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Microplastics and the Environment

2015-12-01

Microplastics are less than 5mm in diameter and are either produced that way or devolve from larger pieces through environmental degradation.   They are ubiquitous but have increased in volume  over the last fifty years because, according to one scientific abstract, “annual plastic production has increased dramatically from 1.5 million tonnes in the 1950s to approximately 280 million tonnes in 2011 (PlasticsEurope, 2012)”

The word “plastic” has two meanings: “soft and easily pliable” or the more common use, which is now essentially shorthand for “synthetic polymer.”    Plastic was preceeded by a compound of nitrocellulose dissolved in ether and alcohol, known as collodion, which replaced the egg white (albumen) used in photographic plates and was also used for medical dressings.  Egg whites were not in limited supply, but as a natural product, it was subject to rapid degradation.

Plastics as such were first produced by  Alexander  Parkes in 1855 and later by John Wesley Hyatt in the United States.   Parkes patented his process but was unable to commercialize it; Hyatt obtained the patent, performed additional experiments, and was able to produce a compound which he made into billiard balls, replacing ivory with celluloid, in 1869.

Hyatt’s replacement was needed because ivory was in limited supply; one set of elephant tusks produced only eight billiard balls.  Other compounds were used, but none were as resilient as celluloid.  A story has circulated that Hyatt won a $10,000 prize offered by a New York company for his invention, but there is no evidence that he actually received the prize (Wikipedia).

In Parkes’ and Hyatt’s  processes, nitrocellulose (from cellulose, a natural polymer of glucose that is found in plant cell walls) is treated with camphor (a natural terpenoid derived from laurel trees or rosemary leaves) to obtain celluloid.  When compressed into a ball, celluloid is neither soft nor pliable, but when stretched out into the thickness of movie film, it is indeed soft, pliable, and readily bent and straightened repeatedly.

When formed into film, celluloid is quite flammable, and when exposed to the heat of a movie projector light it will spontaneously burst into flame at 150 degrees Celsius.  The problem of burning movie film was not solved until celluloid was replaced by acetate in the 1950’s (Wikipedia) and nearly all film produced on celluloid has probably been destroyed, although copies exist.

The first “completely synthetic” plastic, Bakelite, was invented by Leo Baekelite in 1907 as a substitute for shellac in electric insulation.   Again, shellac was in limited supply; it is produced from the secretions of female lac bugs, dissolved in ethanol.  It has been known since ancient times, and was used on furniture since at least the 1200’s.    Shellac has been largely replaced by nitrocellulose lacquers and polyurethane for furniture applications since the 1920’s.  It was used to produce phonograph records at least until the 1950’s, when it was replaced by vinyl.  Shellac is still used as an edible coating on pills, candies, and apples.

Bakelite is made from phenol and formaldehyde with heat and pressure, and is called “thermosetting” because its liquid state turns solid on further heating.   Bakelite was used for thousands of products, from telephone casings to  jewelry.  The base material, phenol, is also used in making nylon, which was invented in 1935 and first used for the bristles in toothbrushes.  Nylon was used for women’s stockings starting in 1940, and for parachutes since WW II.

Phenol is made from petroleum, which is actually a natural product although it is greatly altered from its original state as the bodies of trees and other dead organisms.  These organisms died in catastrophic circumstances which disallowed natural degradation by smaller organisms.  Layers of dead material were covered in volcanic lava or sediment and then subducted to great depths under the earth, where heat and pressure under anoxic conditions transformed them into oil.

Formaldehyde is made from methanol, which is produced commercially from the methane in natural gas, or  by fermentation of sugar cane, corn, or switchgrass.   Methanol was originally produced by the Egyptians for embalming through pyrolysis of wood.   “Natural” gas is, of course, naturally produced in the same fashion as petroleum.

Bacteria that can digest nylon were discovered in 1975 in a waste water pool at a nylon factory.  It is believed that these bacteria had developed an enzyme to break down nylon from new mutations, as the nylon compounds did not exist in nature before nylon was produced in the laboratory.

The problem of microplastics comes from the universal production and use of plastics; originally in many forms, it breaks down into small particles which, if not captured and recycled, are lost into the environment.  Microplastic pellets are produced to be used as abrasives in air-powered sanding guns; pellets are also the starting material for melting into larger aggregates.  As noted, there has been an enormous increase in the production of plastics because they are so useful for so many things.

Microplastics are frequently ingested by small organisms in mistake for their normal food, and appears internally.  They may either be expelled with digestive products, lodge in the digestive system,  or may intrude into the organism’s circulatory system and even into individual cells.  Little is known about the toxicity of microplastics; studies to determine how living organisms tolerate this substance are only beginning.

The possible toxicity of microplastics evokes great concern and speculation as to potential mechanisms of damage to living organisms, but there is little solid information.  There is a Wikipedia article on microplastics which suggests obstruction of the digestive tract, false satiation, and leaching of plastic components like bisphenol-A (BPA), heavy metals (and many other substances that adhere to plastic during its breakdown) as possible mechanisms of toxicity.

I suspect that there will be much more information on microplastic toxicity in the near future because of the enormous increase in the quantity of this material in the environment over the last fifty years and likely continuing increases.  Without hard information, it is difficult to speculate on the degree of toxicity.  Larger pieces of plastic have become lodged in the digestive tracts of birds and fish, strangulated animals (think of the rings that hold beer cans together), trapped cetaceans in their meshes (discarded or lost fishing nets and line)  and caused unsightly accumulations on beaches and on ocean surfaces.

The problem of microplastic pollution can be ameliorated by recycling of used and damaged plastics.  Discarding plastic articles that are no longer useful leads to buildups of resilient but partially degraded pieces of plastic that eventually become microplastics.  These are no longer visible but persist in the environment for many years.  Microplastics will persist until there is widespread evolution of bacteria and eventually larger micro-organisms which can break down plastics into their component molecules, that can then be metabolized.  Creating articles out of cellulose or fungal mycelia (such as experimental packing “peanuts”) will bypass this problem of evolution; this has been tried and is suitable for numerous materials that do not need great structural strength.

An analogous problem (or non-problem) is that natural fibers like cotton and wool also break down into microparticles that appear in fresh water contaminated by the discharge of washing machines.  As far as is known, these tiny particles  do not cause any environmental damage, although they are mentioned in the scientific literature as a “potential” problem.  Concern about microplastics is certainly justified, but I don’t think this problem will approach the dimensions of global warming; recycling durable but broken items and avoiding the use of inherently durable plastics in discardable items are important aspects of harm avoidance.

[Most of the material in this post was obtained thru Wikipedia]

 

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4 Comments leave one →
  1. Richard L Steagall permalink
    2015-12-02 05:20

    This plus the amount of plastic in Pacific Ocean. Why did they stop using glass bottles?

    Sent from my iPhone

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    • 2015-12-02 17:55

      They stopped using glass because it’s heavier for an equal strength, and more expensive to manufacture and transport. A good short term decision, possibly bad long term. Glass bottles are easier to recycle but have been estimated to last a million years in the environment if undisturbed.

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      • 2015-12-02 22:30

        I should have mentioned that plastic is chemically somewhat unstable and spontaneously slowly degrades, while glass is chemically very stable although brittle at room temperature. This factor slightly relieves the burden of microplastics on the environment, and along with the evolution of bacterial and cellular enzymes that degrade plastics and can live off of them, there may be some slight amelioration.

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