UPSC Prelims 2024 Q17: PFAS 'Forever Chemicals' — Explained
With reference to perfluoroalkyl and polyfluoroalkyl substances (PFAS) that are used in making many consumer products, consider the following statements:
1. PFAS are found to be widespread in drinking water, food and food packaging materials.
2. PFAS are not easily degraded in the environment.
3. Persistent exposure to PFAS can lead to bioaccumulation in animal bodies.
Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Answer: (d) 1, 2 and 3
Statement-wise explanation
- 1: correct — PFAS have been found in drinking water, in food and in food-contact materials such as grease-proof paper, fast-food wrappers and microwave popcorn bags. In April 2024 the US Environmental Protection Agency (EPA) set its first national drinking-water limits for six PFAS. The limits for PFOA and PFOS were 4 parts per trillion each, and the EPA estimated the rule would cut exposure for about 100 million people. Studies of foods also report PFAS in fish, eggs, meat and dairy, often moving into food from packaging and from contaminated water and soil.
- 2: correct — PFAS contain many carbon–fluorine bonds, one of the strongest bonds in organic chemistry. Sunlight, water and microbes cannot easily break them. This is why PFAS are called 'forever chemicals'. Their persistence is the reason three PFAS groups are listed as Persistent Organic Pollutants under the Stockholm Convention: PFOS in 2009, PFOA in 2019 and PFHxS in 2022.
- 3: correct — Most POPs build up in fat. Many PFAS instead bind to proteins in blood, liver and kidney. Because the body clears them slowly, repeated exposure makes them bioaccumulate, and some PFAS biomagnify up food chains, for example in fish and in animals that eat fish. Bioaccumulation is one of the four criteria the Stockholm Convention uses to list a chemical as a POP, so the listed PFAS meet it by definition.
How to eliminate
Option structure helps here. All three statements describe the standard 'forever chemicals' profile. The words 'not easily degraded' (Statement 2) are almost a definition of 'forever chemical', so if you had read even one news item on PFAS you could mark Statement 2 correct. That removes the option that leaves out 2 (1 and 3 only). Next, a chemical that resists breakdown and is taken in again and again will tend to build up in living bodies. That makes Statement 3 a natural consequence of Statement 2 and removes '1 and 2 only'. The stem says PFAS are 'used in making many consumer products', which points to wide human exposure through water, food and packaging, so Statement 1 is consistent with it. None of the statements uses an absolute word such as 'only', 'always' or 'all'. Soft, descriptive statements in a current-affairs science question are usually true. The fact to remember: PFAS = persistent + bioaccumulative + widespread, and that profile is why they are called forever chemicals.
Know more
What PFAS are. Per- and polyfluoroalkyl substances are a family of thousands of synthetic chemicals. The OECD (2021) definition counts any fluorinated substance with at least one fully fluorinated methyl (–CF₃) or methylene (–CF₂–) carbon atom. Perfluoroalkyl means every hydrogen on the carbon chain has been replaced by fluorine. Polyfluoroalkyl means only some have.
Why industry uses them. The C–F bond makes PFAS repel both water and oil and resist heat. Common uses:
| Use | Examples |
|---|---|
| Non-stick coatings | PTFE (Teflon) cookware |
| Food-contact materials | Grease-proof wrappers, pizza boxes, popcorn bags |
| Textiles | Stain-proof carpets, waterproof jackets |
| Firefighting | Aqueous film-forming foam (AFFF) |
| Others | Cosmetics, paints, electronics, lubricants |
Why they are a problem.
- Persistence: they barely break down, so they stay in soil and water for decades.
- Mobility: many dissolve in water and travel through groundwater and rivers.
- Bioaccumulation: they bind to blood proteins and stay in the body for years.
- Toxicity: in November 2023 the WHO's cancer agency IARC classified PFOA as carcinogenic to humans (Group 1) and PFOS as possibly carcinogenic (Group 2B).
Global regulation.
| Instrument | PFAS covered |
|---|---|
| Stockholm Convention on POPs | PFOS (Annex B, 2009); PFOA (Annex A, 2019); PFHxS (Annex A, 2022) |
| US EPA drinking-water rule (Apr 2024) | Six PFAS. PFOA and PFOS capped at 4 parts per trillion |
The Stockholm Convention targets chemicals that are persistent, bioaccumulative, toxic and able to travel long distances. Annex A means elimination. Annex B means restriction.
In the news
Several PFAS developments came in the months before the June 2024 exam. In November 2023 IARC classified PFOA as a Group 1 human carcinogen. In April 2024 the US EPA set its first national drinking-water limits for PFAS. Around the same time, the EU discussed a broad restriction on the whole PFAS family.