Are Nanoparticles a Health Hazard?

here is a new industrial revolution taking place all around us. The only problem is we can’t see it.
The building blocks, being developed at the cost of billions of dollars by scientists, governments and multinational corporations, are just a few atoms or molecules thick — nanoparticles. Many are less than 100 nanometres (nm) — one-billionth of a metre — thick. A single human red blood cell in comparison is around 500 nm in diametre.

It’s a pity though that our eyesight isn’t good enough at nanometre level, for if it were, we would see that nanoparticles of precious metals like gold, silver and titanium have already made the jump from research labs to our homes. Manufactured nanoparticles are today present in thousands of consumer products around the world — silver in washing machines and water purifiers to kill bacteria, zinc in cosmetics to protect against ultraviolet rays, carbon nano-tubes in tennis rackets to make them stronger and lighter, titanium in household paints to decompose dust and grime without human intervention.

Nano is the New Black
“There’s Plenty of Room at the Bottom”
So went the classic lecture by the Nobel prize-winning physicist Richard Feynman in 1959 that many nano-ficionados now consider the conceptual sun of the nanotechnology universe. “Why cannot we write the entire 24 volumes of the Encyclopedia Britannica on the head of a pin?” he asked.

“Because there isn’t much of a point, or money, in doing so!” is the answer he would have got today from nanotechnology researchers. Instead their time is mostly spent figuring out newer properties for nanoparticles which can then be embedded into commercial applications.

Nanoparticles are highly reactive and prone to unusual properties. Describing gold, a metal that is normally inert to all other chemicals, Prof. C.N.R Rao, Honorary President and Linus Pauling Professor at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) and the head of its Nanoscience centre, says “At 200-300 nm thickness, gold is not metallic, it does not shine — in fact it is not gold. And at 1.5-2 nm, it reacts like mad!”

Gold that is not gold when shrunk to nanometer size might sound like an absurdity to many, but it’s exactly this change in physical properties that make nanoparticles popular.

For example zinc oxide (ZnO) and titanium dioxide (TiO2) have been used as active ingredients in sunscreens for decades because of their ability to absorb ultraviolet rays and reflect back much of the other remaining sunlight. But they are both white — the reason many sunscreens leave a white residue on the face. When shrunk to nanometre size however, they become transparent without losing their light reflecting or absorbing abilities.

Silver, an ornamental metal and a powerful bactericide, can be reduced to nanoparticle form to destroy disease-causing bacteria from all kinds of places — kitchen counters, contaminated water, dirty clothes and stinky underarms.

Samsung claims its Silver Nano range of washing machines release hundreds of billions of silver nano-ions with each wash to kill over 99 percent of the bacteria found in dirty clothes, while the same technology when lined on the doors of their refrigerators kill bacteria that could spoil stored food. Eureka Forbes’ water purifiers use nanosilver-coated filters, developed by Prof. Pradeep, head of IIT-Madras’ Nanoscience department, to destroy harmful bacteria from drinking water. Swach, the mass-market water filter introduced by the Tata Group, also uses nanosilver (coated on rice husk particles) to purify drinking water. During the last flu pandemic threat authorities in Hong-Kong sprayed subways with nanosilver to disinfect them.

L’Oreal, the world’s largest cosmetics company, reportedly spends over $600 million each year researching and patenting nanoparticles. The head of its nanotechnology unit also sits on the management board.

Therefore a metal that is a poor second cousin to gold in a world where we value yellow over white, is the undisputed metal of choice in the nanoparticle world. In fact, silver is more popular than any other material, according to the database of consumer products using nanoparticles maintained by the Woodrow Wilson International Center for Scholars.

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