Asbestos toxic properties

Traditionally, hood interiors were made from asbestos sheets, which had both good chemical and good heat resistance. Their main problem was that they absorbed any liquid that was spilled on them. Asbestos has now lost its favor because of its toxic properties. Modem hoods usually have interiors of highly resistant plastic, often fiberglass reinforced. Such surfaces are easy to keep clean, but their temperature resistance may be limited. 

Carbon nanotubes (CNTs) currently attract intense interest because of their unique properties which make them suitable for many industrial applications.28 Carbon nanotubes exhibit some of the properties implied in asbestos toxicity. Carbon nanotubes share with asbestos the fibrous habit - long fibers with a diameter of a few nanometers -and a very high biopersistence. On this basis they are suspected to be hazardous and indeed the first studies in vivo14,29,30 have shown an inflammatory response followed by some evolution towards fibrosis. When inhaled, CNTs may thus constitute a possible hazard to human health. The inflammatory and fibrotic responses elicited by CNTs is similar to that caused by other toxic particles which might be the result of oxidative stress caused by particle- and/or cell-derived free radicals. There is no direct experimental evidence of a capacity of carbon nanotubes to generate free radicals similar to silica asbestos and nano sized iron oxide particles. 

A number of physical and chemical properties such as fiber size, durability, and iron content are important determinants of asbestos toxicity. The dependence of toxicity on these fiber properties is discussed below. 

Silicone rubbers bum if the temperature of the flames exceeds 600-700 °C. However, their combustion does not release toxic products, and there is an isolating layer of carbon dioxide on the product. If this rubber is sealed in a glass or asbestos shell, the cable can endure operating voltage and ensure normal functioning of the electric circuit even in a fire. These properties help to reduce the requirement for wires and cables in most cases by 20% and noticeably increase the safety of operation in case of overloads and fires. 

Aluminas used in chromatography or as catalyst supports are prepared by heating hydrated oxide to various temperatures so that the surfaces may be partially or wholly dehydrated. The activity of the alumina depends critically on the treatment, subsequent exposure to moist air, and other factors. Concentrated aqueous A1C13 solutions can be spun into fibers which on drying produce filaments of A1203. They are non-toxic, unlike asbestos, possess excellent heat insulation properties, and are stable up to 1400°C. 

The potential for unusual health effects of chemical mixtures due to the interaction of chemicals or their metabolites (e.g., metabolites of trichloroethylene and benzene) in or with the biosystem constitutes a real issue in the public health arena. However, toxicity testing to predict effects on humans has traditionally studied one chemical at a time for various reasons convenient to handle, physiochemical properties readily defined, dosage could easily be controlled, biologic fate could easily be measured, and relevant data were often available from human occupational exposures. Chemicals are known to cause disease for example, arsenic and skin cancer, asbestos and lung cancer, lead and decrements of IQ, and hepatitis B predisposes to aflatoxin-induced liver cancer but the link between the extent of human exposure to even well-defined chemical mixtures and disease formation remains relatively unexplored, but of paramount importance to public health. 

The chemicals leached from these surfaces depend on the corrosive properties of the particular water as well as the chemical nature of the surface. Hard water tends to deposit a mineral layer on the inside of pipes and on other surfaces that essentially limits the access of water to the surfaces. On the other hand, soft water, particularly at lower pHs, can actively dissolve toxic metals such as lead or cadmium from pipes or solder. Copper in pipes is also frequently leached from pipes at high concentrations when the water has corrosive properties. Asbestos-cement has been used widely in water mains. The extraction of the asbestos fibers from these surfaces is also very much increased at lower pH and with soft water. The use of lead pipe and solder in household pipes has pretty much been abandoned in the United States. However, alloys of lead are still utilized in many faucets and brass fixtures (e.g., submersible pumps). Rather high concentrations of lead can result if water stands in these fixtures overnight. As a result it is always wise to avoid using the water first drawn from the tap in the morning for human consumption. Low levels of lead exposure in utero or in the first few years of life have been associated with delayed CNS development in humans and experimental animals. 

There have been extensive studies in recent years to understand the toxicity and carcinogenic properties of asbestos fibers and the mechanism of such actions. Among the factors that contribute to the health hazard from exposure to asbestos particles, the route of entry probably is most important. Asbestos fibers in food or drinking water do not seem... 

The toxicity of nanomaterials is not well understood, and many commentators have expressed concern that the unique properties of nanomaterials maybe associated with unknown risks. Some of the concern is because of the ability of small particles to penetrate Hving tissue. There are conflicting study conclusions on whether inhaled nanoparticles may mimic the action of asbestos in the lungs. Some studies conclude that they do cause inflammation because they can reach the lung structures that exchange oxygen and carbon dioxide from the blood. However, other studies conclude that the results are equivocal. Similarly, titanium dioxide nanoparticles have been the subject of several studies to determine whether or not they can penetrate human skin when they are used in sunscreen formulations. While studies have shown that they do not penetrate beyond the outer layer of skin, the studies have been criticized because they were aU on intact, unabraded healthy adult skin, and so the risks in actual use may not be the same as indicated by those studies. In addition, many formulations contain moisturizers that are designed to penetrate skin, and the effects of these moisturizers on the skin penetration of titanium dioxide nanoparticles are unknown. ... 

Polychlorinated biphenyls have very high chemical, thermal, and biological stability low vapor pressure and high dielectric constants. These properties have led to the use of PCBs as coolant-insulation fluids in transformers and capacitors for the impregnation of cotton and asbestos as plasticizers and as additives to some epoxy paints. The same properties that made extraordinarily stable PCBs so useful also contributed to the widespread dispersion and accumulation of these substances in the environment. By regulations issued in the United States under the authority of the Toxic Substances Control Act passed in 1976, the manufacture of PCBs was discontinued in the United States, and their uses and disposal were strictly controlled. Some degree of biodegradation of PCBs in the environment does occur. 

It has been my steadfast conviction from the time I first conceived of phosphate fibers that they are a product that requires no toxicological study. This is the driving force that caused me to initiate the project in the first place. If the fibers are not obviously safe, it made no sense to begin a project. Fibers of phosphate are not new and have been used in all manner of household and industrial products for several lifetimes. They have never caused any toxic problems for people, animals, or vegetation. Literature mentions were made that many phosphates were fibrous and resemble chrysotile in appearance. No use had ever been made of their fiber properties. As long as they were merely being eaten, drunk, and inhaled, no notice was taken of the fact that they were fibrous. It was only when they were to become a safe replacement for asbestos that their safety was questioned. The same is true again today we continue to eat, drink, and breathe phosphates and no one questions their safety. 

Another concern for in vivo use of carbon nanotube-based sensors is their toxicity. Even carbon nanotube toxicity has not yet been fully characterized many present studies find that CNTs aggregate together, generally in the liver, spleen, and lung tissue. CNT aggregates might have similar carcinogenic properties to asbestos fibers. ... 

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