The Right Chemistry: ‘Biobased’ or ‘biodegradable’ sometimes is biobunk

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Consumers are increasingly conscious of environmental issues, but goods’ environmental impacts may not always be what they seem.

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When it comes to marketing, the prefix “bio” boosts sales. Consumers, increasingly conscious of environmental issues, are attracted by terms like “biodegradable” and “biobased” on product labels. Certainly, the prospect of a conventional plastic bag or discarded water bottle being around for 500 years is not appealing. More comforting is the thought of a biodegradable plastic that decomposes through the action of bacteria or fungi into components that have no adverse impact on the environment. While there are ways to produce biodegradable plastics, the problem is that they decompose only under ideal conditions and in an unpredictable time frame. Experiments have shown that a supposedly biodegradable bag buried in soil or cast into the ocean undergoes almost no change in three years. “Compostable” plastics are more environmentally friendly, but only as long as they end up in an industrial composting facility.

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These days the term “biobased” is appearing on labels with increasing frequency. “Bio” comes from the Greek for “life,” so that a “biobased” product suggests the material from which it is made originates from a renewable living source rather than from non-renewable petroleum. The assumption is that biobased substances have a lower environmental impact in terms of greenhouse gas emissions, and have more sustainable supply chains. However, a closer examination suggests that these benefits are quite nuanced.

“Surfactants” are molecules that have a “hydrophilic head” that is attracted to water and a “hydrophobic tail” that favours oily substances. This structure makes them ideal for removing greasy stains from surfaces and accounts for their use in laundry products. Surfactants also find widespread application in cosmetics where they allow oily and aqueous phases to blend together smoothly. Most surfactants are produced synthetically and source at least some of their components from petroleum. For example, sodium lauryl ether sulphate (SLES), one of the most widely used surfactants, is made from lauryl alcohol and ethylene oxide. The lauryl alcohol is produced from palm kernel oil or coconut oil, while the ethylene oxide is made from ethylene derived from non-renewable petroleum or natural gas.

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Were the ethylene to be produced from plants, then the SLES could be described as “100 per cent biobased.” Great for marketing! Indeed some manufacturers of biobased SLES aim to attract their customers, the major detergent and personal care product companies, by offering proof that no petroleum derivatives have been used in their synthesis. That proof lies in the demonstrated absence of any carbon-14 isotope.

When cosmic rays, high energy particles that originate in outer space, bombard the Earth’s atmosphere, they produce neutrons that can knock a proton out of the nucleus of a nitrogen atom and convert it into the C-14 isotope. The result is that about one in every trillion carbon dioxide molecules in air has a C-14 atom instead of C-12. Since carbon dioxide from the air is the source of all carbon atoms in plants via photosynthesis, living plants will contain some C-14. But carbon-14 is radioactive and has a half-life of about 5,700 years, which means that petroleum formed from living matter at least 65 million years ago, no longer contains any C-14. A consequence is that compounds derived from petroleum will not contain any of this isotope, while those originating in living matter will have some.

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But “100 per cent biobased” SLES does not necessarily make it more “green.” First, although the lauryl alcohol does come from a plant source, there is quite a bit of processing involved. Fats have to be broken down to yield lauric acid, which is then converted to lauryl alcohol by reaction with hydrogen. Both these processes require the use of fossil fuels. That holds true whether the SLES is synthetic or biobased. The other key component, the ethylene needed to make ethylene oxide, instead of petroleum, can be made from ethanol, that in turn is produced by fermenting corn or sugarcane. With both lauryl alcohol and ethylene oxide then being derived from plant sources, the “100 per cent biobased” claim can be sort of justified.

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Corn and sugar cane are renewable resources, and petroleum of course is not. However, that does not necessarily mean that biobased ethylene oxide has a smaller environmental footprint. There are significant greenhouse gas emissions associated with growing corn or sugar cane. These crops require pesticides and fertilizer, the production of which relies on fossil fuels, and then there is the fuel needed for the trucks and farming equipment required. Overall, biobased SLES may be associated with somewhat less greenhouse emission, but the overall impact is not likely to be highly significant unless the ethanol is fermented from waste straw and the CO2 produced by fermentation is captured.

Instead of a biobased surfactant, how about a “biosurfactant?” Some microbes produce glycolipids, natural molecules that have hydrophilic and hydrophobic parts and can act as surfactants. They can be produced by a specific strain of yeast isolated from honey. While no chemical synthesis is involved, the problem is that the yeast has to be fed raw materials in the form of sugar or sunflower oil. These require the use of agricultural chemicals that have a significant carbon footprint.

What’s the bottom line here? That determining the environmental impact of consumer items is complicated and the prefix “bio” does not necessarily mean better. Careful analysis is needed to distinguish between “biobased” and “biobunk.”

[email protected]

Joe Schwarcz is director of McGill University’s Office for Science & Society (mcgill.ca/oss). He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 to 4 p.m.

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