Polystyrene foam, best known under the brand name Styrofoam, is a plastic with lots of uses. It insulates coolers and refrigerators. It cushions electronics for safe shipping. It holds drinks, yogurt and other tasty foods. It also makes a great snack for mealworms. And that could point to a new way to get rid of this long-lived plastic.
This and other types of plastic currently present big problems. They take up lots of space in landfills. And some types of plastic, including polystyrene, can resist breakdown for a long, long time, notes Wei-Min Wu. He’s an environmental engineer at Stanford University in California.
Polystyrene is a polymer. It is made of a long chain of repeating groups of atoms. The chemical structure of those units makes it very stable and long lasting. “People thought this compound could take a hundred years to be broken down,” Wu says. The food that polystyrene protects, in contrast, can decompose in as little as a month.
However, a new study finds, hungry young insects can speed the plastic’s breakdown. Feed polystyrene foam to common mealworms, and in just one day their gut bacteria can break down almost half of the foam they ate.
Wu led the team doing this research along with environmental engineer Jun Yang at Beihang University in Beijing, China. They published their new findings in Environmental Science & Technology on September 21.
Mealworms are the immature, or larval, form of Tenebrio molitor beetles. For one month, the researchers fed only polystyrene foam products to a test group of these yellow, wormlike larvae.
The mealworms that ate plastic were generally every bit as healthy as the controls — those eating normal food. Chemical tests showed that the plastic-eaters used the polystyrene as they would any food — for energy to fuel their life activities. After 16 days, about half of the carbon from the polystyrene came out of the mealworms as waste. Most of the rest was converted to carbon dioxide. Carbon dioxide is a byproduct of respiration by species that breathe oxygen. Respiration uses the oxygen to break down chemical compounds for energy.
Additional work showed that gut bacteria in the mealworms performed much of the plastic’s breakdown. But just taking the bacteria out of the mealworms won’t solve society’s growing problem of plastic wastes. Those bacteria will break down polystyrene when they’re outside of a larva's gut. However, says Wu, “the rate is much slower than inside the mealworm’s body.” After two months, those bacteria broke down 7 percent of the compound. Inside the bugs, about half of the chemical broke down in just one day.
“This appears to be very good research,” says Susan Selke. She’s a chemical and packaging engineer at Michigan State University in East Lansing. She warns, though, that the discovery isn’t a cure-all for polystyrene wastes.
It is important to know that mealworms can break down this otherwise long-lived plastic. “But that doesn’t mean that if you throw your polystyrene cup away improperly that it’s going to be degraded,” she says. When it ends up in a landfill, that cup will stick around for a very long time.
And this research isn’t a reason to rush out and release mealworms or bacteria near landfills, she warns. “There could be all sorts of potential consequences [unwanted changes] to the environment.” Moreover, she notes, the cost of buying up a truckload of the bugs to treat those wastes could be quite high.
Wu agrees that it’s best to view the new research as a first step. For now, the researchers know what the mealworms can do. The next step will be figuring out which enzymes from their gut bacteria trigger the breakdown of the plastic chemical. Only later on might engineers apply that knowledge to actually treat some plastic wastes.
Meanwhile, all consumers need to do their part in helping to reduce the amount of plastic that ends up in the trash. “Plastic contamination is a real problem,” Wu says. “We need to enforce recycling and separation of plastics from the trash.” Both can limit how much plastic ends up in the environment while researchers seek out better ways to eliminate that trash.
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atom The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and neutrally charged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.
bacterium (plural bacteria) A single-celled organism. These dwell nearly everywhere on Earth, from the bottom of the sea to inside animals.
carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.
carbon dioxide A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter (including fossil fuels like oil or gas) is burned. Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food. The abbreviation for carbon dioxide is CO2.
chemical A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
chemical engineer A researcher who uses chemistry to solve problems related to the production of food, fuel, medicines and many other products.
compound (often used as a synonym for chemical) A compound is a substance formed from two or more chemical elements united in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
control A part of an experiment where there is no change from normal conditions. The control is essential to scientific experiments. It shows that any new effect is likely due only to the part of the test that a researcher has altered. For example, if scientists were testing different types of fertilizer in a garden, they would want one section of it to remain unfertilized, as the control. Its area would show how plants in this garden grow under normal conditions. And that give scientists something against which they can compare their experimental data.
degrade (in chemistry) To break down a compound into smaller components.
engineer A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.
environment The sum of all of the things that exist around some organism or process and the conditions they create for that organism or process. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature, humidity and placement of components in some electronics system or product.
environmental engineer A person who uses science to study and improve the natural environment.
enzymes Molecules made by living things to speed up chemical reactions.
gut Colloquial term for an organism’s stomach and/or intestines. It is where food is broken down and absorbed for use by the rest of the body.
landfill A site where trash is dumped and then covered with dirt to reduce smells. If they are not lined with impermeable materials, rains washing through these waste sites can leach out toxic materials and carry them downstream or into groundwater. Because trash in these facilities is covered by dirt, the wastes do not get ready access to sunlight and microbes to aid in their breakdown. As a result, even newspaper sent to landfill may resist breakdown for many decades.
larva (plural: larvae) An immature life stage of an insect, which often has a distinctly different form as an adult. (Sometimes used to describe such a stage in the development of fish, frogs and other animals.)
mealworm A wormlike larval form of darkling beetles. These insects are found throughout the world. The ever-hungry wormlike stage of this insect helps break down — decompose, or recycle — nutrients back into an ecosystem. These larvae also are commonly used as a food for pets and some lab animals, including chickens and fish.
plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.
polymer Substance whose molecules are made of long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example).
polystyrene A plastic made from chemicals that have been refined (produced from) crude oil and/or natural gas. Polystyrene is one of the most widely used plastics, and an ingredient used to make a widely used white, rigid foam (often sold under the name Styrofoam).
recycle To find new uses for something — or parts of something — that might otherwise by discarded, or treated as waste.
respiration The process by which organisms produce energy from sugars, usually by taking in oxygen and releasing carbon dioxide.
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Original Journal Source: Yu Yang et al. Biodegradation and mineralization of polystyrene by plastic-eating mealworms. Part 1. Chemical and physical characterization and isotopic tests. Environmental Science & Technology. Published online, September 21, 2015. doi: 10.1021/acs.est. 5b02661.
Original Journal Source: Yu Yang et al. Biodegradation and mineralization of polystyrene by plastic-eating mealworms: Part 2. Role of gut microorganisms. Environmental Science & Technology. Published online, September 21, 2015. doi: 10.1021/acs.est.5b02663.