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A regulatory tangle.

A Regulatory Tangle

Degradable plastics are an ironic about-face for the plastics industry. For years, polymer chemists have worked to make plastics stronger, more inert, resistant to chemical and microbial attack, and more durable. However, the very success of plastics has created problems.

Because of their strength and durability, there is a growing concern that plastic wastes will accumulate in the environment, leading to long-term environmental and waste management problems. It is estimated that 1 million tons of plastics are dumped in the ocean annually. Up to 69 percent of all beach and harbor litter is made up of plastics. The Congressional Office of Technology Assessment (OTA) reports that tens of thousands of sea birds and an estimated 100,000 marine mammals die each year by ingesting or becoming entangled in plastics debris.

The concern about plastics coincides with a steep decline in the number of landfill sites where the wastes may be deposited, as well as a growing opposition to these sites. In 1986, plastics accounted for an estimated 10 million tons, or about 7 percent by weight, of the 158 million tons of municipal solid waste (MSW) generated. Present estimates of volume contributed by plastics vary from 14 to 21 percent. By the year 2000, it is estimated that about 9 percent of MSW or 16 million tons will be contributed by plastics.

Renewed Interest

Popular concern has influenced legislation. Several hundred solid waste bills involving plastics are being debated in state, local, and municipal legislatures. Some bills threaten to ban the use of nondegradable products, like packaging, entirely. Others call for mandatory recycling or degradability. Some states have enacted relatively simple legislation without delving into the more technical aspects of plastics degradability. Other states have tried to define degradability more exactly or have addressed the issue of plastic six-pack connecting rings. At least one-third of the states currently require six-pack rings to be degradable.

Developing Regulations

Before the application of degradable plastics technologies can be promoted, the uncertainties surrounding them must be addressed. Currently, the effect of different environmental settings on their performance is not understood. Issues relating to performance include the possibility that degradation may occur before the product has served its useful purpose, or occur too slowly to provide an effective solution to environmental problems. In addition, the products or residues of degradable plastics and the environmental impacts of these residues have not been fully identified or evaluated. Safety issues include the potential toxicity of chemicals leaching from degradable plastics and the size of the plastic fragments resulting from degradation, which may pose a threat to wildlife. And the impact of degradable plastics on recycling is unclear.

Perhaps most important, the precise meaning of degradability needs to be determined. Definitions of such basic terms as photodegradable and biodegradable have not yet been developed. Such definitions are an ideal starting point for developing standards and regulations.

Various officials in the federal and private sectors are concerned that the current lack of standards may lead to unenforceable and confusing laws. As is often the case in environmental regulations, the laws drive the research, and it can be disastrous if the regulations aren't correct. Laws in nine states provide no definition of degradable plastics, 10 states specify no time frame for degradability, and 11 states provide no requirement regarding the safety of the end products.

At Senate hearings last year, Joan Harn, an OTA analyst who worked on degradable plastics as part of a MSW study, noted, "At this time we have insufficient knowledge of the mechanisms of plastics degradation and the possible effects of the degradation products on the environment to be able to write effective standards. More research will be needed to determine the kinds of test procedures required." It typically takes three to five years for standards to be developed through organizations such as ASTM, even with technologies more mature than this one. However, ASTM is accelerating the process and may have consensus standards within a year.

The U.S. Environmental Protection Agency (EPA), U.S. Food and Drug Administration (FDA), and National Institute of Standards and Technology (NIST) would be the appropriate agencies for such an activity because of their experience in testing for environmental effects and product performance. Officials recognize the need for degradable plastics standards, but relatively little effort is currently under way.

Just defining test methods and standards for biodegradability is a difficult task. Conditions vary in different states and in different environments within each state. The conditions found in a municipal landfill differ from those found in water. The variety of conditions encompass very different temperatures, access to sunlight, microorganisms, and sources of nutrients for the microorganisms.

"You can't come up with a test method that will measure the biodegradability of a material in all those environments simultaneously," said Leslie Smith, chief of NIST's Polymers Division. "You need different test methods for different environments and you have to come up with some kind of agreement as to what those are."

Uncertain Performance

At first glance the benefits of biodegradable plastics seem obvious: put the plastics in a landfill and let the action of microorganisms reduce them to something innocuous, in much the same way that composted grass clippings go away. However, there is now evidence that degradation rates in landfills are very slow for all materials.

According to Jack Pincus, vice president for economic development of the Michigan Biotechnology Institute (East Lansing, Mich.), "Landfills are not optimum environments for biodegradation. They are devoid of moisture and oxygen and limited in microorganisms that can biodegrade certain materials. This problem transcends biodegradable plastics and concerns all organic materials disposed of in landfills. Therefore, the issue is not the implication of landfill conditions for biodegradable plastics, but how conditions in landfills can be changed to increase degradation."

Currently, 50 percent of MSW is degradable material. But because landfills lack oxygen or water, they would have to be wet and stirred like compost, to create an environment in which the biodegradable material could degrade. Otherwise, as Smith pointed out, "There will be quite an expense in developing and marketing materials that will have little effect."

According to a 1990 EPA report on methods to manage and control plastic wastes, those wastes affect landfill capacity because of the growing amount of wastes produced, not because they are not degradable.

Although much of the interest in degradable plastics has been stimulated by concern about marine litter, few tests have been conducted on the degradability of existing plastic products in seawater. Limited seawater testing on materials now used on six-pack rings, as well as polyethylene and polystyrene products commonly found in marine debris, has been completed by the Research Triangle Institute (Research Triangle Park, N.C.) for the Northwest and Alaska Fisheries Centers. The limited data available suggest that photodegradation rates are somewhat reduced in marine environments, making plastics a more persistent problem in water than on land.

How degradable plastics will behave in food applications is also uncertain. According to Lloyd Robert Lake, director of the FDA's Office of Compliance, "There is currently a lack of very basic information underlying this technology which is critical to a safety review. It is essential to know the identities of the substances which may be added to plastics in order to make them degradable, their toxicological significance to humans, and how these substances affect polymers in order to impart degradability."

The FDA's assessment of food safety includes concerns about the shelf-life of degradable packaging and potential food contamination. The agency places the burden of proof for the safety of a new product, as well as its environmental impact, on the manufacturer. Although the FDA has yet to be presented with a degradable plastic to review for food applications, its Canadian counterpart, the Agency of Health Protection of the Department of National Health and Welfare, has already approved using degradable cups in place of nondegradable plastic ones.

One of the most difficult issues in degradable plastics is their potential burden on the environment. "No one has a problem with small amounts of degradable plastics," said Smith, "but if one really got serious about it to the extent that it would affect the volume of municipal solid waste, then, in effect, you're taking plastics that are inert and cause no significant environmental hazard and instead creating plastics that have effects on the water and air. That's not an easy trade-off."

Though photodegradation doesn't produce organic compounds that are generally considered toxic in large amounts or concentrations some products--solvents like acetone and methyl ethyl ketone (MEK)--are not benign.

"From another standpoint, we spend a lot of time and money taking chemicals and hazardous materials and trying to make them inert, so that we can put them in landfills," said Smith. "Here, we're taking inert materials, because we don't want to deal with the issues of disposal and recycling, making them break down, and perhaps causing more environmental damage. So it's a double-edged sword in that potential environmental consequences have to be faced in any discussion of degradable plastics."

To date, very little data are available on degradation byproducts and their effect on the environment. It is possible that nondegradable plastic products may actually pose fewer environmental risks in landfills today than degradable plastics. According to the EPA, plastic polymers don't represent a hazard of toxic leachate formation when disposed in landfills. In addition, current data are too limited to deermine whether additives in plastics contribute appreciably to the toxicity of MSW landfill leachate.

Another major concern is the size of the initial fragments that result from degradation. Scientists are concerned that degradable plastics may serve only to substitute one hazard for another--increased ingestion for less entanglement. The ingested fragments fool wildlife into feeling as if they had eaten, and they subsequently starve and die.

A further complication is that when plastics degrade, regardless of the mechanism, they give off gases such as carbon dioxide, which contributes to the greenhouse effect. And under anaerobic conditions, microorganisms can produce methane, which contributes to the formation of smog.

Recycling Efforts

The plastics industry contends that degradable plastics might threaten the physical integrity of recycled products, reverse increases in recycling, and cause complicated liability problems. Technical experts working with degradable plastics disagree and believe that countermeausres can be taken. They contend that poential adverse effects will vary depending on the particular degradable plastic and that the problems will be minimized by diluting the material and adding appropriate steps to the recycling process (such as separation of degradables, chemical treatment, and the use of additives) to negate any effects of degradable materials.

"There are many possible ways to mitigate the effects of degradable plastics on recycling efforts, but we are not aware of any which could be widely applied at low cost," said Bruce Weddle, acting director of the EPA's Municipal Solid Waste Program. "The expanded use of degradable plastics and promotion of recycling may demand compromises. Large amounts of degradable plastics in the waste stream will add to separation and processing costs and may limit the market value of the recycled products. From the standpoint of the science and technology aspects of the material properties and processes associated with recycling, the presence of degradable plastics in the waste stream definitely complicates recycling."

The greatest objection, however, focuses on recycling degradable plastics containing starch. Moisture absorption is a problem in manufacturing bags, so the starch is treated to make it water resistant. But moisture is needed when trying to recycle the bags. As a result, widespread use of plastics that incorporate starch could be a tremendous blow to industrial sector recycling. (Currently, virtually all polyethylene-film industrial scrap is recycled in-house by the companies that use it.) One Canadian company claims to have a waterfree process that it uses to successfully recycle starch-filled plastic scrap from manufacturers of diapers and garbage bags.

At this stage of development and application, the issue of degradable plastics negatively affecting recycling may not be a real one, because significant numbers of plastic bags are not recycled now and they are pretty low in the hierarchy of what will be recycled in the future. According to Anthony Andrady, a researcher at the Research Triangle Institute, "Politically, it is appealing to collect and recycle all plastics; but economically, it is not cost effective in the case of some types of plastic products." Nonetheless, environmental groups fear that the perception that plastics degrade will lower the public's interest in recycling programs.

Beyond a few niches, there may be no significant market for degradable plastics unless it is legislatively mandated, since all degradable plastic materials are more expensive than nondegradable materials. "Unfortunately, degradable plastics were oversold in the past and the public was led to believe it's a magic answer to most of the solid waste problem," said Andrady. "With more information becoming available, people are beginning to appreciate its capabilities and recognize its limitations." Degradable plastics may play a role in moderating some of our waste problems as part of a more comprehensive approach, but care must be taken to consider and avoid new problems in implementing the technology.

Though many questions about the technology of biodegradable plastics have been raised, little effort in answering these questions is under way. Most of the $2 million in annual U.S. federal funding for degradable plastics emphasizes the development of new materials rather than sandards. to make greater use of degradable plastics, much more research remains to be done on their properties, the degradation mechanism, and the degradation products. There is still a great deal to learn about the potential uses and misuses of these materials.

According to Hanik, "The plastics industry is a highly technologically capable and creative one and it may be that any and all of the various degradation technologies could, with significant additional research, be developed to work effectively in different environments. But that answer is down the road and the presumption that it will occur should not be made at this time."
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Title Annotation:Degradable Plastics
Author:Rosen, Jerome
Publication:Mechanical Engineering-CIME
Date:Jul 1, 1990
Previous Article:Designed to break down.
Next Article:Process control takes command.

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