Microplastics

Picture it. A mountain stream bathed in the yellow light of the summer sun, surrounded by native forest. Children screaming in the cold water, splashing each other, and floating through the rapids from one pool to another. They’re draped across a little white raft fondly named “Scruffy”, a haphazard shaped piece of white polystyrene and a very effective floating aid for small children such as these.


At first thought, it sounds idyllic. But one thing I distinctly remember about Scruffy the raft was the seemingly endless streams of white polystyrene balls that would rub off (sometimes quite destructively when a rock was intercepted at speed) into the river as we would squeak our way through the bracing water.


Scruffy, the source of endless fun and pollution

Now, decades later, these memories were stirred when Australia’s popular newspapers published a piece on the impact of contaminants called microbeads on the environment. Microbeads are a form of another well-known type of plastic rubbish called microplastics. Although plastic rubbish is not pleasing to see in any form, microplastics are a problem not just because they visually mar the landscape.


The effect of microplastics is actually more insidious than plastic rubbish in its larger form due to their small size and the physical and chemical reactions which result from this size.


A study of microplastics was undertaken in marine waters off the eastern coast of the United States of America all the way back in the 1970s. The study found substantial microplastic pollution, mostly in the form of polyethylene, polystyrene, and styrofoam, with some other miscellaneous hard and soft plastics. These plastics were thought to originate from ships dumping rubbish at sea and from poor pollution control by plastics factories on the mainland.


Decades later, a study in the marine waters up and down the East Coast of Australia and on the coast of South Australia also found abundant microplastic pollution. These microplastics were mostly hard plastics made of polyolefins (polyethylene and polypropylene). Microplastics to the east of the Australian mainland originated from domestic rubbish within Australia. Plastic refuse collected in Tasmania and South Australia instead drifted there from across the Southern Hemisphere and had a variety of domestic and marine pollution sources.


The microplastics in the Australian study ended up in the food chain. Small organisms ingested the plastic, or became entangled in it, before being consumed in turn by larger animals. This process not only introduces the potential contaminants/toxins within the plastics to the foodchain, but can cause increasing contaminant/toxin concentrations with each step up through the ecosystem in a process called biomagnification.


Microplastics are also concerning because of the substances they are made from. Plastics are polymers, made by joining a number of smaller chemicals (monomers) together to form a larger one. More than 50% of the monomersused to create well known plastics such as polyvinyl chloride, polycarbonate, polyurethane and polystyrene are toxic. While combining monomers into polymer form decreases their toxicity, solvents (e.g. benzene, cyclohexane), additives (e.g. phthalates, tributylin), and unreacted monomers (e.g. styrene) all occur in plastic after it is made.


These chemicals are then available to migrate out of the plastic, and in the case of microplastics, into the bodies of the aquatic organisms which ingest them.


Some microplastics, such as polyethylene and polypropylene, are also hazardous due to other toxic chemicals adsorbing to them. The concentrations of these adsorbed chemicals are sometimes orders of magnitude greater than seen in other well known toxic chemical sinks like sediments and soils. Potentially toxic chemicals which are known to adsorb to microplastics include both organic pollutants such as polychlorinated biphenyls and polyaromatic hydrocarbons, as well as inorganic pollutants such as cobalt, nickel, zinc, and lead.


Densities as high as 102,000 microplastic particles per square metre have been measured. Concentrations are also increasing at an alarming rate, and increased by two orders of magnitude between the 1970s and the 1990s.


Not surprisingly, the increasing concentration of microplastics in a marine water body is correlated to the increasing use of plastics within nearby countries, although the case is more complicated in the great oceans of the world. There currents converge in phenomena called gyres, bringing plastics and other debris together to create great floating rubbish dumps.


I wonder where Scuffy’s tiny polystyrene beads of my childhood are now located? Maybe they were safely buried deep beneath sediment, where nothing could adsorb the styrene monomers. Maybe some were ingested by some unwitting fish larvae, chocking some and slowly poisoning others. Or maybe I unwittingly ate some, as part of this increasingly polluted food chain.


There is little good news on the issue of microplastics, apart from an increasing awareness that there is a problem. For now, the microplastics problem is just another one of the great many burdens on the planet’s ecosystem.


All big in their own right, collectively the environmental problems facing the world are indeed daunting. Great changes have happened before. One can only hope they will happen again soon in relation to the environment.

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Canberra, Australia

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Page last updated 10 July 2020

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