One tiny mouthful at a time, mealworms are reducing the quantity of discarded polystyrene foam on the planet.
This form of polystyrene – known as extruded polystyrene foam and made from petroleum – is relatively strong while being very light, and is used extensively, from packaging computers and fridges. It’s perhaps best known as the material used to make Styrofoam cups and packaging. It’s commonly found where it shouldn’t be, in rivers or roadside hedges, and it also constitutes a large proportion of landfills as well as ocean dumps.
The problem with extruded polystyrene foam is that it does not biodegrade, and while it can be recycled, this is often uneconomical as it is easier and cheaper to simply make more.
A team of Chinese and American researchers, however, have the larval form of a darkling beetle – better known as mealworms – can eat and degrade Styrofoam.
“Our findings have opened a new door to solve the global plastic problem,” says Wei-Min Wu, a researcher in Stanford University’s department of civil and environmental engineering.
These findings are described in two papers, recently published in the journal Environmental Science and Technology.
A hundred meal worms eat about 35mg of Styrofoam a day, according to Stanford University. That is about the size of a small pill. The worms excreted about half of the Styrofoam as carbon dioxide, and within 24 hours, the worms expelled the remaining polystyrene as biodegraded fragments that resembled tiny rabbit droppings.
“Fed with Styrofoam as the sole diet, the larvae lived as well as those fed with a normal diet (bran) over the period of one month,” the authors – headed up by Yu Yang and Jun Yang from Beihang University in Beijing – write in the first paper.
They found that the bacteria in the mealworms’ guts degraded the polystyrene. These results were detailed in the second paper.
This is not the first time that the Chinese group has identified worm gut bacteria that can break down plastics. They published an article last year that detailed how wax worms could eat polyethylene, which is the most common plastic and used in plastic bottles, among many other things.
However, Ramani Narayan, a professor in the department of chemical engineering and materials science at the Michigan State University, told htxt.africa: “Biodegradability, particularly plastics biodegradability, is a much-used and abused terminology.”
Complete biodegradability “…must show that [approximately] 90% of the product’s carbon is utilised by the micro-organisms present in the selected disposal system”.
“It is interesting that mealworms consume polystyrene and chew on it. However, [the paper] states that more than 50% of the polystyrene eaten by the mealworms [is] being excreted into the environment….[In this instance], the excreted product is still a large polystyrene molecule, and even the authors state that the excreted material is polystyrene,” Narayan says.
“The authors state that the excreted polystyrene will “eventually biodegrade” in the soil environment. This is very misleading as no data is provided.”
Stanford University, in its statement, says that more research is needed to “understand conditions favourable to plastic degradation and the enzymes that break down polymers. This, in turn, could help scientists engineer more powerful enzymes for plastic degradation, and guide manufacturers in the design of polymers that do not accumulate in the environment or the food chain.”[Image – Yu Tan]