UPSC Prelims 2021 Q25: Magnetite Pollution Sources — Explained
Magnetite particles, suspected to cause neurodegenerative problems, are generated as environmental pollutants from which of the following?
1. Brakes of motor vehicles
2. Engines of motor vehicles
3. Microwave stoves within homes
4. Power plants
5. Telephone lines
Select the correct answer using the code given below.
- 1, 2, 3 and 5 only
- 1, 2 and 4 only
- 3, 4 and 5 only
- 1, 2, 3, 4 and 5
Answer: (b) 1, 2 and 4 only
Statement-wise explanation
- 1: correct — Braking heats the pads and discs by friction. That heat produces tiny iron-oxide spheres, including magnetite. The 2016 PNAS study by Barbara Maher and colleagues found magnetite nanoparticles in human brain tissue and named brake-pad friction as one source of high-temperature magnetite. Later roadside studies (Gonet et al., 2021) found brake wear to be the main source of airborne magnetite at the sites they tested.
- 2: correct — Burning fuel in vehicle engines, especially diesel engines, gives off magnetite nanoparticles in the exhaust. The 2016 study said the rounded, fused particles it found in the brain point to high-temperature combustion of this kind. It named vehicle engines as a likely source.
- 3: incorrect — A microwave oven heats food with non-ionising radiation. It does not burn fuel, and it has no rubbing surfaces that throw off iron particles. The indoor sources the researchers named were open fires and poorly sealed cooking or heating stoves, not microwave ovens.
- 4: correct — Coal-fired power plants burn fuel at high temperature, and their fly ash contains iron-rich spheres. The 2016 PNAS paper compared the brain particles with fused magnetite spheres from a coal power station (Didcot, UK). It treated industrial combustion as a source alongside vehicles.
- 5: incorrect — Telephone lines carry weak signals along wires. Nothing burns in them and nothing is ground down by friction, so they release no particles. Magnetite pollution comes from combustion or frictional heating, and telephone lines involve neither.
How to eliminate
Ask one question of each item: does it involve high-temperature burning or friction? Magnetite pollution forms only that way. Brakes (friction), engines (combustion) and power plants (combustion) pass the test. Microwave ovens and telephone lines involve no burning or grinding, so they fail. Option structure helps too. Rejecting telephone lines alone leaves only the option that has neither microwaves nor telephone lines. Rejecting microwaves alone removes three options. The trap is the word 'magnetic'. Microwaves and telephone lines sound electromagnetic, but magnetite is a mineral, an iron oxide. It enters the air as particles, not as a field. Fact to remember: airborne magnetite nanoparticles come from combustion and friction, mainly vehicle brakes, engines, industrial burning and open fires or stoves.
Know more
Magnetite (Fe₃O₄) is a strongly magnetic iron oxide. It forms naturally in rocks, and some is made inside living bodies. In polluted air, most of it comes from human activity, as tiny particles called nanoparticles (less than 0.1 µm, or 100 nm, across).
How it forms: Iron in fuel, engine parts or brake pads gets very hot, melts and solidifies again as tiny round spheres. Magnetite made naturally in the body forms angular crystals instead. That shape difference is how scientists tell the two apart.
The 2016 brain study (Maher et al., PNAS): Researchers examined brain tissue from 37 people aged 3–92 in Mexico City and Manchester. They found millions of magnetite particles per gram of tissue. Most were rounded spheres up to about 150 nm across, which marks them as pollution, not natural. Particles smaller than about 200 nm can travel from the nose into the brain along the olfactory nerve.
Why it is linked to the brain: Magnetite can help produce reactive oxygen species (free radicals), which are linked to neurodegenerative diseases such as Alzheimer's. The link is suspected, not proven. That is why the question says "suspected".
| Source | How magnetite forms |
|---|---|
| Vehicle brakes | Friction heats pads and discs |
| Vehicle engines (esp. diesel) | Fuel burning, in the exhaust |
| Coal power plants, industry | Burning coal, in the fly ash |
| Open fires, leaky stoves | Burning biomass indoors |
| Underground rail | Wheel–rail and brake friction |
Non-exhaust emissions: Fumes from vehicle exhaust are controlled in India by Bharat Stage (BS) emission norms. Particles from brakes, tyres and road dust are not. As engines get cleaner, these non-exhaust sources make up a growing share of traffic particulate matter (PM).
In the news
The 2016 PNAS study that found pollution magnetite in human brains got wide press coverage. In 2021, new research named vehicle brake wear as the main roadside source of airborne magnetite. These studies made brake and engine particles a current topic in the run-up to the 2021 exam.
NCERT Concepts to Revise
- Particulate matter: Magnetite pollution consists of ultrafine particulate matter; particle size decides whether it can reach the brain through the nose.
- Air pollution: The question asks which everyday sources add magnetite to air pollution; knowing the main sources of air pollution frames each statement.
- Fly ash: Statement 4 depends on whether burning coal in power plants leaves iron-rich particles in its ash.