楚天指数，大涨长红!

dascarol

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原帖由 dascarol 于 2007-8-23 12:25 发表
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stubor

So what's the problem?

Lead is toxic, and as young children tend to chew things, they are particularly prone to ingesting it. Not good for their vulnerable, developing brains. It was increasingly recognised in the first half of the 20th century that children were being poisoning with lead paint, and its use in cots and toys had been phased out in the West by the 1950s. However, lead-based decorative household paints were still used for another couple of decades before this too ended due to health concerns.

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Why is lead toxic?

Lead can disrupt numerous crucial bodily functions, and hence has a wide variety of symptoms, from vomiting to madness to death. It's known to be a potent blocker of receptors of glutamate, a neurotransmitter crucial for learning. It is also able to displace a series of other metals from doing their normal job in the body - most significantly, calcium, iron and zinc. A particular problem is that lead displaces the zinc from the enzyme delta-aminolaevulinate dehydratase, which is crucial for the biosynthesis of heme, the iron-binding part of the haemoglobin molecule that carries oxygen around the blood. This results in cells around the body being short of oxygen, causing a cascade of associated problems.

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All lead paints have been banned then?

Almost. For the vast majority of uses, lead pigments have been replaced with titanium dioxide, which is so safe it's also used in food colourings as well as in sunscreen. In the EU, lead paint can now only be used for the restoration and maintenance of works of art and historical buildings. In the US, lead paint can be used in limited industrial settings, such as to coat ships hulls.

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How was the toxic paint found?

Mattel identified the toxic paint during routine safety checks. Lead in paint - either in its liquid form, or as a dried coating on a product - can be detected by a number of analytical techniques, said Allan Stewart of testing and certification firm Intertek's Measurement Science Group Lab on Teesside, UK. Atomic absorption and x-ray fluorescence spectroscopy are both general methods that can reveal the presence of lead, while inductively coupled plasma mass spectrometry can detect lead in less than part-per-billion quantities, he added.

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So what's happening in China?

China is gradually cracking down on the use of lead, banning leaded petrol in 2000, for example. However, lead paint is cheaper than the alternatives, which seems to have tempted certain Chinese manufacturers to use it in preference to the non-toxic, and legal, replacements. In response to a series of product safety scandals, which have included toxic pet food and toothpaste, the Chinese government have appointed legendary 'fixer' Wu Yi to the task. Yi, who as vice premier is the most senior female official in the country, will head a new cabinet panel on product safety, in an attempt to address the country's problems with product safety.

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Researchers in Switzerland have built nanoscale cargo loading stations and shuttles, an important step towards assembly lines for nanotechnology.

Drawing of a nano conveyor belt

Biological assembly lines consist of kinesin proteins which carry cargo, like organelles or vesicles, and literally walk along microtubules. However, as far as man-made systems go, 'nothing comparable to a macroscopic assembly line exists at the nanoscale,' according to Viola Vogel of the Department of Materials at the Swiss Federal Institute of Technology (ETH) in Zurich. 'Imagine if you wanted to build a car by fabricating all of its components, putting them in a glass full of water and hoping that they would self-assemble spontaneously into the finished car.'

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The challenge is to tune the interactions in the system so that the cargo remains stuck to the station when not needed, but can be picked up easily by the shuttle. As a test of principle, Vogel and colleagues used gold nanoparticles coated in anti-biotin antibodies as cargo, and compared loading stations made of biotin-tipped DNA with biotin-tipped polyethylene glycol. Biotinylated microtubules, powered by kinesin motors, act as shuttles rather than conveyor belts, as they do in cells.