A cup made from PLA, plastic made from cornstarch.
Image: Bec, courtesy Flickr
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The Best Science Writing Online 2012
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Dear EarthTalk: What are the environmental pros and cons of corn-based plastic as an alternative to conventional petroleum-based plastic?
-- Laura McInnes, Glasgow, Scotland
Polylactic acid (PLA), a plastic substitute made from fermented plant starch (usually corn) is quickly becoming a popular alternative to traditional petroleum-based plastics. As more and more countries and states follow the lead of China, Ireland, South Africa, Uganda and San Francisco in banning plastic grocery bags responsible for so much so-called “white pollution” around the world, PLA is poised to play a big role as a viable, biodegradable replacement.
Proponents also tout the use of PLA—which is technically “carbon neutral” in that it comes from renewable, carbon-absorbing plants—as yet another way to reduce our emissions of greenhouse gases in a quickly warming world. PLA also will not emit toxic fumes when incinerated.
But critics say that PLA is far from a panacea for dealing with the world’s plastic waste problem. For one, although it does biodegrade, it does so very slowly. According to Elizabeth Royte, writing in Smithsonian, PLA may well break down into its constituent parts (carbon dioxide and water) within three months in a “controlled composting environment,” that is, an industrial composting facility heated to 140 degrees Fahrenheit and fed a steady diet of digestive microbes. But it will take far longer in a compost bin or in a landfill packed so tightly that no light and little oxygen are available to assist in the process. Indeed, analysts estimate that a PLA bottle could take anywhere from 100 to 1,000 years to decompose in a landfill.
Another issue with PLA is that, because it is of different origin than regular plastic, it must be kept separate when recycled, lest it contaminate the recycling stream. Being plant-based, PLA needs to head to a composing facility, not a recycling facility, per se, when it has out served its usefulness. And that points to another problem: There are presently only 113 industrial-grade composting facilities across the U.S.
Another downside of PLA is that it is typically made from genetically modified corn, at least in the U.S. The largest producer of PLA in the world is NatureWorks, a subsidiary of Cargill, which is the world’s largest provider of genetically modified corn seed. With increasing demand for corn to make ethanol fuel let alone PLA, it’s no wonder that Cargill and others have been tampering with genes to produce higher yields. But the future costs to the environment and human health of genetic modification are still largely unknown and could be very high.
While PLA has promise as an alternative to conventional plastic once the means of disposal are worked out, grocery shoppers could do well to by simply switch to reusable containers, from cloth bags, baskets and backpacks for grocery shopping (most chains now sell canvas bags for less than a dollar apiece) to safe, reusable (non-plastic) bottles for beverages. As for other types of PLA items—such as those plastic “clamshells” that hold cut fruit (and there is a whole host of industrial and medical products now made from PLA)—there is no reason to pass them by. But until the kinks are worked out on the disposal and reprocessing end, PLA may not be much better than the plain old plastic it’s designed to make obsolete.
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11 Comments
Add CommentPLA is touted as carbon neutral? Has anyone done an assessment of the energy inputs required to grow and harvest the corn and then convert it to PLA and compared them with those for producing conventional plastic? Since the carbon in a conventional plastic isn't released unless it is burned the energy inputs in manufacture are what determine the carbon footprint, not where the carbon in the plastic came from. From this standpoint I strongly suspect PLA products actually score worse than traditional plastics in terms of atmospheric carbon release.
Reply | Report Abuse | Link to thisThis is a remarkable effort to reduce CO2 by changing mind set from normal plastic to bio-degrable plastic consumption.I thing if you burn, it is produce less pollution than normal plastic burning. Most important is that if society is not able to handle the plastic, than nature will take care of without any harmful effect . Whereas in normal plastic if not collected, left for natural degradation it may take 500years in somekind of plastic. Till than plasic location site can not produce anything. most of the drainage system clogged in INDIA and many other nation. Many animals (COWS) eat up this plastic & died by clogging of their instentine.
Reply | Report Abuse | Link to thisrcdohare25@yahoo.co.in
Although its usefulness is still questioned, I think we can all agree that this is a first step towards a greener earth. There may be more questionable inventions or ideas, but the important thing is that we as a society are actually more and more concerned about our environment.
Reply | Report Abuse | Link to thisPlease keep in mind that genetically modified crops have a known upside in addition to "unknown future costs." These crops are measurably increasing yields while reducing the demand for fertilizer, pesticides, and water. And while gene splicing is a new technique we have been modifying wild plants to make crops for thousands of years.
Reply | Report Abuse | Link to thisAll the best,
Paul
I think you're right. It's important to focus on the benefits and try to support new, environment-friendly ideas. Every idea needs to be supported, because if it's not good in itself, it might be a predecessor to a better one.
Reply | Report Abuse | Link to thisI'm not at all thrilled about PLA. Plastics are just as carbon neutral -- that whole
Reply | Report Abuse | Link to thisMy comment got chopped...
Reply | Report Abuse | Link to thisI'm not at all thrilled about PLA. Plastics are just as carbon neutral -- that whole not degrading in landfills thing. It's got the same carbon effect as leaving the petroleum underground. And PLA requires a TON of energy in fertilizer, transport and processing putting its production closer (tho i don't have numbers) to the impact of plastic.
Furthermore, while PLA can't be recycled, plastic can. A compostable plastic would be wonderful. But you just try composting PLA container in your compost -- it doesn't break down and (like the article said) proper infrastructure does not yet exist.
So, how about we just stick with conventional plastic when plastic is necessary? We can use more fiber based materials where appropriate and reuse more.
But PLA, it's green washing to me. Just because it comes from a plant doesn't mean it's natural or better for the environment.
One big issue with plastic is that it finds its way into the marine environment. It may be that PLA products degrade faster than petroleum products in the oceans. This alone would be worth the effort of conversion, as petroleum plastics are not broken down in the ocean and are causing a large impact to marine life when ingested. Since we are at the top of the sea-food food chain, we will ultimately be ingesting these chemicals.
Reply | Report Abuse | Link to thisThere are a lot of problems with PLA - If we made all of the plastic disposable items used in the world every year, it would take one hundred million tons of corn to make it. That would lead to mass starvation in the third world, as that represents at least 10% of the world's grain supply. Also, in landfills, PLA exudes methane when it decomposes-and methane is a potent greenhouse gas. It also takes a huge amount of diesel to grow, fertilize, ship, and process this corn. As a practical matter, it is also not recyclable. The alternative? Oxo-biodegradable plastics. See http://biogreenproducts.biz for full information. -Tim Dunn
Reply | Report Abuse | Link to thisWe are all responsible to openess to a future that embraces many solutions; landfill managment to tap into the vast energy resource now dormant, PLA has identified a need for biopolymers in a world where recycling is less than 5% of total plastic processed. The huge balance of plastic waste is a source of energy, recycled efficiently waste plastic is a source of carbon saving in new products. The ability to make existing polymers biodegradeable is also a new technology that taps into the solution offered by the PLA technology but without affecting the water, land, fertilizer, etc. intensity needed to support a farmed base raw material source.
Reply | Report Abuse | Link to thisThis argument is settled quite quickly by referring to an article published in August, 2000 in Scientific American Magazine. in it, two American Scientists from two separate Universities, published their findings on this subject.
Reply | Report Abuse | Link to thisIt clearly states that although the main goal of PLA was to reduce our dependance on Petroleum Products by replacing conventional plastics with the PLA Corn Based alternative, it does just the opposite. PLA actually uses more Petroleum Energy than regular Plastics. So right off the start it has failed it's main purpose. Add to this the fact that Corn uses more Nitrogen than any other food and this runs off, down to the rivers and eventually the oceans, thereby creating Dead Zones devoid of Oxygen in which no life can survive. We now have a 10,000 square mile Dead Zone just off the Mississippi Delta which continually grows due to excess Nitrogen and other chemicals, pesticides, etc.
Gasoline takes 1 gallon of water to drive a car 1 mile.
Ethanol takes 90 gallons of water to drive a car 1 mile.
45% of US Corn production goes to making Ethanol and PLA.
Corn prices are rocketing up and so are the death rates of 3rd world children who cannot afford Cornmeal anymore.