Monday, April 19, 2010


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Scientists are reporting that particle size affects the toxicity of zinc oxide, a material widely used in sunscreens. Particles smaller than 100 nanometers are slightly more toxic to colon cells than conventional zinc oxide. Solid zinc oxide was more toxic than equivalent amounts of soluble zinc, and direct particle to cell contact was required to cause cell death. Their study is in ACS' Chemical Research in Toxicology, a monthly journal.

Philip Moos and colleagues note that there is ongoing concern about the potential toxicity of nanoparticles of various materials, which may have different physical and chemical properties than larger particles. Barely 1/50,000 the width of a human hair, nanoparticles are used in foods, cosmetics and other consumer products. Some sunscreens contain nanoparticles of zinc oxide. "Unintended exposure to nano-sized zinc oxide from children accidentally eating sunscreen products is a typical public concern, motivating the study of the effects of nanomaterials in the colon," the scientists note.

Their experiments with cell cultures of colon cells compared the effects of zinc oxide nanoparticles to zinc oxide sold as a conventional powder. They found that the nanoparticles were twice as toxic to the cells as the larger particles. Although the nominal particle size was 1,000 times larger, the conventional zinc oxide contained a wide range of particle sizes and included material small enough to be considered as nanoparticles. The concentration of nanoparticles that was toxic to the colon cells was equivalent to eating 2 grams of sunscreen — about 0.1 ounce. This study used isolated cells to study biochemical effects and did not consider the changes to particles during passage through the digestive tract. The scientists say that further research should be done to determine whether zinc nanoparticle toxicity occurs in laboratory animals and people.

(Photo: iStock)

American Chemical Society


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Researchers from North Carolina State University have developed a new way to shape ceramics using a modest electric field, making the process significantly more energy efficient. The process should result in significant cost savings for ceramics manufacturing over traditional manufacturing methods.

Ceramics make up significant components of an array of products, including insulators, spark plugs, fuel cells, body armor, gas turbines, nuclear rods, high temperature ball bearings, high temperature structural materials and heat shields.

At issue are crystalline defects found in crystalline materials, such as ceramics. “One of these defects is called a grain boundary, which is where crystals with atoms aligned in different directions meet in the material,” says Dr. Hans Conrad, emeritus professor of materials science and engineering at NC State and co-author of the study. These boundaries have electrical charges.

“We found that if we apply an electric field to a material, it interacts with the charges at the grain boundaries and makes it easier for the crystals to slide against each other along these boundaries. This makes it much easier to deform the material.” In other words, the material becomes superplastic – so a ceramic can be shaped into a desirable form using a small amount of force.

“We’ve found that you can bring the level of force needed to deform the ceramic material down to essentially zero, if a modest field is applied,” Conrad says. “We’re talking between 25 and 200 volts per centimeter, so the electricity from a conventional wall socket would be adequate for some applications.”

These findings mean that manufacturers who make anything out of ceramics will be able to do so using less energy. “It will make manufacturing processes more cost-effective and decrease related pollution,” Conrad says. “And these findings also hold promise for use in the development of new ceramic body armor.” Conrad is planning to do additional work using this approach to fabricate ceramic body armor with better properties at a lower cost.

North Carolina State University


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Deep under the Mediterranean Sea small animals have been discovered that live their entire lives without oxygen and surrounded by 'poisonous' sulphides. Researchers writing in the open access journal BMC Biology report the existence of multicellular organisms (new members of the group Loricifera), showing that they are alive, metabolically active, and apparently reproducing in spite of a complete absence of oxygen.

Roberto Danovaro, from the Polytechnic University of Marche, Ancona, Italy, worked with a team of researchers to retrieve sediment samples from a deep hypersaline anoxic basin (DHABs) of the Mediterranean Sea and studied them for signs of life. "These extreme environments", said Danovaro, "have been thought to be exclusively inhabited by viruses, Bacteria and Archaea. The bodies of multicellular animals have previously been discovered, but were thought to have sunk there from upper, oxygenated, waters. Our results indicate that the animals we recovered were alive. Some, in fact, also contained eggs". Electronmicroscopy shows that instead of aerobic mitochondria, these animals possess organelles resembling the hydrogenosomes found previously in unicellular organisms (protozoans) that inhabit anaerobic environments.

The implications of this finding may reach far beyond the darker parts of the Mediterranean Sea floor, according to Lisa Levin of the Scripps Institution of Oceanography. In one of two commentaries accompanying this piece of research, she said, "The finding by Danovaro et al. offers the tantalizing promise of metazoan life in other anoxic settings, for example in the subsurface ocean beneath hydrothermal vents or subduction zones or in other anoxic basins". In the second commentary Marek Mentel and William Martin, from Comenius and Dusseldorf Universities look at the incidence of anaerobic mitochondria and hydrogenosomes in other organisms and focus on the evolutionary significance of the new findings. "The discovery of metazoan life in a permanently anoxic and sulfidic environment provides a glimpse of what a good part of Earth's past ecology might have been like in 'Canfield oceans', before the rise of deep marine oxygen levels and the appearance of the first large animals in the fossil record roughly 550-600 million years ago".

BioMed Central




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