UPSC Prelims 2021 Q74: Bisphenol A (BPA) in Plastics — Explained
Bisphenol A (BPA), a cause of concern, is a structural/key component in the manufacture of which of the following kinds of plastics?
- Low-density polyethylene
- Polycarbonate
- Polyethylene terephthalate
- Polyvinyl chloride
Answer: (b) Polycarbonate
Statement-wise explanation
- a: incorrect — Low-density polyethylene is a polyolefin made by polymerising ethylene gas under high pressure. Its chain contains only carbon and hydrogen, with no ring-shaped phenol units, so BPA plays no structural part in it. LDPE is used in carry bags, cling film and squeeze bottles.
- b: correct — Bisphenol A is the main monomer of polycarbonate. Its two phenol rings are joined through carbonate links, traditionally by reacting BPA with phosgene. CSIR-NCL describes BPA as a feedstock for polycarbonate, epoxy resins and other engineering plastics. When India launched a BPA pilot plant in 2022, its estimated demand of about 1,35,000 tonnes a year was entirely imported. Because BPA can leach out of polycarbonate when it is heated, BIS revised the baby feeding bottle standard (IS 14625) in 2015 and dropped polycarbonate as a permitted material.
- c: incorrect — Polyethylene terephthalate (PET) is a polyester made from ethylene glycol and terephthalic acid, as its name suggests. It contains no BPA. PET is the clear plastic in most water and soft-drink bottles and carries resin code 1.
- d: incorrect — Polyvinyl chloride is made by polymerising vinyl chloride monomer. Its main chemical concerns are the vinyl chloride monomer and the phthalate plasticisers added to soften it, not BPA.
How to eliminate
This question is mostly solved by knowing the fact, but the names of the plastics help. 'Bisphenol' means two phenol rings, so look for a plastic built from ring-containing monomers that are not already named. LDPE comes from ethylene and PVC from vinyl chloride. Both are simple chain polymers with no phenol rings, so they can go first. PET's name gives its monomers away: ethylene glycol and terephthalic acid. That leaves polycarbonate. Everyday knowledge points the same way: 'BPA-free' labels appear on hard, clear, reusable bottles and baby bottles, which were traditionally made of polycarbonate. Fact to remember: BPA is the building block of polycarbonate plastics and epoxy resins, such as the inner linings of food cans.
Know more
Bisphenol A (BPA) is an industrial chemical made from phenol and acetone. Its molecule has two phenol rings. It is used mainly to make:
- Polycarbonate: a hard, transparent, shatter-resistant plastic used in reusable bottles, food containers, CDs/DVDs, safety goggles and lenses.
- Epoxy resins: coatings inside food and beverage cans, and in adhesives and paints.
- It is also used in some thermal-paper receipts.
Why it is a concern: BPA is an endocrine-disrupting chemical (EDC). It mimics the hormone oestrogen. It can leach from polycarbonate and epoxy linings into food, especially with heat, repeated washing or acidic contents. Infants are the most vulnerable group. In 2015, BIS revised IS 14625 (plastic feeding bottles) and dropped polycarbonate as a permitted material. A further revision in draft in 2026 proposes an outright ban on BPA. The EU's Regulation (EU) 2024/3190 restricts BPA in food-contact materials.
Common plastics and their building blocks
| Plastic | Monomer(s) | Resin code | Typical use | Main chemical concern |
|---|---|---|---|---|
| PET | Ethylene glycol + terephthalic acid | 1 | Water/soda bottles | Reuse, heat exposure |
| HDPE | Ethylene | 2 | Milk jugs, pipes | Low |
| PVC | Vinyl chloride | 3 | Pipes, cables, flooring | Phthalates, vinyl chloride, dioxins on burning |
| LDPE | Ethylene | 4 | Carry bags, films | Low |
| PP | Propylene | 5 | Containers, BPA-free bottles | Low |
| PS | Styrene | 6 | Thermocol, cups | Styrene |
| Polycarbonate | BPA (+ phosgene/carbonate) | 7 (Other) | Hard clear bottles, lenses | BPA leaching |
Related analogues: BPS and BPF are often used in 'BPA-free' products. Studies show they have similar hormone-like effects, so 'BPA-free' does not automatically mean safe.