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[Note: Two asterisks indicate a provisional conclusion that will be expanded into more detailed narrative. Three asterisks indicate an additional topic area, not yet boiled down to a conclusion, that is being prepared for incorporation into the document.]
This document is concerned specifically with the production of plastics materials (generally termed "resins") by chemically combining relatively simple organic feedstock molecules ("monomers") into much longer molecules ("polymers"). Subsequent shaping of the resins through extrusion, molding, or similar physical processes is an important industrial activity in its own right, but its environmental impacts are generally lower in intensity, and that aspect of plastics production is not considered in detail here.
From a strictly environmental perspective, the main business of the resin manufacturing sector is to convert prospective air and water contaminants, often rather toxic or hazardous materials, into prospective solid wastes, generally of a much more benign nature. In addition to taming their hazard levels, the plastics industry plays another role in mitigating the environmental effects of the precursor materials. The monomers are small, chemically active carbon containing molecules that would, if released into the air, turn rapidly through natural processes into the prototypical greenhouse gas (carbon dioxide). Subjected instead to the processes of the resin manufacturers, they are sequestered into a stable form that will, left to themselves, keep their carbon content out of the atmosphere for an extended period (perhaps centuries or millennia in typical landfills). Furthermore, the uses to which plastics are put can mitigate the environmental impacts that would have occurred if the same functions had been served by other materials. For example, plastics are often substituted for heavier materials (requiring more fuel to transport), or for materials whose production requires more energy. The plastics industry gets little enough respect from the general public. An appreciation of these positive aspects of its environmental impact would not be unwarranted.
Counterbalancing these positive results are the usual impacts accompanying virtually any manufacturing process. Since the processes of resin manufacture involve chemical transformations, much of the material in the document in this series concerning the chemical industry is applicable to this discussion. The reader is referred to that document for general background on chemical processes. The following analysis will focus on matters specific to the production of plastic resins.
In addition to impacts from resin manufacture, the plastic industry must also be concerned with certain unique risks associated with its products. Although the polymers themselves are typically of little concern (except as solid wastes, or, in the case of some polymers, when incinerated), certain additives to polymer formulations may pose health risks to consumers, and to the environment.
Environmental impacts and risks
Quantitative impact data
Effects of existing and future regulations on impacts
The distinction between manufacturers of resins from monomers and manufacturers of plastics products from resins is recognized in the NAIC system at the three digit level. Plastics resins manufacturers are classified under the general category of chemical manufacturers, NAICS 325, as the subcategory 325211, "Plastics materials and resins manufacturing". The makers of plastics products from resins are grouped into the three digit NAICS category 326, "Plastics and rubber products manufacturing". The SIC code corresponding to NAICS 325211 is SIC 2821, Plastics Materials, Synthetic and Resins, and Nonvulcanizable Elastomers".
The 1997 Economic Census lists 529 establishments under NAICS 325211. There are several very large resin producers, but also many smaller ones. According to the OECA Sector Notebook on Plastic Resin and Manmade Fiber (which uses data from the 1992 Economic Census), 71 percent of the establishments in the sector have fewer than 100 employees. There has been some consolidation in the industry since these figures appeared, but the sector is by no means completely dominated by large plants, as some sectors dealing with bulk materials are (such as, for example, those commodity chemicals manufacturers who form the backbone of the resin makers' supply chain.) An environmental improvement program targeted toward this sector would be dealing with many smaller establishments along with the giants.
Data from The American Plastics Council (APC) show that, between 1997 and 2001, the area of largest growth for plastics has been in the packaging market, with a compound growth rate of 4.2% per year. This is, of course, the one area in which the mitigating factors associated with plastic's environmental impact, such as its use in products that remain serviceable for the long term (thus displacing more energy intensive materials and sequestering carbon, as mentioned in the beginning of this document) are least applicable. Typical plastic packaging, seldom reused, is solid waste in the making. Other growth areas include buildings and construction, at an average of 3.8% per year. Its growth rate in transportation, where it might be expected to have a beneficial effect on fuel economy, has been less dramatic, at 1.3% per year.
Environmental impacts from resin production depend on the types of monomers involved, and on the processes used in the polymerization reactions. Among the most common types of materials are:
There are a number of other polymers familiar to most consumers, such as the acrylics (available both in sheet form as Plexiglas®, and as common apparel fibers), the fluorocarbon polymers such as Teflon® and Kevlar®, and the thermoset resins, such as polyurethanes and epoxies (these latter types tend to form three dimensional webs rather than long chains, that do not soften when heated). There are also a wide variety of copolymers, formed by various combinations of the different monomer types. In addition, there are engineering polymers with special properties, such as polycarbonate, a reasonable substitute for window glass. And while the list of new polymers is not growing as rapidly as it did during the latter half of the twentieth century, there will undoubtedly be new and newly popular resins appearing from time to time. However, the polymers on the list above account for most of the tonnage, and therefore most of the environmental impact, of the plastics sector, and are likely to remain the dominant contributors for some time to come.
The chemical characteristics sketched above may help shed light on the impacts associated with the production of each of the major polymer types. Some of the impacts are associated with properties of the monomer. For example, vinyl chloride, a gas, is a carcinogen. Fugitive emissions in the workplace must be carefully controlled. Traces of the monomer may exist in the polymer, so PVC is not a good choice for applications that would bring the material into contact with food or drinking water. One of the monomer types involved in polyurethane production, molecules containing isocyanate groups, is also a health hazard. The most commonly used monomer, toluene diisocyanate, is a relatively nonvolatile compound, and is thus of concern as a constituent of solid waste, although release of vapors into the atmosphere from polyurethane production can also affect people in close proximity to the production facility, as well as plant workers.
Other impacts are associated with the production process. Polymerizations can be carried out with only the monomer and polymer, along with lesser quantities of catalysts and other production aids. This is referred to as "bulk polymerization". The typical environmental impact comes from escaped monomer. Alternatively, polymerizations can be carried out in a solvent phase. Not surprisingly, the greatest environmental impact in such cases is often associated with release of the solvent (either to air or wastewater).
In some cases, synthesis of the active monomer from precursor materials is carried out in the same facility that then carries out the polymerization reaction.
*** [more detail relating environmental impacts to properties of materials and production processes]
*** [discuss cellulosic materials -- the production of the "polymer" is done agriculturally, rather than synthetically, but there are significant impacts associated with the production processes for, e. g., rayon, cellulose acetate, cellulose nitrate, etc., and they deserve mention]
Several trade organizations serving producers and marketers of specific plastics are listed on a links page provided by the American Plastics Council.
Air emissions data for certain key criteria pollutants (ozone precursors) are available from the National Emission Trends (NET) database (1999), and hazardous air pollutant emissions data are available from the National Toxics Inventory (NTI) database (1996 is the most recent year for which final data are available). For SIC code 2821, Plastics materials and resins, the total emissions are:
The plastics sector contributes to greenhouse gas emissions from both fuel and non-fuel sources. Another document in this series, Greenhouse Gas Estimates for Selected Industry Sectors, provides estimates based on fuel consumption information from the Energy Information Administration (EIA) of the U. S. Department of Energy, and the the Inventory of U.S. Greenhouse Gas Emissions and Sinks, issued by the EPA. (The EIA document is sector-specific for energy intensive sectors, but does not provide emission data, while the EPA document provides emission data, but not explicitly on a sector-specific basis. See the estimates document for details of how the calculation was carried out). Based on those calculations, the plastics sector in 2000 was responsible for 68.1 teragrams (million metric tons, Tg) of carbon dioxide equivalent emissions from fuel consumption, and 9.9 Tg CO2 equivalent emissions (as nitrous oxide) from non-fuel sources (mostly for the production of adipic acid, a constituent of some forms of nylon), for a total of 78.0 Tg CO2 equivalent. In comparison, the chemical sector as a whole (including plastics) accounted for 531.1 Tg CO2 equivalent. Thus plastics is a sizeable contributor, but not the dominant contributor, to greenhouse gas emissions compared with the entire chemical sector.
A number of common monomers are known or suspect reproductive toxins or carcinogens. Examples include:
A special risk associated with products of the plastic sector is the leaching of plasticizers added to polymer formulations to improve material properties. An example is the concern over the leaching of the plasticizer DEHP from polyvinyl chloride used in medical devices. This was the subject of an FDA Safety Alert issued in 2002. Other phthalate plasticizers are found in a wide variety of consumer products, including children's toys, and food wrap. (Since phthalates are soluble in fat, PVC wrap used for meat and cheese is of particular concern.)
There are numerous finalized and proposed NESHAP rules that affect either processes or products of the plastics sector. They include:
Outside of general provisions in the Code of Federal Regulations, Title 40, Chapter 1, Subchapter N, Part 414 - Organic Chemicals, Plastics, and Synthetic Fibers, there do not appear to be Effluent Guidelines directed specifically toward plastics production. The guideline covered by Part 463 - Plastics Molding and Forming Point Source Category would apply more to the customers of the producers of resins than to the producers themselves.
An OECA Sector Notebook on Plastic Resin and Manmade Fiber is available at http://www.epa.gov/compliance/resources/publications/assistance/sectors/notebooks/resfibsn.pdf
Plastics industry economic data, provided by the American Plastics Council, is available at http://www.americanplasticscouncil.org/benefits/economic/economic.html