Materials News
Can plastics co-exist with nature? Plastics and nature are like oil and water: they do not seem to mix. However, a number of discoveries have shown that the two actually share a recipe to co-exist, says Angelica Buan in this report.
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aste plastics, the result of increasing urbanisation and industrialisation, are posing health hazards to the environment, human and animal lives. For the hundredth time, plastics have been cited as a felon in climate change, marine litter, flooding, and other hosts of environmental malaise. As well, the toxicity and leaching of plastics have led to recalls of products packaged with plastics. But believe it or not, plastics and nature can co-exist in a way that is mutually beneficial and nutritious, too. The complementary role of plastics and nature is highlighted in some recent and previous discoveries and developments showing plastics can serve as nourishment for some organisms to perpetuate their life cycle. On the other hand, nature can play a role in producing plastics, as well as aiding plastics to become environmentally friendly. Meanwhile, our search for “green” packaging material has carved out gastronomic developments in packaging, which is hoped to help create a zero-waste society in the near future. Your trash, their food Take-out meals in Styrofoam packaging spell convenience but undoubtedly contribute significantly to the growing heap of this material in landfills. It is also generally not accepted in recycling centres in many countries and, citing a finding from the CleanWater Action study, is said to be “not clean enough to be recycled”. Thus, it has a low recycling rate, and, like other plastic types, photodegrades, which experts believe only breaks it down into tiny pieces but not disappear completely from the environment. The mountains of Styrofoam waste may not be appealing to environmentalists, but it is for mealworms, which is the larvae form of the darkling beetle. According to two companion studies co-authored by Stanford University in the US and Beihang University in China, microorganisms in the worms' guts biodegrade the plastic in the process. The papers, published in Environmental Science and Technology, are the first to provide detailed evidence. Understanding how bacteria within mealworms carry out this feat could potentially enable new options for safe management of plastic waste. In the laboratory, 100 mealworms ate between 34 and 39 mg of Styrofoam/day. The worms converted about half of the Styrofoam into carbon dioxide, as they would with
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MARCH / APRIL 2016
Mealworms make Styrofoam plastics their meal
any food source. Within 24 hours, they excreted the bulk of the remaining plastic as biodegraded fragments that look similar to tiny rabbit droppings. The mealworms were said to be as healthy as those eating a normal diet, say the studies, and their waste appeared to be safe to use as soil for crops. Researchers have shown in earlier research that waxworms, the larvae of Indian mealmoths, have microorganisms in their guts that can biodegrade polyethylene (PE). The new research on mealworms is significant, however, because Styrofoam is more problematic for the environment. Meanwhile, the researchers plan to study whether microorganisms within mealworms and other insects can biodegrade polypropylene (PP), microbeads and bioplastics. As part of a "cradle-to-cradle" approach, the researchers will explore the fate of these materials when consumed by small animals, which are, in turn, consumed by other animals. Another area of research could involve searching for a marine equivalent of the mealworm to digest plastic waste in the ocean, which is also a big problem. Meanwhile in 2004, scientists Kevin O’Connor and Patrick Ward of the Department of Industrial Microbiology at the University College Dublin discovered a styrene-eating bacteria strain, Pseudomonas putida CA-3, a common soil microbe. This bacterium has proved capable of turning the styrene into tiny granules of a biodegradable form of plastic called PHA (polyhydroxalkanoate), which can be degraded in the environment. PHA has a broad range of applications, including medical applications such as wound management, drug delivery, and tissue engineering.