Using bugs to build better bags and bottles
One Saturday morning recently, a bunch of us spent part of a community cleanup day picking up trash along the roadsides. It was a day of good news and bad news. The good news is that Maine's bottle law is clearly working. Those who remembered a similar cleanup before the 1978 bill went into effect were impressed at how few soft-drink and beer bottles they found this time.
The bad news is that the bottles are being replaced by things that may be even worse: polystyrene cups, polyethylene six-pack yokes, and fast-food containers. Biodegradable? Not in my lifetime.
If our grandchildren turn out for cleanups 30 years from now, they may well find the cup someone tossed out yesterday.
So I'm encouraged by a couple of items that crossed my desk recently. One was small, local, and immediate: Maine's two largest supermarket chains, Shaw's and Shop 'n Save, have replaced their standard plastic carry-out bags with ``bio bags'' that decompose more quickly in landfills. The new Canadian-made bags contain particles of cornstarch that bacteria feed on when the bag is discarded.
That's good. But it's not the ultimate solution. The bag, which is still largely made of plastic, does indeed decompose. But the tiny particles of plastic remain. That's the nature of a petroleum-based plastic: ``Every ounce, once it's produced, is there forever - unless it's incinerated,'' says Prof. R. Clinton Fuller, a biochemist at the University of Massachusetts, Amherst.
Dr. Fuller, no stranger to plastics, is largely responsible for the second encouraging item. With his colleague Robert W. Lenz, a professor of polymer science and engineering, he's busy solving the roadside problem at its roots.
The secret, he says, lies in the fact that certain bacteria, when subjected to abnormal stress, produce polyesters. That's right, polyesters: the stuff of inexpensive cloth, disposable diapers, industrial containers, and a 1,001 other uses. The bacteria does it, says Fuller, for much the same reason that a bear going into hibernation puts on fat - to store up a potential energy supply. Give a bacterium like Rhodospirillum rubrum sunlight, garbage, and stress, and it cranks out granules of polyhydroxyalkanoates - a family of polyesters known in the trade as PHAs - in large quantities.
In itself, that's nothing new. Bacteriologists have known about PHAs since 1925. But three things suddenly make it relevant:
PHAs are thoroughly biodegradable - obviously, since the bugs made them in order to eat them later. Throw PHAs into sewers, landfills, or wherever R. rubrum and a variety of other bacteria live, and in a few months they're nothing but soda water - carbon dioxide and H2O, two of the commonest constituents of the biosphere.
Bacteria can make entirely new classes of plastic - mixed polymers, or copolymers, that have intriguing properties related to their stiffness, melting point, breakage, and resistance to organic solvents. Fishing nets, insulation, windshields - the possibilities are myriad.
These polymers, unlike many petroleum-based plastics, are slightly heavier than water - which helps explain why Fuller and Dr. Lenz are being supported by grants from the Office of Naval Research.
A report cited in a recent issue of Smithsonian Magazine estimated that merchant ships dump 450,000 plastic containers each day into international waters. If they all sank - and then degraded - the seas would be far cleaner.
Fuller sees potential commercial applications coming within a few decades. The technology, he says, is not complicated - about like brewing beer. So far, however, costs are steep: A small British firm, Marlborough Biopolymers Ltd. (a subsidiary of Imperial Chemical Industries), is now producing for about $5 a pound what makers of petroleum-based plastic sell for 50 cents a pound.
Why, then, is bacterial plastic the wave of the future? Because, in a rare reversal, need is driving technology: Society, rather than responding to inventions, is demanding them. Landfills across America are fast filling up. Yet humanity is not about to give up plastic.
Nor, if Fuller and Lenz are right, will we have to. Exit the manufacturing process that began with nonrenewable crude oil, passed through smelly refineries, and ended with an environmental hazard. Enter the process that begins with garbage, passes through a vat, and ends with soda water. A Monday column