Microplastics
Behavior, Fate, and Remediation
John Pichtel and Mathew Simpson
Lanham • Boulder • New York • London
Published by Bernan Press
An imprint of The Rowman & Littlefield Publishing Group, Inc. 4501 Forbes Boulevard, Suite 200, Lanham, Maryland 20706 www.rowman.com
86-90 Paul Street, London EC2A 4NE
Copyright © 2023 by John Pichtel and Mathew Simpson
All rights reserved. No part of this book may be reproduced in any form or by any electronic or mechanical means, including information storage and retrieval systems, without written permission from the publisher, except by a reviewer who may quote passages in a review. The Rowman & Littlefield Publishing Group, Inc., does not claim copyright on U.S. government information.
British Library Cataloguing in Publication Information Available
Library of Congress Cataloging-in-Publication Data
Names: Pichtel, John, 1957- author. | Simpson, Mathew E., author. Title: Microplastics : behavior, fate, and remediation / John Pichtel and Mathew Simpson.
Description: Lanham : Bernan Press, [2023] | Includes bibliographical references and index.
Identifiers: LCCN 2023003071 (print) | LCCN 2023003072 (ebook) | ISBN 9781636710808 (paperback) | ISBN 9781636710815 (epub)
Subjects: LCSH: Microplastics.
Classification: LCC TD427.P62 P53 2023 (print) | LCC TD427.P62 (ebook) | DDC 363.738—dc23/eng/20230202
LC record available at https://lccn.loc.gov/2023003071
LC ebook record available at https://lccn.loc.gov/2023003072
∞
™ The paper used in this publication meets the minimum requirements of American National Standard for Information Sciences—Permanence of Paper for Printed Library Materials, ANSI/NISO Z39.48-1992.
II: SEPARATION OF MICROPLASTICS
PART III: DECOMPOSITION OF MICROPLASTICS
Preface
The generation of plastic waste worldwide has more than doubled over the past two decades.
Globally, a significant percentage of waste plastic is mismanaged, with a substantial proportion released to terrestrial and freshwater ecosystems, and ultimately the oceans. Focused research has revealed that natural processes such as sunlight, abrasion, microbial action, and other mechanisms can convert large plastic debris to extremely fine fragments, fibers, and films microplastics (MPs).
The concept of microplastics emerged on the radar screen of environmental scientists only in the 1990s; since then, water and land pollution by MPs has emerged as a significant environmental and public health concern. It is now recognized that minute plastic particles are pervasive in the environment from the equator to the poles, from the Himalayas to the deep oceans. MPs are known to sorb an array of organic and inorganic contaminants, and be transported through food chains and occur in our food supply. Research reports have only recently identified the presence of MPs in the blood of adults and in stool samples of infants.
In order to effectively control pollution of the biosphere by MPs, there is an urgent need to formulate efficient technologies for their removal and, ideally, their destruction. In the last five years an enormous compendium of articles has been published on regional and global distribution of MPs, behavior and fate, threats to organisms, and methods of detection and quantification. In 2020 alone, an estimated 12,000 papers were published concerning MPs. Substantially less data, however, exists regarding technologies for effective recovery of MPs from water and sediment. The same can be stated for methods to transform MPs into environmentally benign compounds.
Unit operations at conventional drinking water and wastewater treatment facilities have been documented to capture a substantial percentage of MPs from surface water; in contrast, technologies for MP recovery from sediment are primarily at the pilot scale. Additional research is needed to develop and improve upon techniques for MP recovery from both liquid and solid media.
Knowledge is limited regarding methods for the destruction of MPs; however, an array of chemical, physical, and biological methods are currently under investigation. The degree of success varies substantially, and mechanisms responsible for MP destruction are only partly understood. A number of technologies show promise: at the laboratory scale, several have resulted in conversion of MP particles to water-soluble organic compounds and carbon dioxide. Certain innovative methods have transformed organic by-products into useful products such as fuels. These technologies offer promise for long-term water security and ecological stability, and deserve further attention by scientists.
This book provides a comprehensive overview of the MPs issue with emphasis on removal from water and sediment. In addition, the authors present prospective technologies for the destruction of MPs. Part I of this book provides background relevant to understanding the physicochemical properties and environmental behavior of MPs. Chapters address
• polymer chemical composition including the use of additives;
• description of MP types, both primary and secondary;
• MPs distribution in the biosphere;
• sorption of various contaminants by MPs; and
• detection and quantification of these particles.
It is not the intent of this book to review exhaustively the global distribution of MPs, nor their abilities in adsorbing and transporting environmental contaminants many outstanding publications have already addressed these topics in rich detail. Therefore, only a limited review of the distribution of MPs and their ability to sorb environmental contaminants is presented.
Part II focuses on removal of MPs from water including wastewater, and removal from solid media (sediment). Technologies include those currently in use for treatment of municipal and industrial wastewater, and for recovery of minerals and certain solid waste components. Several innovative approaches are included.
Part III addresses technologies for the destruction of recovered MPs. Most methods are available only at the laboratory or pilot scale; however, some have shown great potential for transforming seemingly recalcitrant plastic particles to simple and innocuous products.
Preface
For the benefit of the reader, all terms shown in italics are defined in the glossary at the end of this book. A list of acronyms is included at the end of the book as well.
John Pichtel Mathew Simpson
Chapter 1
Introduction
BACKGROUND
The term plastic was coined in the seventeenth century to describe a substance that is malleable and could be shaped or re-formed; it originates from the classical Greek work plastikos, defined as “able to be molded into different shapes” (Kaushik 2019). Synthetic plastics have existed since the early twentieth century. The modern-day plastics industry had its origins with the development of the first fully synthetic polymer known as Bakelite in 1907, attributed to Belgian-American chemist Leo Hendrick Baekeland (Chalmin 2019).
Through the course of two world wars, chemical technology has made spectacular advances in the development of new polymer formulations. The rapid progress in this new enterprise set the stage for the mass production of plastics for domestic, commercial, and industrial applications in the 1950s and 1960s.
Plastics comprise a large and diverse assemblage of unique and versatile materials that are now embraced by modern society as indispensable for countless applications. In 1950 the annual global production of plastics was a meager 1.5 million tons (Chalmin 2019). Global plastics manufacture has since increased dramatically to meet ever-growing demands. A few minor downturns occurred in recent decades, for example, during the 1973 oil crisis, the 2007 financial crisis, and the Covid-19 pandemic which began in 2019; regardless, global production of plastics continues to flourish. Current plastic production is approximately 368 million tons worldwide (PlasticsEurope 2020), and it is estimated that 8.3 billion tons of virgin plastics have been manufactured since 1950. According to long-term forecasts based on trends of consumer use and demographics, manufacture and consumption of plastic
1.1
Source: Reproduced with kind permission from the American Chemistry Council.
will expand further (Auta et al. 2017) production is predicted to increase at an annual rate of 4% (PlasticsEurope 2018).
The main market sectors for plastics are packaging (31%), consumer and institutional products (17%), and building and construction (14%). Transportation, electrical/electronic equipment, and industrial machinery each comprise less than 10% of the global market share (Hu et al. 2021; Geyer 2017). About 13% of plastics is for other uses (figure 1.1).
Among various resin types, polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) are the most consumed products. Other important resin types include polyethylene terephthalate (PET), polyurethane (PUR), polyamides (PA), and others (table 1.1) (Hu et al. 2021; PlasticsEurope 2020).
THE PLASTICS WASTE PROBLEM
The desirable properties of synthetic plastics such as being lightweight, durable, and resistant to breakdown make them the favored material for countless applications by domestic, commercial, industrial, military, and other consumers. Unfortunately, however, the myriad advantages and usefulness of plastics have given rise to a throw-away mentality in modern society. The majority of consumer plastic products are designed to be disposable after a single use or have only a short usage life; such products are typically disposed within 12 months following manufacture (Koelmans 2014). Other plastics are designed for extended use for products such as water pipes, electric cables, and household commodities (Hassanpour and Unnisa 2017).
Figure
Market Sectors for Plastics Worldwide
Table 1.1
Common Applications of Plastics by Resin Type
Polymer Type
Acrylonitrile butadiene styrene
Low-density polyethylene
High-density polyethylene
Polycarbonate/ acrylonitrile butadiene styrene
Abbreviation Applications
ABS Cases for computer monitors, printers and keyboards, drainage pipe
LDPE
Supermarket bags, food packaging film, bottles, drinking straws, fishing nets, outdoor furniture, house siding, floor tiles
HDPE Detergent bottles, milk jugs, toys, plastic crates, irrigation and drainage pipes, wire insulation
PC/ABS Automobile interior and exterior parts, mobile phone bodies
Polypropylene PP
Yogurt containers, bottle caps, drinking straws, medicine bottles, car batteries, car bumpers, disposable syringes, appliances, carpet backings, rope, fishing nets
Polystyrene PS Food containers, tableware, disposable plates and cups
Expanded polystyrene
EPS Packaging foam, disposable cups, building materials (insulation)
Polyvinyl chloride PVC Plumbing, electrical conduits, shower curtains, raincoats, bottles, window frames, gutters, garden hoses, flooring
Polyurethane
Polyethylene terephthalate
PUR Tires, gaskets, bumpers, refrigerator insulation, sponges, furniture cushioning, life jackets, surface coatings, insulation, paints, packing
PET Soft-drink bottles, processed meat packages, microwavable packaging, pillow and sleeping bag filling, textile fibers, tubes, pipes, insulation molding
Polyamides (Nylon 6,6) PA
Fibers, toothbrush bristles, fishing line, food packaging, inks, clothing, parachute fabrics, rainwear, cellophane
Polycarbonate PC Compact discs, eyeglass lenses, security windows, street lighting, safety visors, baby bottles
Polytetrafluoroethylene PTFE Industrial applications such as specialized chemical paints, electronics and bearings. Nonstick kitchen saucepans and frying pans
Polyvinylidene chloride (Saran®)
PVDC Food packaging
The unique physical and chemical characteristics that polymers possess are responsible for plastic wastes persisting for long periods in both aquatic and terrestrial ecosystems (Habib et al. 2020). The vast majority of synthetic polymers are only slowly degradable, whether by biological or physical/ chemical processes. Due to personal lifestyles, the resilience of polymers,
1
and inadequate or improper waste management, land and waterways worldwide have received staggering volumes of plastic waste. Of the billions of tons of plastics manufactured since the 1950s, almost 80% have been either disposed in landfills or pollute the natural environment (Geyer et al. 2017) (figure 1.2). Lebreton and Andrady (2019) calculated that between 60 and 99 million metric tons of mismanaged plastic waste were produced globally in a single year, and estimated that this figure could triple to 155–265 Mt y 1 by 2060. The combination of demand for single-use plastic products and improper management of plastics worldwide has resulted in approximately 7.5 billion metric tons of cumulative plastic waste generated up to 2021 (Recycle Coach 2022).
Floating on the surfaces of the world’s oceans is an estimated 5 trillion plastic items, weighing 227,000 metric tons (Eriksen et al. 2014); current activities may be adding as much as 11 million metric tons of total plastics annually (Jambeck et al. 2015). About one-third of plastic waste is mismanaged, which accelerates losses to oceans (Ballerini et al. 2018). An estimated 80% of marine plastic debris originates from terrestrial sources (Jambeck et al. 2015; Mani et al. 2015; Wagner et al. 2014). The major activities responsible include littering, illegal dumping, cargo shipping, harbor and fishery operations, and discharge from wastewater treatment plants (Claessens et al. 2011; Habib et al. 2020; Xu et al. 2021). Freshwater bodies such as rivers and other drainages are also contaminated with substantial loads of
Figure 1.2 Pollution by Plastics: (a) Beach in northern UK and (b) Drainage Ditch in Asia
Source: Figure 1.2a: Photo by Andy Waddington, Camus Daraich / CC BY-SA 2.0 (Wikipedia) https://commons.wikimedia.org/wiki/File:Sea_washed_plastic_debris,_Camus _Daraich_ _geograph.org.uk_-_1188625.jpg. Figure 1.2b: https://commons.wikimedia.org /wiki/File:India_ _Sights_%26_Culture_-_garbage-filled_canal_(2832914746).jpg
improperly managed plastics, much of which eventually enters the oceans (Driedger et al. 2015). The largest inputs of plastic waste to the oceans originate from the coastlines of Asia (primarily China and India) and the United States (Lebreton and Andrady 2019; Jambeck et al. 2015). With rising production and consumption of plastics, and with limited regulatory oversight and control in many countries, plastic litter is anticipated to continue to accumulate in marine, freshwater, and terrestrial ecosystems.
The majority of published research which address the environmental threats posed by plastics focus on oceans (Thompson et al. 2009), where waste plastics tend to accumulate (Barnes et al. 2009; Ryan et al. 2009; Ryan 2015). The earliest reports of floating plastic in the ocean appeared in the scientific literature in the early 1970s (Carpenter and Smith 1972; Carpenter et al. 1972). In the Sargasso Sea, Carpenter and Smith (1972) estimated an average concentration of 3,500 plastic pieces km–2 over a distance of 1300 km.
One of the most notorious revelations involving marine pollution by plastics was the discovery of massive “garbage patches,” or gyres, in several of the world’s oceans. The best known is the Great Pacific Garbage Patch located in the North Pacific. In recent years researchers have discovered four more giant patches of concentrated marine debris in the South Pacific Ocean, the North Atlantic, South Atlantic, and the Indian Ocean. Recent research indicates that these patches are growing (Lebreton et al. 2018). The Great Pacific Garbage Patch is believed to have increased tenfold each decade since 1945 (Maser 2014). Plastic debris can circulate in these gyres for years, posing significant risks to marine biota.
By the 1960s, scientists were reporting that northern fur seals ( Callorhinus ursinus ) were becoming entangled in netting and other articles in the Bering Sea (Fowler 1987). At about the same time, researchers discovered that seabirds were ingesting plastic litter (Ryan 2015; Kenyon and Kridler 1969). Plastic was identified in the digestive tracts of prions ( Pachyptila spp.) in New Zealand (Harper and Fowler 1987), and plastic particles were found in stomachs of Leach ’ s storm petrels ( Oceanodroma leucorhoa ) from Newfoundland, Canada (Rothstein et al. 1973). Atlantic puffins ( Fratercula arctica ) were collected from 1969 to 1971 and elastic threads were detected in their stomachs (Berland 1971; Parslow and Jefferies 1972), and plastic particles (mostly PE) were detected in great shearwaters ( Puffinus gravis ) in the south Atlantic Ocean (Randall et al. 1983). Many other types of plastics from bottle caps, plastic sheets, and toys have been found in bird gizzards (Harper and Fowler 1987). Following these early investigations, scientists came to recognize the extensive presence of microplastics (MPs) in marine habitats and their adverse effect on marine life.
MANAGEMENT OF PLASTIC WASTE
Of all municipal waste generated worldwide, approximately 12% is plastic (World Bank 2022). In the United States, plastics generation has grown from 8.2% of waste in 1990 to 12.2% in 2018. Total plastic waste generation was 35.7 million tons in 2018 (US EPA 2021).
The issue of plastics pollution is best addressed proactively, that is, during the consumer decision-making process. In other words, a decline in plastics demand should ultimately be followed by reduced production. Once plastic products are purchased and used, however, a comprehensive plastics separation and recycling program and infrastructure is necessary for effective management. Unfortunately, with few exceptions, the rate of plastics recycling is low in both developed and developing nations worldwide only a small proportion of plastic waste (9%) is recycled (Brooks et al. 2018). The recycling rate of plastic waste in the United States is 8.7% (US EPA 2021) and 53% is landfilled (Luo et al. 2021). In Europe plastics recycling ranges between 26% and 52% (PlasticsEurope 2020) and 31% is landfilled (Luo et al. 2021; Paço et al., 2017).
A number of practical obstacles to plastics recycling exist. First, recycling plastics is more expensive than using raw petroleum feedstock. There is about a 20% increase in manufacturing costs associated with relying upon recycled plastics as compared to costs for utilizing virgin feedstock (Crawford and Quinn 2017). In many less-developed nations, suitable infrastructure is not available for effective waste collection, transport, and management, including recycling and disposal. Furthermore, in many countries there may be little incentive to recycle if the perception exists that landfill space is inexhaustible (and, ideally, far from home). This is compounded by lack of public education about waste generation and recycling.
Another reason for low plastic recycling rates is that different resin types tend to be incompatible in new products; in other words, if recovered HDPE is mixed with PVC, the resulting new product will lack many desired physical properties. Separation of resin types for recycling by the consumer is desirable but not common. The presence of different additives in various plastic products adds to the difficulty of producing a uniform new product.
Lastly, a typical recyclable plastic product can be recycled only about three times. The repeated melting and remolding of the plastic results in loss of mechanical properties: flexibility decreases and the plastic becomes brittle and discolors. With the loss of mechanical properties, the plastic can no longer be applied to its original use and is discarded (Crawford and Quinn 2017).
Only a modest proportion of plastic waste is incinerated. This is partly a consequence of public opposition due to odor generation, and the presence
Introduction
of potentially toxic compounds in gaseous emissions and ash. When certain plastic materials burn they release hazardous organic compounds such as polychlorinated dibenzodioxins (“dioxins”) and polychlorinated dibenzofurans (“furans”); both are associated with serious human health impacts.
If current plastic production and waste management trends continue, an estimated 13 billion tons of plastic waste will occur in landfills or in the natural environment by 2050 (Geyer et al. 2017).
While the problem of plastic wastes on land and in the oceans has received attention from governments and citizens over several decades, only recently have smaller plastic fragments, termed microplastics, emerged as a pollutant of concern (Sharma and Chatterjee 2017).
MICROPLASTICS
Pollution caused by MPs is considered more widespread and hazardous compared with larger litter because of its vastly greater quantities and fine particle sizes (Hahladakis et al. 2018). It is not certain when the term microplastics was first proposed to describe the smallest plastic fragments occurring in ecosystems and in organisms. This term was used by Ryan and Moloney (1990) during research activities at South African beaches. Thompson et al. (2004) used it when describing the extent of contamination of plastic fragments in seawater and coasts of the North Atlantic Ocean. MP size was not defined in these early reports, however.
MPs are composed of many polymer types which correspond to common end-use markets for plastics. The most common MP resin types are PE, PP, and PVC. These are followed by PET, PS, and PA (Andrady et al. 2011; Guo et al. 2019; Alimba and Faggio 2019; Hidalgo-Ruz et al. 2012; Hu et al. 2021). The quantities of plastic waste produced from different polymers is shown in figure 1.3.
MPs are documented polluting oceans, rivers, lakes, and agricultural land (Duis and Coors 2016; Eerkes-Medrano et al. 2015; Van Cauwenberghe et al. 2015), and even occur in the atmosphere in measurable quantities (Chen et al. 2020). MPs in near-shore areas originate mostly from the mainland via wastewater effluent, runoff, rivers, and even air flow. Ships and offshore platforms are sources of MPs to the deep oceans. MPs have been detected at all latitudes and even in polar regions (Mishra et al. 2021). As many as 5.25 trillion plastic particles are estimated to contaminate the global sea surface (Eriksen et al. 2014). Nearly 10% of the total mass of the Great Pacific Garbage Patch is calculated to be composed of MPs. According to Lebreton et al. (2018), over 90% of the small plastic pieces floating on the surface of the gyre (1.1–3.6 trillion pieces) are MPs. A large volume of marine MPs also occurs
Figure 1.3 Proportion of Different Polymer Types in Plastic Wastes
Source: Data from Geyer, Jambeck, Law Sci. Adv. 2017; 3: e1700782. Distributed under CC BY-NC 4.0 License.
in sediment (Koelmans et al. 2017; Woodall et al. 2014). The extent of MPs contamination of freshwater is considered to be as severe as that in oceans (Wagner et al. 2014). MPs are widely detected in inland lakes and estuaries (Driedger et al. 2015). (The distribution of MPs in marine and freshwater environments is presented in chapter 4.)
Size Ranges of MPs
The number of scientific papers that address MP pollution has increased markedly in recent years. Disagreement exists, however, as to the exact size range of MPs, and several definitions have been proffered to categorize them. Particle size is a dominant characteristic as regards determining environmental behavior and fate of MPs (Song et al. 2019; He et al. 2018; Tong et al. 2020; Wang et al. 2021). Finer-sized particles possess a greater surface area compared with larger particles and are thus expected to be more reactive with mineral and organic materials, including living tissue, occurring in the local environment. Bioaccumulation and toxic effects to organisms may also be size-dependent (Kim et al. 2020; Lei et al. 2018; Sendra et al. 2019; Wang et al. 2021). There is general agreement that plastic items larger than 5 mm (originating from the definition provided by Arthur et al. [2009]) be termed macroplastics (figure 1.4).
