Monday, October 12, 2009

The Curse of the Mummy's Tomb: Landfill and Biodegradation

Archeology and paleontology are not always glamorous jobs. There’s very little Indiana Jones, for instance, to excavating middens – ancient heaps of trash left behind by ancient peoples in ancient holes (or by ancient animals, such as packrats, in ancient holes.) Yet, despite the fact that it’s basically time-lapse dumpster-diving, you can find a lot of neat stuff in middens. Stone tools, metal artifacts, and shards of pottery. Oyster shells and the preserved bones of, say, a Great Auk. And bits of plants.

Bits of plants? Yes. Because one of the many interesting facts that middens demonstrate is that biodegradation, although it seems like a powerful and immutable law of nature, is surprisingly easy to thwart. Lack of oxygen and sunlight, the wrong temperature, or the absence of suitable microbes can slow it to a crawl. Thus prehistoric packrats, who had never even heard of a time capsule or a paleontologist and probably wouldn’t care if you told them, were able to preserve grains of pollen, leaves and stems in such conditions that they eventually fossilized rather than breaking down into the soil and can be identified to the species level today.

Modern landfills have come a long way from the old principle of digging a hole and tipping the waste in. For perfectly good reasons like keeping toxic sludge out of the surrounding air, water, and soil, today’s landfills are sealed up far tighter than any packrat could ever dream of. In addition, they are compacted using heavy machinery, which results in still darker, drier, more anaerobic conditions on the inside.

The results are startling: University of Arizona researchers excavated landfills in three states, and discovered well-preserved 25-year-old hot dogs, half-eaten steaks and even grapes as well as 40-year-old newspapers that could still be read; they estimated that food refuse in the landfills they excavated decomposed by only about 50% every twenty years. Meanwhile, that fifty percent that does decompose doesn’t just disappear innocuously; it produces quantities of methane, which has been implicated in global warming, and liquids appetizingly known as leachate. Leachate can be contaminated with almost anything that the indiscriminant mingling of decades of household wastes might bring to the party – heavy metals, PCBs, dioxins and more.

Read the rest of this article on page 14 of the April 23, 2009 Linewaiter's Gazette.

Photo courtesy of D'Arcy Norman.

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