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Plastics and the Ocean. Группа авторов
Читать онлайн.Название Plastics and the Ocean
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isbn 9781119768418
Автор произведения Группа авторов
Жанр Химия
Издательство John Wiley & Sons Limited
There remained what many considered the most important aspect of plastic pollution, its effect on human health, as papers quantifying the plastics consumed in seafood were becoming common. In 2017, Fred vom Saal and Aly Cohen edited an Oxford University Press Publication titled Integrative Environmental Medicine intended for medical practitioners. Their goal was to mainstream cutting‐ edge concepts that were not taught in traditional medical courses. Sara Mosko, a physician and I contributed a chapter: “The Plastic Age: Worldwide Contamination, Sources of Exposure and Human Health Consequences.” The Key Concepts included this provocative statement: “The list of human health problems that correlate with exposure to chemicals in plastics reads like a catalog of modern Western diseases.” Although correlation is not causation, correlations do merit further investigation. We are now in the phase of plastic pollution research where the dividing line between environmental effects and medical research has been breached and medical researchers are looking seriously at potential human health effects. While at first, concerns about eating fish that had consumed plastic were paramount, we now have ample evidence that exposure through respiration is a greater threat, and that plastics at the nanoscale have invaded consumables of all kinds.
An implication of the dictum that the dose makes the poison is that as the dose of a substance increases, so does its potential toxicity. There are certain substances in plastics that contradict this. I imagine a crowd unable to get through a door when an individual could. Binding to receptors can exhibit a U‐shaped curve where a very low dose given at the right time binds to a receptor and larger doses have less effect until the system is eventually overwhelmed at very high doses. Future ocean plastic research will examine such questions and others as they relate to population‐level effects.
This volume concludes with two chapters on behavior change and legal remedies, which are certainly important in stemming the tide of vagrant plastics invading the ocean and the entire biosphere. However, the economic drivers of plastic pollution are in the ascendant, and until the worldwide growth of infinitely variable plastic products is redirected by a major paradigm shift, scientists will continue to work in a “different” plastic world.
1 Plastics in the Anthropocene
Anthony L. Andrady
Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA
We live in an era where human beings dominate and control most geochemical processes on Earth’s surface, including some aspects of the ocean system. It is impressive that Homo sapiens accounting for a mere 0.01% of the biomass on Earth, can exert such control; the mass of structures built on Earth by man now exceeds the total biomass on the planet (Elhacham et al. 2020). The present epoch of man deserves to be formalized a distinct period, the Anthropocene, within the geological time scale (Crutzen and Stoermer 2000). This era started in the post‐World War II (WWII) years (Steffen et al. 2015; Zalasiewicz et al. 2016) and is ongoing. Plastics, a unique identifier of the Anthropocene, survives as stratigraphic markers in the soil to guide future archeologists exploring our era. Historical origins of plastics, however, can be traced further back in history, perhaps to 1869, when Wesley Hyatt invented nitrocellulose as a potential substitute for elephant ivory that was used to make billiard balls at that time. Even though Wyeth’s celluloid billiard balls were a failure (as some of them exploded on impact), this unique product opened the floodgate for synthetic plastic products in to the consumer world. But, the commodity plastics we are familiar with today, came of age much later when the War effort spurned a rapid expansion of the materials industry in the US with public funding allowing new plastic resin plants to be built to produce vital plastics for the military supply chain.
Postwar years saw the enthusiastic acceptance of plastics by consumers worldwide, thanks mostly to the efforts of industry to promote plastics as a unique “wonder material,” and much was expected of this novel semi‐utopian material that promised a wide range of affordable products. Today, plastics have emerged as the material of choice in a variety of applications ranging from food packaging to spacecraft design. The abundant societal benefits of plastics (Andrady and Neal 2009) are evidenced by the rapid substitution of conventional materials used in packaging, building, transportation, and medicine, with plastics. Plastics have, by now, become indispensable to the modern lifestyle, with their per capita consumption governed generally by the affluence of the country. While the US, Canada, and Japan, for instance, use over 100 kg per capita of plastics annually, India and some countries in Africa or Central Europe, use less than 50 kg per capita (e‐Marketer 2021). To meet this steadily increasing global per capita demand of an average ~46 kg annually, plastic resin production had grown to 359 million metric tons (MMT); 432 MMT inclusive of the polymer used in synthetic textile fibers) in 2019. China accounted for about 30% of the production, and with ~50% of the global resin demand in Asia, the country is well poised to remain as the leading resin manufacturer in the world. The annual global production of plastics in the year 2015 alone, if processed into a thin plastic “cling film,” was estimated to be large enough to wrap the entire earth in plastic wrap (Zalasiewicz et al. 2016).
An estimated (Geyer et al. 2017) 7300 MMT of plastic resin and fiber was manufactured globally from just after WWII until the year 2015. By 2020, this figure rose to 8717 MMT. More than half of this was either PE (~36%) or PP (~21%). In addition, the thermoplastic polyester (e.g., poly(ethylene terephthalate) [PET]) used in beverage bottles, polystyrene (PS) in packaging, and poly(vinyl chloride) (PVC) as a building material, were also produced. Reflecting their high‐volume use, these same 4–5 classes of plastics typically dominate the plastic content in the municipal solid waste stream (MSW), in urban litter, as well as plastic debris in the marine environment. The current discussion is therefore focused on this limited set of plastic types: PE, PP, and PS foam that dominates floating plastic debris in surface waters of the ocean and nylons or polyamide (PA). PET, PS, and PVC, mostly found in the deep sediment. Deep‐sea sediment is the most important sink or repository of waste plastics that enter the ocean every year. While no systematic quantitative assessment is available, there is little doubt that plastics accumulate in the benthic sediment and a recent estimate places it conservatively at about 14 MMT (Barett et al. 2020).
1.1 What Are Plastics?
The term “plastic” is used in common parlance as if it is a single material. But it is, in fact a broad category of materials that include hundreds of different types. Plastics are a sub‐class of an even larger group of materials called the polymers, characterized by their unique long chain‐like molecular architecture, made up of repeating structural units. They tend to be giant molecules with average molecular weights (g/mol) in the range of 105–106 (g/mol). Being a subset of polymers that can be melted and re‐formed into different shapes repeatedly, they are therefore called thermoplastics. The word “plastic” is derived from ‘thermoplastic [See Box 1.1]. Hundreds of chemically distinct types of thermoplastics exist, even though only a few are used in most consumer plastic products.
This is somewhat analogous to the about 95 elemental examples in the group ‘metals’ and their numerous commercially available blends, even though only a few common ones such as copper or aluminum are extensively used. The same is true of plastics, but even within a single type of plastic such as polyethylene (PE)1 several different varieties of resins with different characteristics are available. For instance, the common varieties of PE are low‐density polyethylene (LDPE), high‐density polyethylene (HDPE), medium‐density polyethylene (MDPE), and linear low‐density polyethylene (LLDPE) resins. Each of these varieties includes different grades of that plastic with range of properties despite their identical repeat‐unit chemical structure. For instance, one grade of LDPE (low molecular weight grade) is a soft wax used as a lubricant, while another (ultra‐high molecular weight grade) of PE, is spun into fibers so strong that they are