#70 - August 2023 - Garden Stuff - © Sandy Lang - slang@xtra.co.nz
PLASTICSAugust/September: Early spring, days lengthen, clocks change, buds swell, tiny leaves. Warming up but late frosts till Labour Day.The plastocene: Welcome to the new geological age. Plastics are now in the sedimentary record. Since 1950 we’ve created about 10 billion tons of the stuff and less than 10% has been recycled. Plastics are causing terrible problems in the biosphere – not just the big bits but the microscopic bits too. Tiny plastic particles are turning up in our food and water, and so becoming part of us.What is plastic? Chemists define a plastic as a large number of small carbon molecules (monomers) joined together to form a long chain (polymer). This definition fits well with polythene (think plastic bags) - a long chain of many thousands of ethene (C₂H₄) molecules, and with cellulose (think plant cell walls) - a long chain of many thousands of glucose (C₆H₁₂O₆) molecules. So, you’re wrong if you think plastics are new. Amounts: Polythene is the most common synthetic plastic (34% of the total - mostly packaging) and cellulose is the most common bioplastic (50% of all wood). About the only difference between these is cellulose has been around billions of years while polythene has been around only since 1898. Microbes have evolved to break cellulose down, but not yet for polythene.Biodegradation: The good thing about most synthetic plastics is they’re not biodegradable - you can use them where you don’t want them to degrade (sheathing on buried cables, waterpipes). This is also the bad thing (old plastic bags/bottles, old fishing nets, ropes).Smart polymers: Nature is pretty clever with its bioplastics. There’re used for... •Structure: Cellulose – cell walls, wood (plants), Chitin – exoskeleton (insects), Keratin – skin, wool, feathers (animals). •Energy stores: Starch (plants), Glycogen (animals). •Databases: DNA (plants, animals). •Biochemistry: Enzymes - catalytic proteins (plants, animals). •Springs: Elastin - stretchy stuff in skin (animals). •Motility: Actin, Myosin - contractile filaments in muscles (animals). •Electrical insulation: Myelin - around nerves (animals). •Waterproofing: Cutin - around all external cells (plants).Biodegradable plastics: Industry is racing (too slowly) to replace its non-biodegradable synthetic plastics with biodegradable ones. And microbes are racing (more slowly) to find ways to degrade the huge amounts of waste plastic now cluttering the biosphere. But when they do, it will be the end of plastic waterpipes and cable sheathing too...!___________________________________