Question
Why are plastics considered harmful to the environment? Distinguish between biodegradable and non-biodegradable materials with examples.
Solution — Step by Step
Most plastics are non-biodegradable — they cannot be broken down by microorganisms (bacteria, fungi) in the soil. This means plastics persist in the environment for hundreds to thousands of years without decomposing.
When buried, they block water seepage and damage soil structure. When in water, they break into microplastics (fragments smaller than 5 mm) that enter food chains and have been detected in fish, birds, and even human blood.
Burning plastics releases toxic gases like HCN (from nylon), dioxins, and furans — highly carcinogenic compounds.
Biodegradable materials are substances that can be broken down by living organisms (bacteria, fungi, other decomposers) into simpler, harmless substances like , water, and organic matter.
Examples: Paper, wood, cotton, food waste, wool, silk, leather, jute.
These materials can be composted and return nutrients to the soil. They complete the natural cycle within weeks to years.
Non-biodegradable materials cannot be decomposed by microorganisms in a reasonable time. They accumulate in the environment.
Examples: Most plastics (polythene, PVC, nylon, polyester), glass, metals, DDT, pesticides.
These persist for:
- Polythene bags: 20–1000 years
- PET bottles: 450 years
- Nylon: 30–40 years (but fibre microplastics persist much longer)
| Feature | Biodegradable | Non-biodegradable |
|---|---|---|
| Decomposition | Yes, by microbes | No, or extremely slow |
| Environmental impact | Low (returns to nature) | High (accumulates, pollutes) |
| Examples | Paper, cotton, food waste | Plastics, glass, metals |
| Disposal | Compost, landfill | Recycling, segregation |
| Soil impact | Enriches soil | Damages soil structure |
Why This Works
The distinction between biodegradable and non-biodegradable comes down to chemical structure. Natural polymers (like cellulose in paper, proteins in wool) have bonds that microbial enzymes can recognise and cleave. Synthetic polymers (like polyethylene — long chains of ) have no such recognisable bonds — microbes haven’t evolved enzymes to break them.
This is a direct result of how plastics are made: they’re designed to be stable, resistant to heat, water, and chemicals. This same stability that makes them useful is exactly what makes them environmental hazards.
Alternative Method — Remember with Categories
Think of origin:
- From nature → usually biodegradable (plants, animals, microbes made it, so microbes can break it down)
- Synthetically made → usually non-biodegradable (humans designed it; microbes have no tools for it)
Exceptions: Some modern bioplastics (PLA, PHA) are synthesised but designed to be biodegradable.
Common Mistake
Saying “plastics are harmful because they are poisonous.” Most plastics are chemically inert and non-toxic in their solid form — the harm comes from their persistence and physical effects (blocking digestive tracts, accumulating in ecosystems), not direct toxicity. The toxicity issue mainly applies to burning plastics or to plastic additives (plasticisers, flame retardants), not the polymer itself.