All about Chemistry

Salt nanowire surprise

2010-05-15T19:37:00.000+07:00

Common table salt - normally a brittle crystalline material - can be pulled into nanowires that will extend by more than twice their own length without breaking, US researchers have found.

Nathan Moore and his team at Sandia National Laboratories in Albuquerque, New Mexico, were investigating water adsorption onto salt crystals using an interfacial force microscope (IFM) to probe the salt surface when they stumbled upon their discovery.

'When we poked the salt surface, we saw some unusual force behaviour [between the tip of the microscope probe and the surface]. It seemed crazy at the time, but we thought: "could we be making nanowires?" - of course, seeing is believing, so we put salt in the [transmission electron microscope] and there we saw the nanowires!' (see video at bottom of page)

Time-lapsed transmission electron microscope images showing superelongation of a nanowire

Surprisingly, the salt not only becomes ductile (i.e. able to be pulled into wires), but the wires are also superplastic - they can be extended by more than their own length before breaking. This unusual property is more normally associated with metals and certain ceramics, rather than ionic crystals like salt. The wires can also be compressed back into the crystal, but do tend to bend and buckle.

Part of the cause of this unusual superplasticity could be down to the microscope itself - the beam of electrons from the probe tip, which is used to form the image, can break up the surface of large salt crystals into tiny grains. This allows rapid diffusion of atoms along the grain boundaries, allowing the wires to deform rather than break.

Bombarding salt with the microscope electron beam can also displace chloride ions from the crystal lattice and cause electrons to recombine with sodium ions to form metallic sodium. 'Elemental analysis of the nanowires shows that the composition is predominantly sodium chloride,' says Moore, but there is a reduction in the proportion of chloride. This means that metallic sodium - which has less directional bonding and can also conduct, so could help dissipate charge from the electron beam - could be further improving the superplastic properties of the nanowires.

To see how much of an effect the electron beam has on the growth of the wires, the team tried pulling one out with the beam turned off, turning it back on to get a quick image every so often. They still saw massive elongation of the nanowire, although nowhere near as much as with the beam on, and the wire did eventually break. 'It's very clear the electron beam enhances the superplasticity,' comments Moore, 'but we don't know yet whether or not the electron beam is required to start the wire off.'

'Plasticity [of salt] on this scale is very interesting and also quite surprising,' says Florian Banhart, from the Institute for Physics and Chemistry of Materials (IPCMS) in Strasbourg, France. 'Atomic diffusion is quite a likely explanation for this behaviour as there will be a strong charging effect under the beam, which could create defects in the structure, so diffusion would be enhanced. What is quite convincing is that they see a difference between the situation with and without the electron beam.'

Moore thinks that the possibility of forming nanowires on salt surfaces could have implications in understanding the properties of geological salt deposits and sea salt aerosols, and perhaps help improve understanding about the role salt plays in cloud nucleation and smog formation. 'The fundamental aspects of this are very interesting - you have to wonder if, for example, sea salt particles in the atmosphere are doing the same thing when they collide - are they forming nanowires?'

Phillip Broadwith

Chips and alcohol - a powerful combination

2010-04-15T19:36:00.000+07:00

An on-chip fuel cell that can be powered by a variety of fuels has been developed by Japanese scientists. The fuel can be chosen to suit the cell's application, from laptops to mobile phones, they say.

A variety of fuels can power the microchannel-based on-chip fuel cell

Many research groups are working on miniaturising conventional fuel cells but, as yet, they are not compatible with other micro-devices. Tetsuya Osaka and colleagues from Waseda University, Tokyo, have made a microchannel-based fuel cell that is pump-free, membraneless and air-breathing (it uses oxygen from the air as its oxidant). Its simple monolithic design - its two electrodes are made in a single substrate - means it is easier to make than conventional fuel cells, says Osaka.

"A new approach to develop efficient micro power sources by using micro-electro-mechanical systems"
- Changming Li, Nanyang Technological University, Singapore

Osaka had previously tested the fuel cell using methanol. Methanol is suitable for long-life applications but is toxic, he explains, so he repeated the test using ethanol and 2-propanol. Ethanol is less toxic and renewable, he says, while 2-propanol is suitable for high power devices because it doesn't generate catalyst-poisoning carbon monoxide. He found that ethanol and 2-propanol generated voltages comparable to that of methanol. He also improved the fuel cell's safety by replacing the acidic electrolyte with a phosphate buffer, which kept the pH neutral without significantly affecting the power output.

Changming Li, a fuel cell expert at Nanyang Technological University, Singapore, describes the work as 'a new approach to develop efficient micro power sources by using micro-electro-mechanical systems' and adds that it demonstrates advances in both microfabrication and energy systems.

Osaka says he is working towards integrating the fuel cell with other micro-devices to demonstrate they work in a real system. 'This work will help contribute to the development of micro-devices because they will have their own power source on the same chip,' he predicts. He adds that a possible goal would be an on-chip blood-screening sensor powered by glucose in the blood.

Emma Shiells

Nanotube transistors swing both ways

2010-03-15T19:32:00.000+07:00

Researchers from China and the US have combined titanium dioxide nanoparticles with carbon nanotubes to make light-sensitive transistors that can be made either to switch on or off in response to UV light. The work could be the basis for new types of sensors and optoelectronic devices, the scientists say.

Xuefeng Guo from Peking University, Beijing, teamed up with Dongsheng Xu, also at Peking University, and Colin Nuckolls of Columbia University, New York, combining the Xu group's expertise in making high-quality titanium dioxide nanoparticles with his own group's knowledge of carbon nanotube devices.

The transistors are made by mounting long single walled carbon nanotubes (SWNTs) between chromium and gold electrodes on a silicon wafer backing. They are then dipped in a solution containing the TiO₂ nanoparticles, which have oleic acid groups on their surfaces to anchor them to the nanotubes.

The nanoparticle-coated nanotubes are light-responsive

When UV light shines on the nanoparticles, says Guo, free electrons gather on their surfaces, and can interfere with the current flow in the nanotubes. The team used a particular type of nanotubes which are ambipolar - they can conduct either electrons or positively charged 'holes' where electrons have been removed from the structure. Therefore, depending on which conduction mode is operating in the nanotube at the time, extra electrons will either enhance or block the current - giving the devices their ability to switch either way in response to UV light.

The combination of SWNTs and the TiO₂ nanoparticles - both highly stable materials - allowed the group to make transistors that could be switched many times without degrading. 'For practical applications, reversibility is very important,' explains Guo. 'Up to now, the reversibility of this kind of switch hasn't been very good - after a few cycles the [light sensitive molecules] degraded. We wanted to use more stable stimulus-responsive components to improve the reversibility, which is why we chose inorganic titanium dioxide nanoparticles,' he adds.

'The fact that [the devices] can switch both ways is a very valuable observation,' comments Andrei Khlobystov, a specialist in carbon nanotube technologies from the University of Nottingham, UK.

'Nanotubes and nanoparticles are remarkable materials with interesting properties,' adds Khlobystov, 'so by making composite materials combining the two you have a good chance of retaining their intrinsic functional properties, but you can also come up with new properties. But the mechanisms of interactions between nanoparticles and nanotubes are not very well understood, and that's something this work is trying to address.' He adds that Guo's explanation of the switching effects sounds viable, but might be a little simplistic, given the intricacies of nanotube and nanoparticle behaviour - 'I wouldn't be surprised if there was something much more complex going on!'

Guo agrees that the interplay between the nanoparticles and nanotubes is crucial. 'The fact that carbon nanotubes can facilitate photoinduced charge separation in the nanoparticles implies that these hybrid materials might be good candidates for switching, sensing and photocatalysis applications,' he explains. He adds that elements that switch in opposite ways might also be combined into arrays or combined with functional molecular materials to make logic gates and related devices.

Phillip Broadwith

A good egg

2010-02-15T19:29:00.000+07:00

UK and Dutch scientists have mimicked an ancient Chinese culinary technique of preserving eggs to study how proteins cause disease.

Erika Eiser from the University of Cambridge and colleagues looked at how proteins in egg whites altered during this preservation process. The Chinese method involves wrapping raw eggs in an alkaline paste of lime, clay, salt, ash and tea and storing these so-called century eggs for several months. Eiser modified the method by incubating a boiled egg in a strong alkaline sodium hydroxide-salt solution for up to 26 days.

Hard boiled egg whites become a transparent gel in an alkaline solution

After peeling back the shell, Eiser found that the egg white had transformed into a gel. This transformation is caused by changes in the way protein strands, called ovalbumin, in the white are held together. Boiling an egg causes bonds between the protein strands to break and the proteins to partially unfold. The proteins then come together, or aggregate, in a different way to form the opaque and brittle white. The transformation was thought to be irreversible, but the alkali causes the proteins in the white to aggregate into fine strands to form a transparent and elastic gel. Eiser found that the gel was more stable than the white, and could be heated without changing its structure.

Paul Bartlett, an expert in colloids and protein aggregation at the University of Bristol, UK, comments that Eiser's findings 'will be important for understanding protein gels and will inspire more work in colloidal materials.'

'Similar chemical transformations could be used to change the properties of protein aggregates not only in food but also in other biomaterials,' says Eiser, who plans to test the method on different proteins. 'If we understand the mechanism that drives aggregation then we could slow it down or reverse the aggregation into something else.' This could be important in preventing diseases caused by unnatural protein aggregation such as Alzheimer's.

Anna Roffey

Catalyst kinetics revealed

2010-01-15T19:26:00.000+07:00

French and UK scientists have developed a spectroscopy technique that has elucidated the reaction mechanism of a silver-alumina catalyst. The researchers say their approach should allow scientists to fine tune both this catalyst and other industrial heterogeneous catalysts to improve performance.

Silver-alumina catalysts are used in lean burn engines, which conserve fossil fuels and limit carbon dioxide emissions but produce nitrogen oxide, a greenhouse gas. Silver-alumina catalysts help remove this nitrogen oxide by reacting it with carbon monoxide. However, the lack of suitable experimental methods to help clarify exactly how supported precious metal catalysts like this work at the molecular level has proved a major obstacle in improving efficiency.

Now, Frédéric Thibault-Starzyk from ENSICAEN, the Université de Caen, France, and colleagues, have combined a high-time resolution Fourier-transform infrared spectrometer (FTIS) with a femtosecond laser and revealed a key intermediate step in the reaction between carbon monoxide and nitric oxide. Using their technique they observed a 2 microsecond flip of a cyanide group from a silver nanoparticle to the alumina support, revealing the importance of the silver-alumina interface.

Thibault-Starzyk and Heike Arnolds, now at the University of Liverpool, UK, triggered the reaction of the silver-alumina catalyst using a femtolaser at David A King's lab at the University of Cambridge, UK. 'Our idea for using a femtosecond laser was that we would avoid the actual heating of the whole surface and thus prevent thermal desorption of the molecules,' explains Thibault-Starzyk.

The team then tracked the reaction using a FTIS, the time resolution capabilities of which meant they could completely change the timescale at which they were looking at the chemistry. 'People using FTIS tend to look at around ten spectra a second,' says Thibault-Starzyk. 'So going to the nanosecond was a complete change of approach and allowed us to see molecular movement on the surface of the catalyst.'

The new intermediate the team detected between the silver cluster and the alumina support may lead to more efficient silver-alumina catalysts for use in lean burn engines, or in any metal-supported catalysis, suggests Thibault-Starzyk.

Luca Lietti, a catalysis expert at the Polytechnico de Milano, Italy, agrees. He thinks the technique could be applied to many processes and 'could be very interesting for people working in the field of catalysis and the detection of intermediates in general.' By knowing how a reaction proceeds and knowing the intermediates participating in the reaction, Lietti suggests that more active and more selective catalysts could be developed.

James Urquhart

'Printing' organs with hydrogels

2009-12-15T19:22:00.000+07:00

Dutch researchers have developed a way to 'print' stable cell-containing scaffolds, creating a method that could one day be used to help make tailor-made tissue grafts and even grow whole synthetic organs.

Jacqueline Alblas and her group from the University Medical Centre in Utrecht, The Netherlands, have made polymer hydrogel 'ink' materials that are fluid enough to be used in a printing device, but can later be converted into stable structures that don't fall apart when handled. They can incorporate stem cells into the hydrogels to begin the process of tissue generation within the scaffolds.

The cell-laden hydrogel is printed as a long strand, which can be built up into multi-layered structures, explains Alblas. 'We made a layer of strands, then a cross-hatched layer on top of that to build upwards, but you can also print circles to make tubes.' By combining different structures impregnated with different types of cells, it should be possible to build much more complex structures such as tissue grafts that have blood vessels built into them, she adds.

Scaffold structures are built up from layers of cross-hatched hydrogel strands

Two problems in printing tissues and organs are the formation of defined, versatile shapes and keeping the cells alive throughout the process and beyond. Hydrogel polymers are particularly suitable in this last respect as they provide the highly hydrated environment required by cells and allow nutrients and oxygen to diffuse within the structures.

However, Alblas explains, while many hydrogels can hold their shape after printing, they are often very soft and easily squashed when handled, which can ruin detailed structures. To tackle this problem, the team modified an existing hydrogel to make it photopolymerisable. Shining UV light on the printed structures activates a crosslinking reaction that fixes the shape of the gel - 'photopolymerisation means that you can handle the structure, it's not a snotty substance anymore, you can just pick it up!' says Alblas.

The team are initially concentrating on structures for bone grafts, so they incorporated cells from goat bone marrow into their hydrogel. It is important that the cells can survive and grow within the structure, and they found that the cells survived much better in the new photopolymerisable gel than in non-crosslinked versions, lasting for up to three weeks rather than a few days. 'The modification of the gel makes it much more suitable for loading with cells,' says Alblas. 'We think this might be because the crosslinking prevents any leftover monomers from disrupting the plasma membranes of the cells.'

Glenn Prestwich from the University of Utah in Salt Lake City, US, who is also researching hydrogel materials for organ printing, thinks that this is a clever combination of approaches: 'It addresses the key physicochemical problems of being soft for printing but robust for handling, making it a potentially useful research tool.'

However, Prestwich sees some problems with the group's choice of materials: 'The major challenges in organ printing are in the maturation, implantation, and integration stages,' he explains, 'and these synthetic polymers are only slowly biodegradable, so don't really address the critical design criteria for a clinically useful material.' Alblas agrees that these polymers might not be ideal for clinical applications, saying 'they're not very natural gels, and we don't have a lot of data on the in vivo characteristics, but our main focus was on the printing properties.'

Phillip Broadwith

Chemical pollution gets personal

2009-11-15T19:20:00.000+07:00

Scientists have often experimented on themselves to prove a point. Now two Canadian environmentalists have detailed the rise and fall of chemicals in their own bodily fluids after using everyday products. And they were shocked by the results.

Bruce Lourie is president and chair and Rick Smith is executive director of Canadian environmental organisation Environmental Defence. In their book Slow death by rubber duck, the pair detail a weekend testing spree incorporating regular blood and urine sampling. Indoors for 12-hour shifts, they used typical amounts of personal care products and a plug-in air freshener, in a room with stain-repellent furnishings and carpets. 'We set only one ironclad rule: our efforts had to mimic real life,' says Smith.

Of six different phthalates in the testing regime, rocketing levels of monoethyl phthalate (MEP) - which the body metabolises from diethyl phthalate (DEP) the most common phthalate in cosmetics and personal care products - were most stark. Levels in urine went from 64 to 1410ng/ml. According to the European Commission's Scientific Committee for Cosmetic Products (SCCP), traces of up to 100 ppm total or per substance pose no risk to health, although traces of banned phthalates are sometimes present due to other possible uses, such as in packaging. Phthalates are plasticising chemicals, linked to abnormal reproductive development.

Eating just three meals containing tuna more than doubled Lourie's blood mercury levels to 7.55µg/L in less than 48 hours. The US Environmental Protection Agency reference dose level for the neurotoxin is 5.8µg/L, which if exceeded is cause for concern. Levels of bisphenol A - an endocrine disruptor linked to breast and prostate cancer - increased 7.5 times after eating canned foods from a microwavable, polycarbonate plastic container.

Eating three tuna meals made Lourie's blood mercury levels soar

Triclosan (an antibacterial found in toothpaste, soap and deodorant) levels in Smith's urine jumped from 2.47ng/ml to 7180ng/ml after exposure - increasing 2900 times. Smith usually avoids antibacterial products, so his baseline level was low compared to the average North American (mean 13ng/mL). Triclosan bioaccumulates and has been found in infant cord blood and breast milk. Studies suggest it is an endocrine disruptor and affects thyroid function, and there is ongoing debate about its role in bacterial resistance. The SCCP states that Triclosan is safe.

Smith avoided everyday products containing Triclosan, phthalates and bisphenol A for 48 hours before the experiment, and Lourie ate no fish for a month. Testing protocols were suggested by Harvard School of Public Health phthalate expert, Susan Duty.

High levels of chemicals in urine mean the body is doing a good job of excreting them, rather than telling us what remains in the body. But that is not really the issue, Smith told Chemistry World: 'All the chemicals we tested have been linked to serious human health problems. All have easy replacements. Any proper regulatory system would aim to eliminate them from the human body completely.'

The experiment is unusual in that it 'represents a snapshot of the exposure they are getting from these products,' according to Professor Stelvio Bandiera, an expert on environmental chemicals and health at the University of British Columbia faculty of Pharmaceutical Sciences. Typical studies look for population trends, and assume chemical levels in test subjects are at equilibrium. The authors' experiment showed that the products contained chemicals and that these entered their bodies - previous experiments have not considered how quickly the levels rise.

Bandiera suggests that the snapshot approach is useful for raising awareness: 'Certain products do contain these chemicals. The public is poorly informed about the kinds of chemicals they are exposed to on a regular basis in food and consumer products.'

The levels in these products are safe according to Canadian and US authorities, and Bandiera says that there's no immediate health concern. However, for babies and young children he adds a caution: 'We don't want them to be exposed unduly to chemicals that they are unable to metabolise, and will stay with them for a long time.'

The authors accept that their results are illustrative, but demonstrate that careful choices dramatically affect levels of 'personal pollution'. Bandiera agrees that 'you can make a conscious choice - you may not be able to avoid [specific chemicals] completely but you can reduce your exposure.'

'Testing of individuals for measurable amounts of pollution has become commonplace, though our demonstration of increases and decreases in pollution levels is brand new,' Smith says.

Helen Carmichael

Exposing explosive fingerprints

2009-10-15T19:15:00.000+07:00

US scientists have used infrared (IR) spectroscopy to distinguish between overlapping fingerprints and reveal their chemical history.

Ira Levin and colleagues, at the National Institutes of Health, Bethesda, claim the technique can identify latent (invisible) fingerprints containing contaminants, such as drugs or explosives, and filter out overlapping fingerprints originating from the natural secretions found in fingertips. Previous IR studies of fingerprints have been based only on natural secretions, says Levin, and so failed to provide this extra forensic evidence.

"Not only can IR spectroscopic imaging identify controlled substances, such as explosives, but it can also link these chemicals with the person who touched them"
- Claude Roux, University of Technology, Sydney, Australia

The group took an IR spectroscopic image of two overlapping fingerprints - one natural fingerprint and one containing an explosive. They then distinguished the contaminated fingerprint's spectral image from the overlapping print using a mathematical method called multivariate analysis. The resulting image clearly showed the explosive in between the ridges of the fingerprint. 'You can obtain a fingerprint with the associated forensic evidence which can go through MI5 or FBI databases to target an individual,' explains Levin.

Claude Roux, director of the Centre for Forensic Science at the University of Technology, Sydney, Australia, comments that although this is not the first research to be done in this area, it is 'interesting and very relevant because it combines two major aspects of forensic investigations: human identification and chemical characterisation. It shows that not only can IR spectroscopic imaging identify controlled substances, such as explosives, but it can also link these chemicals with the person who touched them.'

Levin says works needs to be done to make the technique more easily accessible but he is confident that it will be useful to forensic teams worldwide.

Jane Hordern

Wine's chemical memory

2009-09-15T19:08:00.000+07:00

European researchers have discovered that even 10 years after bottling, wine still holds the chemical signature of the forest from which the barrel used to age it was made. The approach could be used to detect wine fraud in the future, say the team.

The chemical composition of wine depends on a complex mixture of factors including how and where the grapes are grown, how the wine is made and the aging process used. The volatile and polyphenolic compounds involved in the taste, smell and therapeutic effects of wine have been well studied - but have generally only been considered one chemical at a time.

Due to wine's complexity, an approach that looks at many compounds at once could provide new insights into its chemical composition. A European team, led by Régis Gougeon, University of Bourgogne, Dijon, France, and Philippe Schmitt-Kopplin, Helmholtz centre in Munich, Germany, are the first to take such a holistic approach, studying wine metabolomics.

'By using the most recent advances in ultra high resolution mass spectrometry, we have shown that it is now possible to provide an instantaneous picture of how diverse the chemical composition of a wine can be,' Gougeon and Schmitt-Kopplin told Chemistry World.

The researchers used a high-field ion cyclotron resonance-Fourier transform mass spectrometer to collect their data, one of only 10 of its size worldwide. The machine generates a phenomenally large amount of data for each type of wine analysed; for example, the 1995 Vosne Romanée - a red burgundy - generated 17 400 peaks in the resulting spectrum. After statistical processing the team were able to attribute these peaks to 1180 unique elemental CHONS compositions.

High resolution mass spectrometry can reveal the history of a bottle of wine

To demonstrate the potential of the approach, the team concentrated their research on wine known to have been aged in oak barrels from nine different forests across France. They showed that they could match the chemical fingerprints of the oak with the chemical composition of the wine, and therefore identify in which of the nine forests the oak for the barrels used to age the wine was grown.

The metabolomic approach was crucial to making this link, say the team. The chemical composition of individual trees in a single forest varies considerably, and only some of the trees' chemical signature is actually transferred to the wine. Add to this the fact that some of the compounds will undergo chemical reactions while the wine is in the bottle, and the result is a hugely complex chemical combination. 'At that point, only holistic and ultra high resolution approaches can possibly relate the instantaneous chemical signature to original information,' explain Gougeon and Schmitt-Kopplin. No other approach - analytical or sensory - has been able to significantly discriminate wines according to the species or the origin of the oak used for the barrels before, they say.

The scientists showed that the approach works on initial grape extracts right through to wines that had been aged in the bottle for 10 years, in red and white wine, and in champagne.

'The holistic approach allows us to consider it as a complex biological system in constant evolution, and to pick at a particular moment how each instrument of the orchestra contributes to the concert,' say Gougeon and Schmitt-Kopplin.

The approach should also work on different types of wood, grown all over the world and even different types of beverage aged in wooden barrels, say the researchers - whisky is next on their list.

The price of the mass spectrometer means that the use of the technique is currently limited to fundamental research, but if the concept could be transferred to lower resolution - and therefore cheaper - machines in the future, it could become a tool for detecting wine fraud, say Gougeon and Schmitt-Kopplin.

Susan Ebeler from the University of California Davis, US, an expert in using analytical techniques to study the chemistry of wine, describes this work as 'an exciting use of some very nice technology'.

'It could be used eventually in the authentication of wine; by region, variety and processing,' she adds.

Nina Notman

Water Chemistry

2009-08-28T18:51:00.000+07:00

Both the harmful effects of radiation upon biological systems (induction of cancer and acute radiation injuries) and the useful effects of radiotherapy involve the radiation chemistry of water. The vast majority of biological molecules are present in an aqueous medium; when water is exposed to radiation, the water absorbs energy, and as a result forms chemically reactive species that can interact with dissolved substances (solutes). Water is ionized to form a solvated electron and H₂O⁺, the H₂O⁺ cation can react with water to form a hydrated proton (H₃O⁺) and a hydroxyl radical (HO^.). Furthermore, the solvated electron can recombine with the H₂O⁺ cation to form an excited state of the water, this excited state then decomposes to species such as hydroxyl radicals (HO^.), hydrogen atoms (H^.) and oxygen atoms (O^.). Finally, the solvated electron can react with solutes such as solvated protons or oxygen molecules to form respectively hydrogen atoms and dioxygen radical anions. The fact that oxygen changes the radiation chemistry might be one reason why oxygenated tissues are more sensitive to irradiation than the deoxygenated tissue at the centre of a tumor. The free radicals, such as the hydroxyl radical, chemically modify biomolecules such as DNA, leading to damage such as breaks in the DNA strands. Some substances can protect again radiation-induced damage by reacting with the reactive species generated by the irradiation of the water.

It is important to note that the reactive species generated by the radiation can take part in following reactions, this is similar to the idea of the non-electrochemical reactions which follow the electrochemical event which is observed in cyclic voltammetry when a non-reversible event occurs. For example the SF₅ radical formed by the reaction of solvated electrons and SF₆ undergo further reactions which lead to the formation of hydrogen fluoride and sulfuric acid.^[18]

In water the dimerisation reaction of hydroxyl radicals can form hydrogen peroxide, in saline systems the reaction of the hydroxyl radicals with chloride anions form hypochlorite anions.

It has been suggested that the action of radiation upon underground water is responsible for the formation of hydrogen which was converted by bacteria into methane.[2].^[19] A series of papers on the subject of bacteria living under the surface of the earth which are fed by the hydrogen generated by the radiolysis of water can be read on line.^[20]

Source: Wikipedia

Greenhouse Effect

2009-07-28T18:48:00.000+07:00

The term "greenhouse effect" can be a source of confusion as actual greenhouses do not function by the same mechanism the atmosphere does. Various materials at times imply incorrectly that they do, or do not make the distinction between the processes of radiation and convection^[26].

The term 'greenhouse effect' originally came from the greenhouses used for gardening, but as mentioned the mechanism for greenhouses operates differently.^[27] Many sources make the "heat trapping" analogy of how a greenhouse limits convection to how the atmosphere performs a similar function through the different mechanism of infrared absorbing gases.^[28]

A greenhouse is usually built of glass, plastic, or a plastic-type material. It heats up mainly because the sun warms the ground inside it, which then warms the air in the greenhouse. The air continues to heat because it is confined within the greenhouse, unlike the environment outside the greenhouse where warm air near the surface rises and mixes with cooler air aloft. This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature will drop considerably. It has also been demonstrated experimentally (Wood, 1909) that a "greenhouse" with a cover of rock salt heats up an enclosure similarly to one with a glass cover.^[29] Greenhouses thus work primarily by preventing convection; the atmospheric greenhouse effect however reduces radiation loss, not convection.^[30]^[27]

Pollution Effect

2009-06-28T18:43:00.000+07:00

Human health

Overview of main health effects on humans from some common types of pollution. ^[15] ^[16] ^[17]

Adverse air quality can kill many organisms including humans. Ozone pollution can cause respiratory disease, cardiovascular disease, throat inflammation, chest pain, and congestion. Water pollution causes approximately 14,000 deaths per day, mostly due to contamination of drinking water by untreated sewage in developing countries. Oil spills can cause skin irritations and rashes. Noise pollution induces hearing loss, high blood pressure, stress, and sleep disturbance. Mercury has been linked to developmental deficits in children and neurologic symptoms. Lead and other heavy metals have been shown to cause neurological problems. Chemical and radioactive substances can cause cancer and as well as birth defects.

Ecosystems

Sulphur dioxide and nitrogen oxides can cause acid rain which lowers the pH value of soil.
Nitrogen oxides are removed from the air by rain and fertilise land which can change the species composition of ecosystems.
Soil can become infertile and unsuitable for plants. This will affect other organisms in the food web.
Smog and haze can reduce the amount of sunlight received by plants to carry out photosynthesis and leads to the production of tropospheric ozone which damages plants.
Invasive species can out compete native species and reduce biodiversity. Invasive plants can contribute debris and biomolecules (allelopathy) that can alter soil and chemical compositions of an environment, often reducing native species competitiveness.
Biomagnification describes situations where toxins (such as heavy metals) may pass through trophic levels, becoming exponentially more concentrated in the process.
Carbon dioxide emissions cause ocean acidification, the ongoing decrease in the pH of the Earth's oceans as CO₂ becomes dissolved.
The emission of greenhouse gases leads to global warming which affects ecosystems in many ways.

Source: Wikipedia

HAZARDOUS CHEMICAL SPILLS & EMERGENCY RESPONSE PROCEDURES

2009-04-28T17:44:00.000+07:00

A. Definition of Chemical Spills - Emergency & Non-emergency

The range and quantity of hazardous substances used in laboratories require preplanning to respond safely to chemical spills. The cleanup of chemical spills should only be accomplished by knowledgeable and experienced people. Spill kits with instructions, absorbents, reactants, and protective equipment should be available to clean up minor spills.

Three factors determine if a hazardous materials spill is a non-emergency or an emergency.

1. How much was spilled - if the amount of the material spilled is more than one liter, it is considered a major spill and you should contact the Chemical Safety Office for assistance.

2. What are the hazards of the material spilled - if the spill is less than one liter, but presents an immediate danger to health, safety, the environment, or is an immediate fire hazard, it is considered a major spill and you should follow Emergency Response Procedures for Chemical Spills.

3. Where is the Spill - if the spill is outside of the laboratory or outside of the area where the material is normally used, and/or there is no trained person available to clean up the spill, you should contact the Chemical Safety Office for assistance.

Note: All laboratory workers, or persons using hazardous materials must be trained in how to clean up the materials they are using. Spill Kits are required in all areas where chemicals are used or stored - employees who work in those areas must be trained in how to use the kits and in how to activate the Emergency Response Procedures for Major Spills.

B. Non-Emergency - Minor Chemical Spill

Small spills (<>

a. Alert people in immediate area of spill.
b. Wear protective equipment - including safety goggles, gloves, long-sleeve lab coat.
c. Avoid breathing vapors from the spill.
d. Confine spill to small area.
e. Use appropriate kit to neutralize and absorb inorganic acids and bases. Collect residue, place in container , fill out blue waste tag, and contact the Chemical Safety Office at ext. 1-2663 for disposal..
f. For other chemicals, use appropriate kit or absorb spill with vermiculite, dry sand, or diatomaceous earth. Collect residue, place in container and dispose as chemical waste.
g. Clean spill area with water.

C. Spill Kits:

Chemical Spill Kits shall be available in the laboratory. These materials shall include:

a. Neutralizing agents such as sodium carbonate or sodium bisulfate
b. Absorbents such as vermiculite. Paper towels, rags, and sponges may be used, but caution should be exercised because some chemicals may react upon contact with them.

Commercial spill kits are available that have instructions, absorbents,

D. Emergency Response Procedures - Major Spill

Large Spills (> 1 Liter or a material presents an immediate fire, safety, environmental, or health hazard regardless of quantity). Examples: Spill of greater than 1 Liter of ethanol, methanol, strong acids or bases or any quantity of highly volatile organics, and mercury compounds

Chemical Weapon

2009-03-27T08:17:00.000+07:00

Chemical warfare is warfare (and associated military operations) using the toxic properties of chemical substances to kill, injure or incapacitate an enemy.

Chemical warfare is different from the use of conventional weapons or nuclear weapons because the destructive effects of chemical weapons are not primarily due to any explosive force. The offensive use of living organisms (such as anthrax) is considered to be biological warfare rather than chemical warfare; the use of nonliving toxic products produced by living organisms (e.g., toxins such as botulinum toxin, ricin, or saxitoxin) is considered chemical warfare under the provisions of the Chemical Weapons Convention. Under this Convention, any toxic chemical, regardless of its origin, is considered as a chemical weapon unless it is used for purposes that are not prohibited (an important legal definition, known as the General Purpose Criterion).

About 70 different chemicals have been used or stockpiled as Chemical Weapons (CW) agents during the 20th century. Chemical weapons are classified as weapons of mass destruction by the United Nations, and their production and stockpiling was outlawed by the Chemical Weapons Convention of 1993. Under the Convention, chemicals that are toxic enough to be used as chemical weapons, or may be used to manufacture such chemicals, are divided into three groups according to their purpose and treatment:

Schedule 1 – Have few, if any, legitimate uses. These may only be produced or used for research, medical, pharmaceutical or protective purposes (i.e. testing of chemical weapons sensors and protective clothing). Examples include nerve agents, ricin, lewisite and mustard gas. Any production over 100 g must be notified to the OPCW and a country can have a stockpile of no more than one tonne of these chemicals.
Schedule 2 – Have no large-scale industrial uses, but may have legitimate small-scale uses. Examples include dimethyl methylphosphonate, a to sarin but which is also used as a flame retardant and Thiodiglycol which is a precursor chemical used in the manufacture of mustard gas but is also widely used as a solvent in inks.
Schedule 3 – Have legitimate large-scale industrial uses. Examples include phosgene and chloropicrin. Both have been used as chemical weapons but phosgene is an important precursor in the manufacture of plastics and chloropicrin is used as a fumigant. Any plant producing more than 30 tonnes per year must be notified to, and can be inspected by, the OPCW.

Source from http://encyclopedia.thefreedictionary.com/chemical+weapon

Chinese Tea Kills Malaria

2009-03-16T03:51:00.000+07:00

Malaria kills about two million people a year worldwide. The disease is spread by a parasite carried in mosquitoes. Two drugs have been used to treat most malaria. They are quirine and chloroquine. However, the drugs are no longer effective against malaria in many parts of the world.

Recently a scientific study showed why a kind of Chinese tea may be the most effective drug against the disease malaria. They study showed that a chemical in the tea destroys the malaria parasite.

The tea is called quinhaosu. Chinese doctors have been using the tea to treat fever. It contains an active chemical artemisin. In malaria patients, artemisin starts a reaction that poisons the malaria parasite. The parasite is unable to destroy the iron in hemoglobin. The tea’s active chemical artemisinin sticks to the iron. The resulting chemical reaction releases molecules called free radicals. These molecules destroy major parts of the malaria parasite.

Source from http://luponfirehouse.blogspot.com/search/label/Health

DRUGS and Their Side Effects - What to Watch For

2009-03-02T07:45:00.000+07:00

Each year, every physician who prescribes medicines receives a new edition of the Physicians' Desk Reference (PDR). Supplements are sent out whenever new drugs are introduced or we learn new things about old ones. This book serves as a sort of pharmaceutical bible for most doctors. It tells them what drugs will benefit which patients; what side effects to watch for; what specific contraindications there may be to the drug. (For example, certain antibiotics should not be given to patients whose kidney function is impaired, since the drug is excreted by the kidney.) In brief, the PDR contains all the information the physician ought to have about most of the medicines he prescribes.

Blood pressure medications are notorious for causing a decline in both libido and potency. However, the mere suggestion that a drug might cause impotency is often enough to guarantee its occurrence in the patient.

Many drugs, particularly some of the anticancer drugs, have side effects that are not only annoying but potentially dangerous. For example, many of the anticancer drugs can cause a patient's hair to fall out; some cause nausea; others can cause dangerous decrease in the production of bone marrow. The patients for whom these drugs are prescribed should be, and almost invariably are , told about these side effects. The drugs must be used, despite their side effects, because they are essential to the proper treatment of cancer. Fortunately, some of the side effects - such as hair loss - are temporary; and the bone marrow is watched carefully so the drug dosage can be decreased or even discontinued, if necessary, to allow the marrow to regain its normal productivity.

Some drugs have side effects that are invariable but innocuous. They are frightening only when the doctor has forgotten to warn the patient about them. For example, one of the drugs used frequently to treat bladder infections contains an ingredient that turns urine red.

By now most people know enough about drugs to be wary of the doctor who prescribes penicillin, say, without first asking if the patient is allergic to it. A first allergic reaction to penicillin can cause swelling of the face, a severe generalized rash and even shock; a second may be lethal. It is routine now, in most hospitals, for the admitting nurse or aide to ask the patient if he ir she is allergic to anything, and to list those allergies on the patient's chart.

Unfortunately, even though extensive testing is required before pharmaceutical companies are allowed to market new drugs, sometimes serious side effects surface many years later. Recent reports, for example, suggest that the use of femal hormones (estrogen), particularly in large doses may after several years cause an increased incidence of cancer of the inner lining of the uterus. Physicians this have an obligation to weigh the benefits from taking estrogen to be gained by the patient against the added risk to which she will be subjected - and then decided whether it is, of course, morally and legally obligatory for the doctor to want the patient of the added risk and to let her decide. Some patients will decide to take the medicine anyway; others will choose to forego it.

The incidence of adverse reactions to drugs is high - generally estimated to be about 20 percent - and at any given time about 5 percent of the patients at any hospital are there because they are being treated for drug reactions. These figures are indeed alarming, but you should remember that in most instances the drug that cause the adverse reaction also helped the patient and perhaps even saved his or her life. The man who is admitted to the hospital because of digitalis toxicity in all likelihood needs digitalis to help his dosage has been adjusted to a proper level he will probably continue to take digitalis. The diabetic woman admitted to the hospital because of insulin shock deos not stop taking insulin; she needs the insulin to control her diabetes, and the risk of rare attacks of insulin shock is a reasonable price to pay for the many years of life and health the drug gives her.

Nevertheless, there is strong evidence that physicians prescribe and patients consume many more drugs than are necessary. It is admittedly much easier for a doctor to prescribe a tranquilizer than to spend an hour or two trying to help a patient understand and get rid of her anxiety; it's also easier to say yes to the patient who wants "a shot of penicillin" to cure his cold than to sit down and explain the colds are self-limited diseases, caused by viruses that are not sensitive to antibiotics.

The moral of all this is that it is best not to take any medicine unless you are sure its benefits outweigh its risks, and even then to be aware that any unusual symptoms you develop after you've started taking the drug may be caused by that drug. If such symptoms develop, report them immediately to your doctor. He may decrease the dosage, shift you to a different drug or take you off medication entirely.

There is unfortunately, no certain way to predict which patient will develop an adverse reaction to any given drug. The one that is "good" for you may be "bad" for someone else. Drug companies try to make their drugs as safe as possible, and doctors try choose appropriate drugs and proper dosages for each patient, but the system is not and cannot be foolproof. Where medicines are concerned, the patient must always be cautious - as this doctor-patient now know.

(By William A. Nolan, M.D.)

Requirements for Areas Containing a Carcinogen

2009-02-22T07:34:00.000+07:00

A regulated area shall be established by an employer where a carcinogen addressed by this section is manufactured, processed, used, repackaged, released, handled or stored. All such areas shall be controlled in accordance with the requirements for the following category or categories describing the operation involved:
(1) Isolated systems.
Employees working with a carcinogen addressed by this section within an isolated system such as a “glove box” shall wash their hands and arms upon completion of the assigned task and before engaging in other activities not associated with the isolated system.
(2) Closed system operation.
(i) Within regulated areas where the carcinogens addressed by this section are stored in sealed containers, or contained in a closed system, including piping systems, with any sample ports or openings closed while the carcinogens addressed by this section are contained within, access shall be restricted to authorized employees only.
(ii) Employees exposed to 4-Nitrobiphenyl; alpha-Naphthylamine; 3,3’-Dichlorobenzidine (and its salts); beta-Naphthylamine; benzidine; 4-Aminodiphenyl; 2-Acetylaminofluorene; 4-Dimethylaminoazo-benzene; and N-Nitrosodimethylamine shall be required to wash hands, forearms, face, and neck upon each exit from the regulated areas, close to the point of exit, and before engaging in other activities.
(3) Open-vessel system operations.
Open-vessel system operations as defined in paragraph (b)(13) of this section are prohibited.
(4) Transfer from a closed system, charging or discharging point operations, or otherwise opening a closed system.
In operations involving “laboratory-type hoods,” or in locations where the carcinogens addressed by this section are contained in an otherwise “closed system,” but is transferred, charged, or discharged into other normally closed containers, the provisions of this paragraph shall apply.
(i) Access shall be restricted to authorized employees only.
(ii) Each operation shall be provided with continuous local exhaust ventilation so that air movement is always from ordinary work areas to the operation. Exhaust air shall not be discharged to regulated areas, nonregulated areas or the external environment unless decontaminated. Clean makeup air shall be introduced in sufficient volume to maintain the correct operation of the local exhaust system.
(iii) Employees shall be provided with, and required to wear, clean, full body protective clothing (smocks, coveralls, or long-sleeved shirt and pants), shoe covers and gloves prior to entering the regulated area.
(iv) Employees engaged in handling operations involving the carcinogens addressed by this section must be provided with, and required to wear and use a half-face filtertype respirator with filters for dusts, mists, and fumes, or air-purifying canisters or cartridges. A respirator affording higher levels of protection than this respirator may be substituted.
(v) Prior to each exit from a regulated area, employees shall be required to remove and leave protective clothing and equipment at the point of exit and at the last exit of the day, to place used clothing and equipment in impervious containers at the point of exit for purposes of decontamination or disposal. The contents of such impervious containers shall be identified, as required under paragraphs (e)(2), (3), and (4) of this section.
(vi) Drinking fountains are prohibited in the regulated area.
(vii) Employees shall be required to wash hands, forearms, face, and neck on each exit from the regulated area, close to the point of exit, and before engaging in other activities and employees exposed to 4-Nitrobiphenyl; alpha-Naphthylamine; 3,3’- Dichlorobenzidine (and its salts); beta-Naphthylamine; Benzidine; 4-Aminodiphenyl; 2-Acetylaminofluorene; 4-Dimethylaminoazo-benzene; and N-Nitrosodimethylamine shall be required to shower after the last exit of the day.
(5) Maintenance and decontamination activities.
In cleanup of leaks of spills, maintenance, or repair operations on contaminated systems or equipment, or any operations involving work in an area where direct contact with a carcinogen addressed by this section could result, each authorized employee entering that area shall:
(i) Be provided with and required to wear clean, impervious garments, including gloves, boots, and continuous-air supplied hood in accordance with §1910.134;
(ii) Be decontaminated before removing the protective garments and hood;
(iii) Be required to shower upon removing the protective garments and hood.

White phosphorus (weapon)

2009-02-12T17:59:00.000+07:00

White phosphorus (WP) is a flare- and smoke-producing incendiary device or smoke-screening agent that is made from a common allotrope of the chemical element phosphorus. The main utility of white phosphorus munitions is to create smokescreens to mask movement from the enemy, or to mask his fire. In contrast to other smoke-causing munitions, WP burns quickly causing an instant bank of smoke. As a result of this, WP munitions are very common -- particularly as smoke grenades for infantry; loaded in defensive grenade dischargers on tanks and other armored vehicles; or as part of the ammunition allotment for artillery or mortars.

However, white phosphorus has a secondary effect. While much less efficient than ordinary fragmentation effects in causing casualties, white phosphorus burns quite fiercely and can set cloth, fuel, ammunition and other combustibles on fire. It also can function as an anti-personnel weapon with the compound capable of causing serious burns or death. The agent is used in bombs, artillery, and mortars, short-range missiles which burst into burning flakes of phosphorus upon impact. White phosphorus is commonly referred to in military jargon as "WP". The slang term "Willy(ie) Pete" or "Willy(ie) Peter", dating from World War I and common at least through the Vietnam War, is still occasionally heard.

White phosphorus weapons are controversial today because of their potential use against civilians. While the Chemical Weapons Convention does not designate WP as a chemical weapon, various groups consider it to be one. In recent years, the United States, Israel, and Russia have used white phosphorus in combat.

The United States' use of white phosphorus in Iraq in the Iraq War has resulted in considerable controversy amongst critics of the war. Initial field reports referred to white phosphorus use against insurgents, but its use was officially denied until November 2005, when the Department of Defense admitted to the use of white phosphorus while stating that its use for producing obscuring smoke is legal and does not violate the CWC. A DoD spokesman has also admitted that WP "was used as an incendiary weapon against enemy combatants", though not against civilians.

Source from wikipedia

Formaldehyde

2009-01-22T13:00:00.000+07:00

Formaldehyde (IUPAC name methanal) is a chemical compound with the formula H₂CO. It is the simplest aldehyde. Formaldehyde exists in several forms aside from H₂CO: the cyclic trimer trioxane and the polymer paraformaldehyde. It exists in water as the hydrate H₂C(OH)₂. Aqueous solutions of formaldehyde are referred to as formalin. "100%" formalin consists of a saturated solution of formaldehyde (roughly 40% by mass) in water, with a small amount of stabilizer, usually methanol to limit oxidation and polymerization. It is produced on a substantial scale of 6M tons/y. In view of its widespread use, toxicity, and volatility, exposure to formaldehyde is significant consideration for human health.
This chemical is classified as an irritant and a potential cancer-causing hazard. Occupational safetyand health rules establish one part per million for an eight-hour average as the permissible exposure limit. Studies show that levels as high as 10 parts per million have been found in mortuary and funeral home preparation rooms.
To avoid the overexposure of workers to formaldehyde, the preferred method is to provide engineering controls in the workplace environment. This would be some type of mechanical exhaust ventilation system which pulls contaminated air away from an employee's breathing zone and vents it to the outside of the building. If engineering controls are not feasible given a specific work environment, then, at a minimum, employers are required to provide respirators for all workers overexposed to formaldehyde.
In addition, employers are required to take air monitoring samples regularly to determine if overexposures are occurring. If this is the case, the employer must provide medical surveillance or monitoring (periodic physical examinations). Medical surveillance is initiated at the employee's request and paid for by the employer. All air sampling and medical surveillance records must be maintained by the employer for 30 years.
Employers also are required to provide Personal Protection Equipment (PPE) to workers at all times. This includes gloves, chemical goggles, and face shields. In the event that a worker is splashed with formaldehyde and there is direct exposure to the skin and eyes, employers are required to provide (two-jet type) eye washes (plumbed) and quick-drench showers. Both of these must be Immediately available in the area where employees are exposed to chemicals. If a worker is splashed in the eyes with formaldehyde, 15 minutes of flushing with a water-pressure eye wash is necessary. Other chemical hazards found in mortuaries and funeral homes may include industrial cleaning and sterilization products. The same Personal Protective Equipment can be used effectively in the presence of these chemicals.

Health effect of Polychlorinated biphenyl

2009-01-12T19:36:00.000+07:00

The toxicity of PCBs to animals was first noticed in the 1970s when emaciated seabird corpses with very high PCB body burdens washed up on beaches. Since seabirds may die far out at sea and still wash ashore, the true sources of the PCBs were unknown. Where they were found is no reliable indicator of where they had died.

The toxicity of PCBs varies considerably among congeners. The coplanar PCBs, known as non-ortho PCBs because they are not substituted at the ring positions ortho to (next to) the other ring, (i.e. PCBs 77, 126, 169, etc), tend to have dioxin-like properties, and generally are among the most toxic congeners. Because PCBs are almost invariably found in complex mixtures, the concept of toxic equivalency factors (TEFs) has been developed to facilitate risk assessment and regulatory control, where more toxic PCB congeners are assigned higher TEF values. One of the most toxic compounds known, 2,3,7,8-tetrachlorodibenzo[p]dioxin, is assigned a TEF of 1.^[30]

Signs and symptoms

Humans

The most commonly observed health effects in people exposed to extremely high levels of PCBs are skin conditions such as chloracne and rashes, but these were known to be symptoms of acute systemic poisoning dating back to 1922. Studies in workers exposed to PCBs have shown changes in blood and urine that may indicate liver damage. In 1968 in Japan, 280 kg of PCBs contaminated rice bran oil used as chicken feed, resulting in a mass poisoning known as Yushō Disease in over 14,000 people.^[31] Common symptoms included dermal and ocular lesions, irregular menstrual cycles and a lowered immune response.^[32]^[33]^[34] Other symptoms included fatigue, headache, cough, and unusual skin sores.^[35] Additionally, in children, there were reports of poor cognitive development.^[32]^[34]^[35]

There have also been studies of the health effects of PCBs in the general population and in children of mothers who were exposed to PCBs.

Animals

Animals that eat PCB-contaminated food even for short periods of time get liver damage and may die. In 1968 in Japan, 400,000 birds died after eating poultry feed that was contaminated with PCBs.^[31] Animals that eat smaller amounts of PCBs in food over several weeks or months develop various kinds of health effects, including anemia; acne-like skin conditions (chloracne); and liver, stomach, and thyroid gland injuries (including hepatocarcinoma). Other effects of PCBs in animals include changes in the immune system, behavioral alterations, and impaired reproduction. PCBs are not known to cause birth defects in humans, although those that have dioxin-like activity are known to cause a variety of teratogenic effects in animals.

Effects during pregnancy/breastfeeding

Women who were exposed to relatively high levels of PCBs in the workplace or ate large amounts of fish contaminated with PCBs had babies that weighed slightly less than babies from women who did not have these exposures. Babies born to women who ate PCB-contaminated fish also showed abnormal responses in tests of infant behavior. Some of these behaviors, such as problems with motor skills and a decrease in short-term memory, lasted for several years. Other studies suggest that the immune system was affected in children born to and nursed by mothers exposed to increased levels of PCBs. The most likely way infants will be exposed to PCBs is from breast milk. Transplacental transfers of PCBs were also reported.

Studies have shown that PCBs alter estrogen levels in the body and contribute to reproduction problems. In the womb, males can be feminized or the baby may be intersex, neither a male nor a female. Also, both sets of reproductive organs may develop. More instances of this are being reported. Biological magnification of PCBs has also led to polar bears and whales that have both male and female sex organs and males that cannot reproduce. This effect is also known as endocrine disruption. Endocrine Disrupting Chemicals (EDC's) pose a serious threat to reproduction in top-level predators.

Cancer link

A few studies of workers indicate that PCBs were associated with specific kinds of cancer in humans, such as cancer of the liver and biliary tract. Rats that ate food containing high levels of PCBs for two years developed liver cancer. The Department of Health and Human Services (DHHS) has concluded that PCBs may reasonably be anticipated to be carcinogens. The US Environmental Protection Agency (EPA) and the International Agency for Research on Cancer (IARC) have determined that PCBs are probably carcinogenic to humans. PCBs are also classified as probable human carcinogens by the National Cancer Institute, World Health Organization, and the Agency for Toxic Substances and Disease Registry. Recent research by the National Toxicology Program has confirmed that PCB126 (Technical Report 520) and a binary mixture of PCB126 and PCB153 (Technical Report 531) are carcinogens.

Nuclear Reactions

2009-01-08T19:58:00.006+07:00

Many kinds of nuclear reactions occur in response to the absorption of particles such as neutrons or protons. Other types of reactions may involve the absorption of gamma rays or the scattering of gamma rays. Of particular note is the resonant absorption of gamma rays in the Mossbauer effect. Specific nuclear reactions can be written down in a manner similar to chemical reaction equations. If a target nucleus X is bombarded by a particle a and results in a nucleus Y with emitted particle b, this is commonly written in one of two ways.

We can characterize the energetics of the reaction with a reaction energy Q, defined as the energy released in the reaction. The Q is positive if the total mass of the products is less than that of the projectile and target, indicating that the total nuclear binding energy has increased. The probability of a given type of nuclear reaction taking place is often stated as a "cross section".

Some Nuclear Reactions

* The nuclear reaction in the atmosphere which produces carbon-14 for radiocarbon dating.

Data from C. W. Li, W. Whaling, W. A. Fowler, and C. C. Lauritson, Physical Review 83:512 (1951)

Nuclear Cross Section

To characterize the probability that a certain nuclear reaction will take place, it is customary to define an effective size of the nucleus for that reaction, called a cross section. The cross section is defined by

The cross section has the units of area and is on the order of the square of the nuclear radius. A commonly used unit is the barn:

A standard old story was that in the early days of the field, a particular cross section turned out to be much bigger than expected. An experimenter exclaimed "Why, that's as big as a barn!" and a unit name was born.

What is dioxin?

2008-12-24T17:22:00.004+07:00

Dioxins and furans are some of the most toxic chemicals known to science. A draft report released for public comment in September 1994 by the US Environmental Protection Agency clearly describes dioxin as a serious public health threat. The public health impact of dioxin may rival the impact that DDT had on public health in the 1960's. According to the EPA report, not only does there appear to be no "safe" level of exposure to dioxin, but levels of dioxin and dioxin-like chemicals have been found in the general US population that are "at or near levels associated with adverse health effects."

Dioxin is a general term that describes a group of hundreds of chemicals that are highly persistent in the environment. The most toxic compound is 2,3,7,8-tetrachlorodibenzo-p-dioxin or TCDD. The toxicity of other dioxins and chemicals like PCBs that act like dioxin are measured in relation to TCDD. Dioxin is formed as an unintentional by-product of many industrial processes involving chlorine such as waste incineration, chemical and pesticide manufacturing and pulp and paper bleaching. Dioxin was the primary toxic component of Agent Orange, was found at Love Canal in Niagara Falls, NY and was the basis for evacuations at Times Beach, MO and Seveso, Italy.

Dioxin is formed by burning chlorine-based chemical compounds with hydrocarbons. The major source of dioxin in the environment comes from waste-burning incinerators of various sorts and also from backyard burn-barrels. Dioxin pollution is also affiliated with paper mills which use chlorine bleaching in their process and with the production of Polyvinyl Chloride (PVC) plastics and with the production of certain chlorinated chemicals (like many pesticides).

Does dioxin cause cancer?

Yes. The EPA report confirmed that dioxin is a cancer hazard to people. In 1997, the International Agency for Research on Cancer (IARC) -- part of the World Health Organization -- published their research into dioxins and furans and announced on February 14, 1997, that the most potent dioxin, 2,3,7,8-TCDD, is a now considered a Group 1 carcinogen, meaning a "known human carcinogen."

Also, in January 2001, the U.S. National Toxicology Program upgraded 2,3,7,8-TCDD from "Reasonably Anticipated to be a Human Carcinogen" to "Known to be a Human Carcinogen." See their reports on dioxins and furans from their most recent 11th Report on Carcinogens. Finally, a 2003 re-analysis of the cancer risk from dioxin reaffirmed that there is no known "safe dose" or "threshold" below which dioxin will not cause cancer.

A July 2002 study shows dioxin to be related to increased incidence of breast cancer.

Catalysts and Initiators

2008-12-24T17:09:00.000+07:00

Catalysts and initiators start or promote chemical reactions that are used to produce organic chemicals, polymers and adhesives. A chemical catalyst is a substance that increases the rate at which a chemical reaction occurs; however, the catalyst itself does not undergo chemical change. An initiator is a chemical compound that helps start a chemical reaction such as polymerization. Unlike a catalyst, an initiator is usually consumed in the reaction. Substances such as organic peroxides are commonly used as initiators. According to some estimates, more than half of all petrochemical processes use catalysts and initiators. In heterogeneous catalysis, a chemical catalyst provides a surface on which reactants become adsorbed temporarily, and where chemical bonds in the reactants are weakened, allowing new bonds to be created. Because the bonds between the products and the catalyst are weaker, the products are released from the chemical catalyst. Continuous process catalysts (CPC) are used to process industrial chemicals such as solvents, plasticizers, monomers and intermediates. Catalytic solutions include a variety of specialized catalyst products.

There are two basic types of catalysis: homogeneous catalysis, in which both the catalyst and reactants are in the same phase (for example, liquid or gas), and heterogeneous catalysis, in which the catalyst and reactants are in different phases (for example, solid catalysts and gaseous reactants). Metal catalysts and initiators are made from precious metals such as gold, iridium, osmium, palladium, platinum, rhodium, ruthenium and silver. They are used as heterogeneous catalysts for reactions such as hydrogenation and isomerization. Zeolites, minerals with a porous structure, can also be used as catalysts. Synthetic zeolites are the most important catalysts in petrochemical refineries. The proper selection of catalysts and initiators is an important consideration. For example, using rhodium or platinum as catalysts can produce different products depending on whether methane or ethane are used.

ASTM International (formerly called the American Society for Testing and Materials (ASTM), maintains standards for catalysts such as ASTM D3766, standard terminology relating to catalysts and initiators. Some catalysts and initiators must be handled as hazardous materials. The National Fire Protection Association (NFPA) maintains NFPA 432, a standard which covers the catalyst organic peroxide.

Cancer

2008-12-09T18:19:00.001+07:00

Cancer (medical term: malignant neoplasm) is a class of diseases in which a group of cells display uncontrolled growth (division beyond the normal limits), invasion (intrusion on and destruction of adjacent tissues), and sometimes metastasis (spread to other locations in the body via lymph or blood). These three malignant properties of cancers differentiate them from benign tumors, which are self-limited, do not invade or metastasize. Most cancers form a tumor but some, like leukemia, do not. The branch of medicine concerned with the study, diagnosis, treatment, and prevention of cancer is oncology.
Cancer may affect people at all ages, even fetuses, but the risk for most varieties increases with age.[1] Cancer causes about 13% of all deaths.[2] According to the American Cancer Society, 7.6 million people died from cancer in the world during 2007.[3] Cancers can affect all animals.
Nearly all cancers are caused by abnormalities in the genetic material of the transformed cells. These abnormalities may be due to the effects of carcinogens, such as tobacco smoke, radiation, chemicals, or infectious agents. Other cancer-promoting genetic abnormalities may be randomly acquired through errors in DNA replication, or are inherited, and thus present in all cells from birth. The heritability of cancers are usually affected by complex interactions between carcinogens and the host's genome. New aspects of the genetics of cancer pathogenesis, such as DNA methylation, and microRNAs are increasingly recognized as important.
Genetic abnormalities found in cancer typically affect two general classes of genes. Cancer-promoting oncogenes are typically activated in cancer cells, giving those cells new properties, such as hyperactive growth and division, protection against programmed cell death, loss of respect for normal tissue boundaries, and the ability to become established in diverse tissue environments. Tumor suppressor genes are then inactivated in cancer cells, resulting in the loss of normal functions in those cells, such as accurate DNA replication, control over the cell cycle, orientation and adhesion within tissues, and interaction with protective cells of the immune system.
Diagnosis usually requires the histologic examination of a tissue biopsy specimen by a pathologist, although the initial indication of malignancy can be symptoms or radiographic imaging abnormalities. Most cancers can be treated and some cured, depending on the specific type, location, and stage. Once diagnosed, cancer is usually treated with a combination of surgery, chemotherapy and radiotherapy. As research develops, treatments are becoming more specific for different varieties of cancer. There has been significant progress in the development of targeted therapy drugs that act specifically on detectable molecular abnormalities in certain tumors, and which minimize damage to normal cells. The prognosis of cancer patients is most influenced by the type of cancer, as well as the stage, or extent of the disease. In addition, histologic grading and the presence of specific molecular markers can also be useful in establishing prognosis, as well as in determining individual treatments.

Preventing Cancer
Recently, cancer researchers and physicians have devoted time and attention to the preventive aspects of fighting cancer. Early anticancer efforts were directed at treating the disease, but increasingly research has shown that individuals can take steps to prevent cancer. In 1964, the Surgeon General told the country that if we stopped smoking we could greatly reduce our chances of contracting lung cancer. Over the past several decades we have begun to hear other similar messages.
We know that the behavior of the cells in our bodies may be affected by any or all of the following:

Dietary factors
Tobacco use
Environmental agents
Heredity

While there are no absolute guarantees when it comes to preventing cancer, we know—or have good reason to believe—that lifestyle changes can protect you from cancer. These changes include:

Stoping smoking and avoiding "second-hand" smoke.
Eating less fat.
Eating more fiber.
Eating more fruits and vegetables.
Limiting alcohol consumption.
Wearing sunscreen.
Exercising.

In this section of the module we will look at four "risk factors" for cancer: heredity, nutrition, smoking, and exposure to the sun. Use the menu below to begin your tour through the world of cancer prevention.

Water

2008-12-06T18:11:00.003+07:00

Water is the chemical substance with chemical formula H2O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom.
The major chemical and physical properties of water are:
Water is a tasteless, odorless liquid at ambient temperature and pressure. The color of water and ice is, intrinsically, a very light blue hue, although water appears colorless in small quantities. Ice also appears colorless, and water vapor is essentially invisible as a gas.[4]
Water is transparent, and thus aquatic plants can live within the water because sunlight can reach them. Only strong UV light is slightly absorbed.
Since oxygen has a higher electronegativity than hydrogen, water is a polar molecule. The oxygen has a slight negative charge while the hydrogens have a slight positive charge giving the article a strong effective dipole moment. The interactions between the different dipoles of each molecule cause a net attraction force associated with water's high amount of surface tension.
Another very important force that causes the water molecules to stick to one another is the hydrogen bond.[5]
The boiling point of water (and all other liquids) is directly related to the barometric pressure. For example, on the top of Mt. Everest water boils at about 68 °C (154 °F), compared to 100 °C (212 °F) at sea level. Conversely, water deep in the ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid.
Water has a high surface tension caused by the weak interactions, (Van Der Waals Force) between water molecules because it is polar. The apparent elasticity caused by surface tension drives the capillary waves.
Water also has high adhesion properties because of its polar nature.
Capillary action refers to the tendency of water to move up a narrow tube against the force of gravity. This property is relied upon by all vascular plants, such as trees.
Water is a very strong solvent, referred to as the universal solvent, dissolving many types of substances. Substances that will mix well and dissolve in water, e.g. salts, sugars, acids, alkalis, and some gases: especially oxygen, carbon dioxide (carbonation), are known as "hydrophilic" (water-loving) substances, while those that do not mix well with water (e.g. fats and oils), are known as "hydrophobic" (water-fearing) substances.
All the major components in cells (proteins, DNA and polysaccharides) are also dissolved in water.
Pure water has a low electrical conductivity, but this increases significantly upon solvation of a small amount of ionic material such as sodium chloride.
Water has the second highest specific heat capacity of any known chemical compound, after ammonia, as well as a high heat of vaporization (40.65 kJ mol−1), both of which are a result of the extensive hydrogen bonding between its molecules. These two unusual properties allow water to moderate Earth's climate by buffering large fluctuations in temperature.
The maximum density of water is at 3.98 °C (39.16 °F).[6] Water becomes even less dense upon freezing, expanding 9%. This causes an unusual phenomenon: ice floats upon water, and so water organisms can live inside a partly frozen pond because the water on the bottom has a temperature of around 4 °C (39 °F).

ADR label for transporting goods dangerously reactive with water
Water is miscible with many liquids, for example ethanol, in all proportions, forming a single homogeneous liquid. On the other hand, water and most oils are immiscible usually forming layers according to increasing density from the top. As a gas, water vapor is completely miscible with air.
Water forms an azeotrope with many other solvents.
Water can be split by electrolysis into hydrogen and oxygen.
As an oxide of hydrogen, water is formed when hydrogen or hydrogen-containing compounds burn or react with oxygen or oxygen-containing compounds. Water is not a fuel, it is an end-product of the combustion of hydrogen. The energy required to split water into hydrogen and oxygen by electrolysis or any other means is greater than the energy released when the hydrogen and oxygen recombine.[7]
Elements which are more electropositive than hydrogen such as lithium, sodium, calcium, potassium and caesium displace hydrogen from water, forming hydroxides. Being a flammable gas, the hydrogen given off is dangerous and the reaction of water with the more electropositive of these elements is violently explosive.

Overview of Chemistry

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Chemistry is the scientific study of interaction of chemical substances [3] that are constituted of atoms or the subatomic particles: protons, electrons and neutrons.[4] Atoms combine to produce molecules or crystals. Chemistry is often called "the central science" because it connects the other natural sciences, such as astronomy, physics, material science, biology, and geology.[5][6]
The genesis of chemistry can be traced to certain practices, known as alchemy, which had been practiced for several millennia in various parts of the world, particularly the Middle East.[7]
The structure of objects we commonly use and the properties of the matter we commonly interact with, are a consequence of the properties of chemical substances and their interactions. For example, steel is harder than iron because its atoms are bound together in a more rigid crystalline lattice; wood burns or undergoes rapid oxidation because it can react spontaneously with oxygen in a chemical reaction above a certain temperature; sugar and salt dissolve in water because their molecular/ionic properties are such that dissolution is preferred under the ambient conditions.
The transformations that are studied in chemistry are a result of interaction either between different chemical substances or between matter and energy. Traditional chemistry involves study of interactions between substances in a chemistry laboratory using various forms of laboratory glassware.

Laboratory, Institute of Biochemistry, University of Cologne
A chemical reaction is a transformation of some substances into one or more other substances.[8] It can be symbolically depicted through a chemical equation. The number of atoms on the left and the right in the equation for a chemical transformation is most often equal. The nature of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws.
Energy and entropy considerations are invariably important in almost all chemical studies. Chemical substances are classified in terms of their structure, phase as well as their chemical compositions. They can be analysed using the tools of chemical analysis, e.g. spectroscopy and chromatography.
Chemistry is an integral part of the science curriculum both at the high school as well as the early college level. At these levels, it is often called 'general chemistry' which is an introduction to a wide variety of fundamental concepts that enable the student to acquire tools and skills useful at the advanced levels, whereby chemistry is invariably studied in any of its various sub-disciplines. Scientists, engaged in chemical research are known as chemists.[9] Most chemists specialize in one or more sub-disciplines.