances like cellulose, but more often using the abundant carbon atoms provided by oil and other fossil fuels. Synthetic polymers are made up of long chains of atoms, arranged in repeating units, generally much longer than those found in nature. It is the length of these chains and the patterns of their arrays that make polymers so light, strong, durable, flexible, and chemically inert. In other words, this is what makes these polymers so plastic. These features make plastics exceptionally competitive materials; as a result, plastics are extensively used in several sectors and hence their production has been ever increasing in the last decades (PlasticsEurope, 2019).

The term plastics refers to a wide range of synthetic polymeric materials that are designed to meet very different needs of thousands of end products. These plastics include polyethylene terephthalate (PET or PETE), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), polypropylene (PP), or polystyrene (PS). Raw plastics can be combined with organic and inorganic additives to improve their physical properties, to extend the life of plastic materials. Additives such as plasticizers, pigments, stabilizers, and lubricants increase the structural and impact strength of plastics, improve the scratch resistance of the material, provide brightness and color, and reduce plate-out. Thousands of types of plastics are produced today; some of the main types and their uses include: PP (packaging, textiles), PE (packaging, plastic bags), PS (single-use cutlery), PVC (packaging, construction), poly(methyl methacrylate) (PMMA; lenses, cases), nylon (clothing, electronics), polyvinyl acetate (glue), polyurethane (foams, sealants, wheels), acrylonitrile butadiene styrene (Lego), and PET (water bottles, clothing) (Fig. 1.2). These plastics are made of different polymers, whose most common forms are PE, PP, PVC, and PS (Derraik, 2002; Barnes et al., 2009; Aliabad et al., 2019).

Figure 1.2 Plastic water bottles are made of PET, one of the most common commercial plastics.

Plastics can be divided into three main categories: (1) thermoplastics, which can be melted, shaped, and resolidified repeatedly; (2) thermosets, hard plastics that cannot be remelted and reshaped because they form irreversible chemical bonds between polymers; and (3) elastomers, soft elastic plastics. As an estimate of the most common plastic forms today, about seven types of commodity thermoplastics account for roughly 85% of the total plastic available in the markets globally. The density of a plastic depends on the mass of the atoms in the molecule and how the molecules are arranged in space. For example, the density of PE ranges between 0.92 and 0.97; LDPE contains polymers that are linear and repeatedly branching, whereas HDPE is made up of polymers that are unbranched and more tightly packed. Although plastics with densities greater than water, such as PVC, PS, and polyester, are expected to sink through the water column, low-density plastics have also been found in bottom sediments (Ballent et al., 2016). The increase in density, which may allow the bottom accumulation of plastics such as PE and PP, can be attributed to (1) the presence of mineral fillers, (2) adsorption of clay minerals to the surfaces of plastic particles, (3) fecal express following ingestion by organisms, and (4) biofouling (Corcoran, 2015; Zalasiewicz et al., 2016).

Since their introduction, synthetic polymers have met an increasing demand and an expanding market thanks to their wide range of uses. Features such as durability, malleability, low-cost, versatility, and impermeability give plastic materials superior properties compared to traditional materials but, at the same time, have raised environmental concerns because of the persistence of plastics in the environment (Andrady, 2015; Worm et al., 2017; Hale et al., 2020). Due to its durability, the lifespan of plastics is estimated to be hundreds to thousands of years (Wang et al., 2016). In 2014, UNEP announced concern over the threat of widespread plastic waste to marine life. However, it is undeniable that plastics are critical to modern life. Plastics made possible the development of computers, cell phones, and most of the lifesaving advances of modern medicine. Lightweight and good for insulation, plastics help save fossil fuels used in heating and in transportation. Perhaps most importantly, inexpensive plastics increased the standard of living and made material abundance more readily available. Without plastics many possessions that we take for granted could be out of reach for all but the richest people. Replacing natural materials with plastics has made many of our possessions cheaper, lighter, safer, and stronger. The use of plastics has increased 25-fold over the past 40 years (Sutherland et al., 2016) and, driven by public and industrial demands, worldwide production of plastics is still increasing, with current annual production >380 million tons (De Souza Machado et al., 2018).

Natural plastics, such as shellac and latex, were first used to create coverings and insulators during the first half of 1800s. Celluloid was the first artificial plastic, whose manufacturing process was developed in 1869 by the Hyatt brothers. Celluloid was then introduced in Europe in the mid-1870s and was used for numerous products, including billiard balls and false teeth, and it led to the use of cellulose nitrate in making photographic film (Finkelstein, 2008). The first synthetic plastic, Bakelite, was invented by Leo Baekeland in 1909 and was the first plastic resistant to chemical reactions that could be easily molded into different sizes and shapes. Bakelite was followed in the 1930s by the invention of PE, PP, PVC, PS, and PMMA. Although commercially developed in the 1930s and 1940s, the large-scale production of these synthetic organic polymers, derived from fossil hydrocarbons, only really began in the 1950s, but has since rapidly grown to outstrip the production of all other synthetic materials except those in the construction sector (Geyer et al., 2017). Synthetic plastic materials boosted the increase in plastics production and reinforced the relationship between plastics and fossil fuel industries (Brydson, 1999).

Plastics have been reported as a problem in the marine environment since the 1970s (Carpenter and Smith, 1972; Colton et al., 1974). The reputation of plastics fell further in the 1980s as concerns about waste increased. Plastics became a special target mainly because numerous plastic products are disposal and plastic lasts for hundreds of years in the environment. However, only in the last decade has the issue of plastic pollution in marine habitats been identified as a global emergency (Vegter et al., 2014; Perkins, 2015). Studies on small plastic litter in the sea before the 21st century are generally inadequate, and even the term microplastics has not been named until 2004 (Wu et al., 2021). The lines of research into marine microplastics have varied in the last two decades. Early studies (2012 and before) focused on the occurrence and accumulation of microplastics in the sea. These results showed worrying and ever-increasing levels of marine microplastics; therefore, many studies began investigating also the consequences associated with marine plastic pollution. At first, these studies focused on the physiochemical properties of microplastics, and new analytical methods were devised for lab analysis, sampling, and characterization (between 2013 and 2016). In the following years (since 2017 and onwards), the research has investigated mainly the possible harmful effects of microplastics on marine biota and humans. The ecotoxicity of microplastics to marine organisms is still a critical issue for current studies, and the potential uptake of microplastics by humans through food chain is of even more urgent concern.

Plastics were thought to be the greatest threat posed to the marine environment until the discovery of microplastics (Fig. 1.3). Plastics are generally divided into macroplastics and microplastics, the latter term first coined by Thompson et al. (2004). Microplastic particles are a very heterogeneous group differing in size, color, shape, density, and chemical composition. Microplastics were described as a collective debris of tiny or even microscopic plastic mass whose size is <5 mm (Amaral-Zettler et al., 2015; Kershaw, 2015; Lebreton et al., 2017), although several authors proposed different range-sizes such as <10 mm (Graham, Thompson, 2009), <2 mm (Ryan et al., 2009), and <1 mm (Claessens et al., 2011). Barboza et al. (2019) further divided microplastics into large microplastics (1 mm ≤ range size < 5 mm), and smaller microplastics (1 µm ≤ range size < 1 mm). Another classification aims to differentiate microplastics that were manufactured to the current size from those microplastics that were degraded to reach the current size. Microplastics can be indeed classified into primary microplastics, which are plastic particles already manufactured with that microscopic size (e.g., often found in cosmetic and medical products), and secondary microplastics, namely plastic particles resulting from the physical, biological, or chemical degradation of larger plastic materials (Ryan et al., 2009; Duis and Coors, 2016; Hermabessiere et al., 2017). Microplastics may degrade to even smaller particles called nanoplastics whose size is <100 nm.

Figure 1.3 Microplastics pose great threats to marine ecosystems and their biota.

Plastics enter the marine environment via dumping or poor waste management and can originate from a variety of sectors such as construction, households, packaging, and coastal tourism (Li et al., 2016; Siegfried et al., 2017). For example, plastic consumption in households includes the use of plastic bags, single-use plastics, plastic containers, and plastic furniture, and also microplastics in cosmetics and microfibers from textiles products and toothpaste. The majority of marine litter consists of packaging (Fig. 1.4) and small pieces of unidentifiable plastics or PS (Chen, 2015), and primarily originates from land-based sources (UN Environment, 2017). These include general public litter, pollution from industry, harbors, and unprotected landfills and dumps located near the coast or waterways (Galgani et al., 2015). Marine-based sources of plastic pollution have also attracted attention. Marine litter originating from marine-based sources includes commercial fishing, recreational boaters, and offshore oil and gas platforms (Thevenon and Sousa, 2017). The pollution is mainly due to the so-called ghost nets such as lost or discarded fishing gear but also to lost cargo and the discharge of waste during normal shipboard operations (Alpizar et al., 2020). About 80% of plastic leakage into the oceans comes from developing middle-income Asian countries, including China, Indonesia, Philippines, Vietnam, and Sri Lanka (Jambeck et al., 2015), where collection and recovery systems are not adequately equipped to handle the huge amounts of waste (Ellen MacArthur Foundation, 2016). Rivers are a major transport pathway for marine plastics, from which an estimated 1.15–2.41 million tons of plastic waste reach the sea yearly (Lebreton et al., 2017; Schmidt et al., 2017).

Figure 1.4 Most marine litter consists of single-use plastics like food packaging.

One of the main factors contributing to the persistence of plastic debris is its resistance to degradation. In the natural environment, the degradation of plastics occurs when the properties of a polymer are compromised as a result of chemical, mechanical, or biological processes. Specifically, plastic products undergo photooxidative, thermooxidative, and hydrolytic degradation, which, combined with mechanical weathering, promote embrittlement by reducing the molecular weight of the polymer (Andrady, 2011). The result of embrittlement is the creation of microplastics. The main chemical process that affects plastics in the natural environment is photodegradation, which occurs during the reaction of ultraviolet (UV) radiation with groups in the molecular structure of the plastic or its added compounds. The resultant polymer chain breakage enables generated free radicals to bind with oxygen in a process called photooxidation (Singh and Sharma, 2008). Photooxidation reduces the molecular mass of the polymer and causes embrittlement and discoloration of the material. Embrittled plastics are prone to mechanical stress because the material has reduced strength and flexibility. Embrittlement and fracture have significant implications for the dispersal of plastics because smaller particles are transported more easily by water and air. Photodegradation is not concern for the plastic debris already in the sea because the marine conditions of temperature and salinity are not favorable for the photodegradative processes but on land, plastics undergo a much faster process of photodegradation (Moore, 2008).

Another important chemical process affecting the integrity of a plastic is thermal degradation, where molecules deteriorate through molecular scission when overheated. In the natural environment, overheating mainly results from exposure of the plastic material to UV radiation. In contrast to the process of photodegradation, the reactions during thermal degradation occur throughout the particle rather than at the surface only. Thermal degradation can result in color changes, crazing, decreased ductility, and eventual embrittlement. Marine plastic litter breaks up into smaller pieces when exposed to UV B radiation in sunlight, oxidative properties of the atmosphere, and hydrolytic properties of seawater (Moore, 2008). Additional chemical processes affecting polymer stability include ozone-induced degradation and mechanochemical degradation (Singh and Sharma, 2008). The mechanical degradation of plastics refers to the mechanical weathering that occurs in the natural environment, where plastic particles are impacted by sand grains, rock fragments, shells, rigid organic debris, or other plastic fragments. The ideal places for these processes are shorelines, where plastic debris is transported by waves and wind across beach surfaces (Corcoran et al., 2009). The surface textures are also the sites of oxidative weathering products, thus implying that mechanical and chemical processes work together for the degradation-induced embrittlement of plastic debris.

Biological degradation is another major type of plastics degradation. Plastics are generally resistant to biodegradation because polymers are too large to breach the cellular membranes of microbes (Shah et al., 2008). Instead, biodegradation is started either by a mechanical or chemical process, or by biodeterioration, which involves the colonization of organisms within and on the surfaces of plastics (Lucas et al., 2008). The growth and activities of these organisms depend on environmental conditions and on the properties of the polymer, such aspects as crystallinity, molecular weight, functional groups, and additives. Microorganisms can penetrate plastic surfaces by releasing active chemicals or organic acids that contribute to chemical biodeterioration. This allows water to intrude the polymer structure, which leads to hydrolysis and depolymerization. Once depolymerization has occurred, atoms from within the plastic material are assimilated into the cells of the microorganisms, thus providing the energy required for growth and reproduction. In turn, the original plastic product becomes more degraded over time.

There are several natural biodegradable polymers, that is, cellulose and chitin. Synthetic plastics, however, including those that are most commonly produced (PE, PP, PS, and PMMA), are not considered biodegradable in the natural environment. The production of non-natural biodegradable plastics has increased in the past years, although these materials have been used in the medical industry for quite some time (e.g., sutures, drug delivery) (Corcoran et al., 2017). Unfortunately, biodegradable plastics tend to break down only under particular environmental conditions (e.g., temperature, light, types of microbes, scale of composting), which when not met results in burial and preservation. As most plastics are age resistant and only minimally degrade biologically, they stay in the ocean for long periods of time and can travel large distances (STAP, 2011).

The essentially nonbiodegradable nature of plastics, in combination with their light weight, makes them persistent in the sea and easily transportable by water currents. The majority of commonly used plastics are indeed not biodegradable, although they physically break into smaller particles in the marine environment, and enter the food chain (Setälä et al., 2016; Auta et al., 2017). Biodegradability is difficult to achieve and fosters a continued use of plastic, instead of an actual consumption decrease, while a toxic-free production is paramount for a sustainable recycling of plastic (Leslie et al., 2016). Even highly industrialized EU Member States face difficulties in implementing a circular economy for plastic waste (Van Eygen et al., 2018), thus raising the question on how applicable this goal is at global level. Moreover, special focus should be brought on issues of environmental justice, such as legal and illegal waste trade (Brooks et al., 2018). Hence, the development of innovative management measures of plastic waste, as well as the progressive switch toward the production and use of biodegradable/compostable (bio)plastics, is being considered as potential strategies to mitigate the impact of plastic pollution. However, oil-derived synthetic plastics have been produced and accumulating in the environment for several decades, and there are still knowledge gaps about their rates of biodegradation in terrestrial and especially in marine ecosystems (Raddadi and Fava, 2019).

Considering the very low biodegradability of plastics in the environment, there are ever-increasing public concerns about potentially huge accumulation and pollution that could persist for centuries. Since it is clear that plastics have a valuable place in our lives, some scientists are attempting to make plastics safer and more sustainable. Some innovators are developing bioplastics, which are made from plant crops instead of fossil fuels, to create substances that are more eco-friendly than conventional plastics. Other researchers are working to make plastics that are really biodegradable. Bioplastics, which can be bio-based and/or biodegradable, are promising to address many environmental concerns. Bio-based plastics are made from biomass (e.g., cellulose, starch, lignin, and many others): some of them are able to degrade into natural harmless substances, whereas others require special conditions. The global production of bioplastics has grown constantly over the past years; however, bioplastics still account for a very small share of the market (European Bioplastic, 2020).

Although commercially developed in the 1930s and 1940s, large-scale production of synthetic organic polymers, derived from fossil hydrocarbons, only really began in the 1950s, but has since dramatically grown to outstrip the production of most synthetic materials (Waters et al., 2016). Considering the enormous production rates of plastics, one cannot deny their potential role as a stratigraphic indicator of human irrevocable impact on Earth’s stratigraphic record. This is further emphasized by the global accumulation of plastics that hugely outweighs the mass of the current human population on Earth (Zalasiewicz et al., 2016). The development of the plastics industry has made it possible to satisfy the material needs of the world growing population, but it should be considered that the production of conventional plastics production is based on fossil fuels. As a consequence of the innumerable uses of plastics, the production of plastic materials has been constantly growing and is expected to double in the next 20 years (World Economic Forum, 2016; Gu et al., 2017).

World production has greatly increased since the early 1950s to nowadays moving, on a yearly basis, from 1.5 million metric tons (Mt) in 1950 to 311 million Mt in 2014 (PlasticsEurope, 2015), 335 in 2017 (PlasticsEurope, 2017), and to 356 in 2018 of which 64.4 million Mt (c. 18%) were produced in Europe (PlasticsEurope, 2018). China alone accounts for 28% of global plastic resin production (PlasticsEurope, 2016). The largest source of plastics production is packaging, stimulated by the widespread commercial use of disposable containers. Between 2002 and 2014, packaging accounted for around 45% of all polymer resin production (Barnes, 2019), followed by building and construction with 19%, and consumer and institutional products with 12% of production. Geyer et al. (2017) assess that of the 8.3 billion tons (Bt) of plastics produced from 1950 to 2015, 5.7 Bt were waste, 4.9 Bt of which were disposed of into landfills or the natural environment, such as oceans and rivers. According to various estimates (Mathalon and Hill, 2014), about 50% of the globally produced plastics is disposed of after a single use. It was estimated that in 2010 about 5–13 million tons (Mt) of these produced plastics entered the ocean, and if there is no change in the current consumption rates, waste management, and recycling systems, about 12,000 Mt of plastic waste might end up in the natural environment by 2050 (Jambeck et al., 2015). Plastic waste is hence an urgent sustainability problem for which radical and urgent solutions are needed.

While the sea might be the ultimate sink of these persistent anthropogenic pollutants, the impact of plastics is on the whole environment from the atmosphere to the soil, to rivers and lakes. As ubiquitous pollutants with ecological disruptive effects, plastics can be considered as a planetary threat (Villarrubia-Gómez et al., 2018). Plastic products enter the aquatic environment mainly through deliberate dumping, careless littering, industrial spillage during transportation and in factories, and discharge from drainage outlets, effluent pipes, and wastewater treatment facilities. Buoyant plastics in aquatic ecosystems will accumulate at or just below the water surface in zones of concentrated rotating currents (e.g., gyres) (Law and Thompson, 2014). In contrast, nonbuoyant plastics with densities greater than water will sink and become intermingled with bottom sediment (Tubau et al., 2015) (Fig. 1.5). The density of plastics may also be increased: (1) anthropogenically, either during manufacturing or by human activities that alter the original form of the material, or (2) naturally, through mineral adsorption, or by the actions of organisms encountering the material in the environment. Once intermingled with sediment, whether in water bodies or on land, plastics have extraordinary potential to become part of the stratigraphic record as a global anthropogenic marker horizon.

Figure 1.5 Marine bottoms act as a sink of marine plastic debris.

The sinking of plastics and their ultimate burial in aquatic environments are also controlled by water turbulence in different depositional zones. Low-energy environments where plastics are expected to accumulate, if their density allows it, include lagoons, sheltered embayments, estuaries, protected inlets, deep offshore zones, and lake centers. Corcoran (2015) reported that microplastic abundances in lake-bottom sediment from Lake Ontario, Canada were greater near the lake center than near the outlet of the Niagara River, where discharge results in a plume that can travel up to 18 km offshore. According to the model of Zalasiewicz et al. (2016), high-density plastics will preferentially accumulate closer to shore, whereas lower-density plastics will be transported offshore by wind, waves, and currents. Along continental slopes, turbidity currents are expected to funnel plastic debris through submarine canyons to the toes of submarine fans. Once deposited, plastics may become buried by overlying sediment or may be bioturbated and mixed with older deposits. Preservation of plastic material is optimized through burial, especially in zones lacking oxygen (Corcoran et al., 2017).

Microplastics in the marine environment can travel vast distances floating in seawater, or sediment to the seabed (UNEP, 2015). The five plastic gyres established throughout the oceans are well documented, particularly the Great Pacific Garbage Patch (Goldstein et al., 2012). Accumulation in these gyres is further worsened because plastics take centuries to degrade (Cole et al., 2011). In addition to floating and stranded plastic debris, the deep sea is possibly the largest and final depocenter of most plastic debris that are not ingested by marine organisms (Pham, 2014; Angiolillo, 2019) but long-term datasets are very limited, making it difficult to determine a clear trend (Maes et al., 2018). In particular, microplastics continuously fragment in the environment, generating smaller and smaller particles over time; this process depends on many factors including the biological, chemical, and physical conditions that the particles encounter. To properly understand the fate and consequences of microplastics in any marine ecosystem, it is essential to be able to measure plastics across all size ranges, and considering as many types of plastic polymers as possible (Rochman et al., 2019; Hale et al., 2020). Physical factors such as surface waves and turbulence of water currents are also considered to be prominent factors driving fragmentation after the loss of structural integrity of the original debris that reached the sea. This process is cyclic and will result in microplastics debris that is clearly classifiable as microplastics (Browne et al., 2007; Magnusson et al., 2016). Other studies have suggested that these microplastics do not stop their fragmentation at near micrometric scales but go on to form nanoplastics (Galgani et al., 2010).

Synthetic textiles (35%), erosion of tires while driving (28%), and city dust (24%) are reported to be the most important routes of microplastics release into the marine environment; marine coatings (3.7%), personal care products (2%), and plastic pellets (0.3%) only account for 6% of the microplastics releases into the world oceans; and road runoff (tires, road markings, and pellets; 66%), wastewater treatment systems (25%), and wind transfer (7%) are assumed to be the main pathways of microplastics to the oceans (Boucher and Friot, 2017). Considering the input of microplastics in marine environments, it is very important to know the fate and subsequent effects of these particles in marine animals. Marine environments have long been a focal point of microplastics pollution (See et al., 2020), and the first studies of microplastics have also focused on their presence in the sea. As microplastics have been detected in almost all seas of the world, whether in densely populated regions or remote areas, they have been considered as a global challenge since 2009 (UNEP, 2009; Thompson, 2015). Further investigations have then revealed the presence of microplastics in the marine environment, and researchers have proposed two pathways for microplastics entering the sea (Ryan et al., 2009), shedding light on the sources of microplastics in the oceans.

There are two pathways through which plastics end up in the sea: land- and marine-based sources, contributing respectively to 80% and 20% of the total debris (Geyer et al., 2017). Research showed that the sources of marine microplastics were from indirect or direct discharge. Indirect discharge of microplastics into the sea mainly refers to microplastics from terrestrial to marine ecosystems. Data have shown that about 80% of the land-based sources of microplastics (including beach litter) would end up in the ocean (Andrady, 2011). Domestic and industrial drainage systems are two major ways for the transport of terrestrial microplastics into the marine environment (Derraik, 2002). Wastewater treatment plants as the gateway to rivers and finally seas are also important point sources of microplastics, though larger plastic particles may be removed (Browne et al., 2011). However, all the plastic particles accumulated in the ocean are not microplastics because the transport process plays a vital role in the formation of microplastics (Browne et al., 2007). On the other hand, marine industries such as fishing, aquaculture, and offshore oil drilling (Fig. 1.6) can contribute to the direct discharge of microplastics. In particular, nylon, polyester, and PP are major constituents in plastic filament lines and nets, which are commonly found in samples of microplastics (Cole et al., 2011). Illegal forms of disposal contribute directly to marine plastic pollution, and include illegal dumping and littering. In developing countries, waste management facilities are not always available, and solid waste is often dumped in large open areas or directly into rivers. Some kinds of waste, for example, plastic bags, are easily carried by wind and rain into waterways, and from there into the sea. The pathway from marine-based sources to marine debris is particularly important for countries with large fishing fleets, especially if those fleets are mostly informal or artisanal and if the country does not have the port facilities for collection of waste.

Figure 1.6 Oil platforms are important marine-based sources of microplastics.

Oil-based plastic products have become indispensable and ubiquitous in modern life