We are in the age of plastics. If you thought this convenient and ubiquitous killer of humanity began in 1967 when Ben Braddock was given the advice “plastics” in The Graduate you wouldn’t be far off. The first synthetic plastic material was patented in 1856 but mass production of plastics did not begin until after World War II.
Plastics are polymers. Polymers are large molecules made up of many small units linked together. Poly means many and mer means part. Polyethylene plastics are many ethylene molecules linked together. That ethylene molecule, called a monomer - mono = one, mer still means part, is derived from fossil fuels.
There are, of course, many types of plastic; polyethylene, polyurethane, polyester, polypropylene; and more commonly known names like Formica (a phenolic), Nylon (a thermoplastic), and silicone (a polysiloxane). This is just a short list of plastics. They break down, slowly, into tiny/micro particles, or tiny threads in the case of Nylon. These tiny bits have been found in fish, shellfish and even the water we drink. The word microplastics is now used for these very tiny particles. We have these microplastics inside us, lots of them. A few years ago there was a move to produce more ‘biodegradable” plastics. For example, if the plastic was made with starch molecules that connected the polymer molecules then the plastic would breakdown more quickly when the starch was consumed by microbes. Does this help or does this just speed up the process of these tiny plastic particles being passed up the food chain to us? Probably the later.
But…
Where would we be without plastics? Many of us would be dead. I tend to joke in writing - or attempt to - so let me point out, I’m not kidding. Without plastics many of use would be dead. There may be many reasons for this but let me just mention one, syringes used in medicine were once glass. Now they are plastics - used once. How many infections have plastics prevented? There are of course other life saving plastics - bullet-proof vest, car safety features - but I detract from where I wanted this to go. I wanted to explain the idea that we might be able to break down plastics much faster, preventing this lifesaving advance from killing us.
My attention was brought to the idea that some organisms can breakdown plastics, and not just the “biodegradable” types, by a short article in Current Biology (Bombelli and colleagues 2017), where the authors, apparently accidentally, figured out that wax worms were eating holes in plastic bags. In another article in June of this year (Khan and colleagues 2017) a fungus was observed breaking down some plastics. The fungus “Aspergillus tubiengensis was isolated, identified, and found to degrade polyurethane”.
Turns out that this is not new information. A quick search dug up another paper (2014) on the wax worms ability to degrade plastics. It seems Yang et al (2014) scooped Bombelli by three years. Another paper in 2013 is titled, New insights into polyurethane biodegradation and realistic prospects for the development of a sustainable waste recycling process. The NEW in the title suggests that there were old insights. This seems this was a whole field I was unaware of, though not exactly an ancient one. The earliest article I could find in a quick search was from 1991 and by 2002 there was a review article on the subject. What organisms break down plastics? Wax worms, at least two species of fungus, bacteria (maybe all organisms that do so do it in conjunction with bacteria). There is much more out there to read, however, so don’t think this is an exhaustive list.
Are these organisms the saving grace for humanity? Do these organisms break down plastics into materials that can be used by other organisms - for example humus that plants can use? Or does this breakdown just give us more microplastics just waiting to invade our bodies? These questions seems to be unanswered.
Summary:
The good news:
Larvae Wax Moth, Wax worms (Galleria mellonella) - or their gut bacteria, break down some plastics. The fungi (Aspergillus tubingensis, Aspergillus japonicus) break down some plastics.
Plastics we produce may not take 400+ years to degrade.
The Bad News:
Only some plastic types are degraded (polyethylene, polyurethane): Researchers have tested at least eight other polymer plastics that failed to be degraded.
Wax Worms breakdown the plastics to an antifreeze like substance, which is toxic and therefore may not be of much benefit. However, this substance does break down more quickly than the plastic.
Should we alter our plastic production so plastics that degrade slowly (or can’t be biodegraded) are produced only when absolutely necessary - YES.
Can I do this in my backyard next to my compost bin?
Beats the heck out of me. Wax worms are easy to keep and breed but they do like warm temperatures so an outside bin may not work well in the winter. But please try and get back to me.
Do any of these organisms breakdown plastics to the extend that the left over materials are usable by other organism? Unsure, but so far it doesn’t seem so, at least initially. But common sense would suggest that if you break things down - even to nasty micro particles, those particles will degrade faster due to their size (surface to volume ratio). Micro particles, dangerous as they are, are at least one step further along the complete degradation process.
Quick review of surface to volume ratio: 1. Things happen on the surface of cells (or micro particles). 2. the smaller the particle the more surface area per volume. Thus if the particle is large there is less surface for microbes to grab onto and break it down.
Further reading:
http://plastiquarian.com
Bombelli et al 2017. Polyethylene bio-degradation by caterpillars of the wax moth Galleria mellonella. Current Biology 27: R292-R293.
Khan et al 2017. Biodegradation of polyester polyurethane by Aspergillus tubingenesis. Environmental Pollution 225: 469-480.
Yang et al 2014. Evidence of Polethylene Biodegradation by Bacterial Starins from guts of Plastic-eating waxworks. Environmental Science and Technology 48: 13776-13784.
Cregut et al 2013. New insights into polyurethane biodegradation and realistic prospects for the development of a sustainable waste recycling process. Biotechnology Advances 31 (8): 1634 - 1647.
Russell et al 2011. Biodegradation of Polyester Polyurethane by Endophytic Fungus. Applied and Environmental Microbiology 77: 6076-6084.
Kathiresan, K 2003. Polythene and Plastics-degrading microbes from the mangrove soil. Revista de Biología Tropical 51: 629-633.