plastic
- Dec 28, 2018 -

biodegradable


"The rapid biodegradation of plastics in the intestinal tract of mealworms reveals a new fate of plastic waste discarded in the environment." Beijing university of aeronautics and astronautics professor Yang jun said.



Plastic is difficult to degrade naturally in the environment, and polystyrene is one of the most, because of high molecular weight and high stability, it is generally believed that microorganisms can not degrade polystyrene plastic. In 2015, professor Yang jun's research group of Beijing university of aeronautics and astronautics and Dr. Zhao jiao of shenzhen bgi jointly published two sister research papers in EnvironmentalScience&Technology, an authoritative journal of environmental discipline, which proved that larvae of mealworms (mealworms) can degrade polystyrene, which is the most difficult plastic to be degraded.



The study showed that polystyrene foam as the only food source, yellow mealworms larvae can survive for more than a month, and finally develop into adults, the polystyrene eaten by them is completely degraded into CO2 or assimilated into insect body fat. The findings provide insights into the global problem of plastic pollution.



Folding world puzzle


The pollution of plastic waste produced by petrochemical industry is a worldwide environmental problem. Most plastics are discarded after they are consumed once. So far, the academic circles believe that plastic products may not be decomposed in the natural environment for decades to hundreds of years due to their stable physical and chemical structure.



Professor Yang jun introduced that in 2013, the global consumption of 299 million tons of plastic, of which polystyrene plastic accounted for 7%, annual consumption of about 21 million tons, common plastic lunch boxes, coffee cups and other materials that can withstand the temperature of boiling water is polystyrene. Authoritative investigations have shown that polystyrene, a plastic, can degrade within 0.01-3% of the microbial community in soil, sludge, decaying garbage, or manure within four months.



Every year, there are 40 million tons of waste plastics accumulated in the environment all over the world, and about 2 million tons of waste plastics are thrown into the environment in China every year. Take agricultural film for example, the annual output of agricultural film in China is up to one million tons, and the annual growth rate of 10%, no matter what crops are covered, all mulched soil has residual film. According to statistics, the annual residual amount of agricultural film in China is as high as 350,000 tons, with the residual film rate reaching 42%. A large amount of residual film is left in the tillage layer of farmland of 0-30 cm. That is to say, nearly half of the agricultural film residues in the soil, food safety is a great hidden danger.



"It may take 200 to 400 years for plastics to be completely assimilated into the soil by microorganisms and degraded into CO2 and water for inorganic mineralization, resulting in accumulation in the environment." Professor Yang jun told yangcheng evening news.



Help fold bugs


Yang's team began studying biodegradation of plastics in 2005. Mainly focus on the most difficult degradation of polystyrene and other plastic degradation.



Scientists have previously used soil invertebrates such as earthworms, millipedes, slugs and snails to see if they can eat plastic. When 14C labeled plastics such as PVC, PE and PP were fed, the results showed that they could not be degraded.



Yang jun believes that the idea of biodegradable plastics should be expanded, not limited to microorganisms. Lepidoptera insects and termites can be considered. Marine boaters and drilling mussels can corrode polyethylene and submarine cables.



A 2014 study by Yang jun's team found that wax worms (larvae of Indian valley borer) can chew and eat polyethylene PE film, and the larvae 'intestines were isolated to degrade two strains of PE film, namely, enterobacterium YT1 and bacillus YP1. The team then discovered that the mealworms larva is a more plastic eating animal, larger in size than wax worms (usually 35 mm long and 3 mm wide) and can use styrofoam as its sole food. Yellow mealworms have four stages of life: egg, larva, pupa and adult.



Mealworms, also known as mealworms, belong to coleoptera, coleoptera, mealopteridae, mealopteris (mealopteris). Native to North America, it was introduced into China by the Soviet union in the 1950s. Its dry product contains adipose 30%, contain protein to be as high as 50% above, still contain a variety of elements such as phosphor, potassium, iron in addition. The dried yellow mealworm larvae contained about 40% protein, pupae 57% protein, and adult worms 60% protein.



In China, yellow mealworms are actually similar to silkworms. People can eat them directly, fry them, or use them as fodder. Scorpions, centipedes, clams, snakes, tropical fish and goldfish fed by yellow mealworms not only grow fast and have a high survival rate, but also have strong disease resistance and greatly improved fertility. Breeding yellow mealworms is very easy, farmers can use fresh oats, wheat bran, apple farming.



Folding bugs eats plastic


Professor Yang's team purchased polystyrene plastics from sinopec's yanshan branch without additives or catalysts. Samples of polystyrene plastic labeled alpha 13C and beta 13C are purchased from the United States. Yellow mealworms are purchased from insect farms in daxing, Beijing, and qinhuangdao, hebei province, and raised on grain. These insects are 3-4 years old (that is, they lose their skins 3-4 times).



The yellow mealworms are placed in a polypropylene plastic container with foam blocks. The experimenter regularly measuring eaten by yellow powder insect foam piece weight, control group is yellow powder insect raised in wheat bran, conventional experiment 500 yellow powder insect with 5.8 grams of bubble is the only food, in the control condition of the greenhouse kept separately (25 + 1 ° C, 80 + / - 2% humidity, and the lords of light/dark cycles). During incubation, the dead yellow mealworms are immediately removed.



In the experiment, Yang jun et al. fed yellow mealworm larvae with foam plastic as a single food source. Compared to normal (feed bran) and gastric disorder larvae, it was found that 16 days in the experimental period, the larva dry weight while not as normal feeding larvae significantly increased (+ 33.6%), only a small amount has increased 0.2% (this is because compared with bran, foam plastic water content and low nutrition value), but also not like larva dry weight of gastric disorder significantly (24.9%), and compare the survival rate of larvae feeding of plastic and bran in the two groups, there is no obvious difference.



100 yellow mealworms can consume 34 to 39 milligrams of styrofoam per day. During the 16-day experiment, 47.7% of the foamed plastic consumed by the worms was converted into CO2. The remaining biodegradable particles (about 49.2%) were converted into rabbit feces and excreted out of the body. Tests using polystyrene plastics labeled alpha 13C or beta 13C demonstrate that they are mineralized into carbon-13 labeled carbon dioxide and lipids. The polystyrene foam in the intestinal tract of larvae will degrade within 24 hours.



Larvae that use polystyrene foam as their only food develop into crustaceans, just as healthy worms fed a normal diet (wheat bran) do after a month. The yellow mealworms ate holes in the foam. After passing through the worms' intestines, the chemical structure and composition of the plastic foam ingested change. GPC and c-13 NMR spectra and tg ftir spectra were used to confirm that the long chain polystyrene molecules in the intestinal tract of larvae were broken to form insect metabolites and excreted in feces.



Furthermore, the polystyrene degradable bacteria YT2(exiguobacteriumsp.yt2) was successfully isolated from the intestinal tract of larvae using polystyrene as the sole carbon source. The strain has been preserved in the general microbiological center and national gene bank of China microbial species preservation and management committee, and is the first polystyrene degrading bacteria that has been reported to be preserved in the center internationally.



Folding can eat all plastic


The research team proposed the mechanism of polystyrene degradation by rodent feeding of yellow powder larvae. First, the foamed plastic was chewed into small pieces by yellow powder larvae and ingested into the intestinal tract. In the second step, the chewing action increases the contact area between polystyrene foam and microorganisms and extracellular enzymes. The ingested fragments are further depolymerized into small molecular products under the action of extracellular enzymes secreted by intestinal microorganisms. In the third step, these small molecular products are further degraded and assimilated to form the larva's own tissues under the action of various enzymatic bacteria and the larva's own enzymes. Step 4: the residual foam fragments and some degradation intermediates are mixed with some intestinal microorganisms to be excreted out of the body in the form of insect feces. The foam plastics may be further degraded in the insect feces.