By W. L. Rathje

How long does it take for a newspaper to biodegrade in a landfill? What about plastic containers? Since the Garbage Project began digging landfills in 1987 and exhumed 40-year-old newspapers that were both intact and readable, not a week goes by without one or more local government, environmental group, company, teacher or student, or other interested individual asking the project's staff these kinds of questions. The reason for the questions, of course, is that quite a lot of people don't know the answer. And no wonder . . . .

There has been any number of media reports on the topic, and from my point of view they are usually contradictory, misleading, or downright wrong! Consider just one example, a "USA Snapshot" (the chart at the bottom left corner of USA Today's front page) on "Breaking down: How long it takes for some products to decompose," which appeared on November 13, 1989. The information given to readers: traffic ticket - 2-4 weeks; cotton rag - 1-5 months; aluminum can - 200-500 years; plastic six-pack ring - 450 years. The accompanying drawing showed a dozer rolling over such materials in what was clearly supposed to be a depiction of a landfill. The source of the information was Washington Citizens for Recycling.

How accurate is this information provided to educate the public? How many landfills did the Washington Citizens dig up to make these determinations? Who observed aluminum cans or plastic six-pack rings in landfills for a period of 200-500 years? I will venture to state that I don't believe the Washington Citizens conducted systematic digs and waste sorts at any landfills. Additionally, since aluminum cans and six-pack rings have only been manufactured for a few decades, I don't believe that anyone has observed those items or their disappearance during two or more centuries in landfills. In addition, the Garbage Project's digs of 18 "dry" landfills in Arizona, California, Florida, and elsewhere in North America have exhumed more than a few 20- or 30-year-old cotton rags and paper documents, including some traffic tickets.

I am extremely interested in decomposition issues because I was trained as an archaeologist. For more than 100 years, my colleagues have been methodically excavating and recording millions of buried discards from archaeological sites that are hundreds, even thousands, of years old. In fact, archaeologists are so interested in what happens to buried artifacts that they have a name for that particular area of study: Natural Formation Processes, or NFPs. When they begin a dig, excavators need to know whether they will unearth perishables that will require special equipment for continued preservation. And when they are interpreting the remains they have exhumed, archaeologists need to know whether or not finding wood or textiles means that none was buried or that if any were deposited, they would most likely have completely degraded or biodegraded. Altogether, the study of NFPs is a very important issue in archaeological research.

But no one interested in the breakdown of modern garbage seems to have queried my colleagues, who are specialists in long-term biodegradation. If they had, they probably would have been a little surprised and come to one important conclusion.

Surprises: How long do you think a buried ostrich plume would last? One remained preserved under the outer stone lid over Tutankhamen's sarcophagi in the Valley of the Kings in Egypt for more than 3,000 years. Of course, Egypt is very dry.

How long would intricately carved wooden objects last if they were covered by a very wet mudslide? Such objects were recovered by archaeologists at the site of Ozette in Washington state after almost 400 years of burial.

How long would a human body last in a marshland? Throughout Europe, some 20 "bog people" - several intact down to nose hairs and stomach contents - have been unearthed after 2,000 years of burial in one-time stagnant swamps.

Confusing? Yes. The result of "pyramid power" or some archaic magic? No.

For archaeologists, materials scientists, and microbiologists, one key decomposition concept is the distinction between "degradation" and "biodegradation." Degradation is the breakdown of materials from chemical interactions, such as metal that rusts when exposed to oxygen and plastic that becomes brittle with age and breaks into small pieces. Biodegradation is a breakdown of organic materials as a result of the action of microorganisms, such as food, leaves, or paper "rotting away."

For any kind of breakdown to occur, there must be a variety of prerequisites: time, aridity, fluid and its movement, presence of specific microorganisms, and so forth. The archaeologists' important conclusion: Each individual burial spot presents a different set of conditions and, thus, a different potential for both degradation and biodegradation. This is even true from day to day and load to load of refuse in the same landfill - clear versus rainy weather, different kinds and associations of food or paper or metal or plastic, stagnant versus moving fluids, and so on. That is the reason why there are no widely accepted rules of thumb for how long particular materials will take to decompose, because it all depends on the specifics of their burial context. In different contexts, the same carrot or piece of paper could last less than one year or more than 3,000.

There are some general guidelines archaeologists use to know what to expect to uncover when they begin digging.

First, contrary to a commonly held belief that fluid - and especially water - greatly speeds biodegradation, most archaeologists are elated to excavate a waterlogged site. In cases where perishable materials are thoroughly saturated with water and there are no significant currents - certain marshes, swamps, small lakes, fill behind retaining walls in harbors, and even outhouses - archaeologists have found papers, textiles, leather, and a variety of food intact after 100 to even 1,000 years of burial.

On the other hand, any archaeological site that goes through seasonal wet/dry cycles or that is submerged in moving water is not likely to produce many intact degradable or biodegradable remains. That is why the Garbage Project found clear evidence of significant biodegradation in the lowest lifts in New York City's unlined Fresh Kills Landfill, which began in 1948 on Staten Island in a swamp where tides wick water in and out of the bottom levels of refuse every day. This understanding of the role of moving fluids is behind the concept of bioreactor landfills, which are carefully designed to circulate leachate in an effort to facilitate biodegradation.

Knowing what kinds of garbage are likely to remain recognizable garbage is not just an arcane interest of archaeologists and landfill managers. Every discarder should know how much of what they throw out will likely be preserved for decades to come. Some people might feel that if paper items do indeed decompose in a very short time, why go to the trouble of recycling them? But wouldn't they feel differently if they knew that most paper doesn't decompose rapidly in standard landfills or that, even if it did biodegrade, microorganisms do not affect the lignin (the fiber element in paper) that comprises 40% or so of paper's volume?

At this point, I am sorry to report that public education about decomposition in landfills is way behind the times.

Last semester I gave a questionnaire to 63 students in an introductory class on natural science at the University of Arizona. Fully 30% of these college freshman believed that landfilled newspapers biodegrade in a matter of weeks. Another 57% responded that landfilled newspapers biodegrade within 10 years. OK, maybe 87% of the students are confusing newspapers buried in landfills with those they have seen decomposing as litter in the open.

But what about glass? Glass - vitrified sand of various forms - is an inorganic solid that is totally nonbiodegradable, and the only way it degrades is when it is broken up or ground into smaller and smaller pieces. Yet 24% of the UA freshman queried believed that glass biodegrades within 10 years of burial in a landfill.

Would the will to recycle increase if people knew more about what does and doesn't decompose rapidly in landfills?

Solid waste specialists - and archaeologists - have a lot of public educating and re-educating to do!

Contributing Editor W.L. Rathje is director of the Garbage Project.

MSW
MarchApril, 2001