We have often heard of biodegradable materials. Can you recollect a few places where you may come across this word? You may have seen this printed on milk cartons, or on a paper bag used for shopping. You may also have noted how your mother segregates waste based on whether it is biodegradable or not. So what are biodegradable materials?

Let us do an activity to know more about biodegradable materials.

Collect waste from your house for one full day. Do not segregate the waste. What kind of waste are you likely to receive? Kitchen waste like leftover food, vegetable and fruit peels, waste paper, packaging, glass, metal cans and plastic are some of the wastes commonly generated in our houses. Bury this waste in your backyard. If you do not have a garden, you can store the waste in a bucket and cover it with about 15 cm of mud. Check on this waste once every few days. What will you observe?
You will note that the kitchen waste (vegetable peels, fruits peels, residual food) degrades within a few days into compost. Waste like newspapers and packaging made of paper degrade next, and glass and plastic do not degrade at all. In fact, plastics can last in the environment for thousands of years.

So why does kitchen waste degrade so quickly? In the chapter on human nutrition, we had learned about enzymes. Enzymes are proteins that catalyse the breakdown of food within the digestive tract. Bacteria in the soil produce similar proteins that break down the kitchen waste to produce compost. The compost is an excellent source of nutrients for plants and using it in the garden can improve yields. Biogas plants produce methane and compost using the?same principle.The enzymes can also act on paper. However, cellulose, the main component of paper takes a longer time to break down, therefore, paper and paper products stay in the environment longer. Enzymes have no action on plastic and metals. Therefore, these items are not degraded by the enzymes.

Therefore, substances that are degradable by biological means are biodegradable materials.Non-biodegradable materials like plastic and glass are not degraded by natural means. Hence, they can persist in the environment for thousands of years. Can you now imagine what would happen if we keep using plastic indiscriminately? All the plastic will stay on earth for thousands for many years and cause immense environmental damage. See this video below to get an idea of the risk posed by plastic to animals and environment, in general.

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