Chemical contaminants

A.irbome Basic Chemical Contamination. A critical, and at-first pu22ling problem, was encountered during early manufacturing trials of CA resists. Sporadically, severely distorted resist profiles would be formed in positive-tone CA resists, displaying what seemed to be a cap on the upper surface of the resist image (Fig. 26). In severe cases this cap or T-top would appear as a kin or cmst over the entire wafer surface that prevented development of the pattern. The magnitude of the effect varied dramatically between laboratories and appeared to grow more severe as the time interval between exposure and post-exposure bake was increased. 

Fig. 26. SEM micrographs illustratiag the effects of airborne basic chemical contamination, (a) This image was formed when a positive-tone CA resist was processed without any delay after coating, (b) This image was formed when an identical film was stored after coating for 15 minutes in an atmosphere containing 10 parts per billion on A/-methylpyrrohdone, and then processed identically to the first film.

Contamination. Manufacturers of cosmetics must be careful to guard against chemical and microbial contamination. Chemical contamination, which may result from the presence of undesirable impurities in raw materials, is avoidable by adhering to rigid specifications for raw materials. Compendial specifications and pubHcations by the CTFA and other professional societies form the basis of most intracompany raw material specifications. Moreover, all packaging components must meet not only physical and design specifications but also such chemical requirements as extractables and absence of dust and similar contaminants (see Packaging, cosLffiTics and pharmaceuticals). 

An entirely different type of contamination arises from the presence of microbiota in a product. As in the case of chemical contamination, compendial requirements for microbiological purity exists. Pharmacopoeial standards vary from country to country, and manufacturers must use the specifications and kill times that meet local requirements. As of this writing, the criteria in the British Pharmacopoeia are more stringent than those estabUshed by the CTFA, which are stricter than those in the United States Pharmacopoeia. In order to meet commonly accepted standards of microbial purity, manufacturing faciUties must be periodically cleaned and all products that can support microbial growth must contain an effective preservative (6). 

Many of the fabrication processes for iategrated circuits are similar or coaceptuaHy related to those used ia the manufacture of ptinted wiring boards. However, because of the extremely fine device features, fabrication must be carried out ia clean rooms having strictly controlled environments. Particulate and chemical contamination are minimized, and temperature, humidity, and even vibration are carefully controlled. 

A number of airborne chemical contaminants are EDs, particularly products of combustion such as dioxins and polycyclic aromatic hydrocarbons. ... 

Chemical-mediated immune suppression has been identified from the experimental study of several wildlife species. Harbour seals fed either chemically contaminated fish from the Wadden Sea or imcontaminated fish were found to have differing immune responses, with the exposed group showing lowered immune response to microbial infections and certain types of cancer. "" Mink fed fish taken from below a discharge point for bleached Kraft pulp mill effluent have also shown impaired immune function, " showing that the non-accnmillative chemicals in this effluent can actively disrupt endocrine associated functions. 

These transformers may be PVC taped, thermoplastic (polypropylene) moulded, fibreglass taped, polyester resin cast or epoxy resin cast depending upon the system voltage and the surroundings. HT indoor transformers, for instance, are generally polyester or epoxy resin cast, and are economical with good dielectric properties. They are resistant to humid, chemically contaminated and hazardous areas. Outdoor HT transformers, how-ever. may be epoxy... 

The ground conductor can be of aluminium, GI or copper, as discussed earlier. A humid or a chemically contaminated location is corroding in nature. Aluminium has a rapid reaction and is fast corroding. At such locations, use of GI or copper conductor would be more appropriate. Table 22.4 suggests the ground conductor sizes for aluminium conductor power cable.s for small and medium-ratine feeders when aluminium is used for the ground... 

Chemical. Where severe chemical contamination is suspected, specific precautions must be followed if OSH A action levels are approached. Such instances rarely occur in LAQ investigations. One possible exception might be a pesticide spill in a confined space. In this case, an appropriate respirator and disposable coveralls may be needed. 

The reaction mechanism depends on the chemistry of the active oxidant and chemical contaminants. Multiple sequential and parallel reaction steps occur frequently. Partial oxidation produces noxious byproducts. 

Chemical Contaminants (Carcinogens) If there is evidenee that a chemical may cause eancer, and there is no dose below which the chemieal is considered safe, the MCLG is set at zero. If a chemieal is carcinogenie and a safe dose can be deter mined, the MCLG is set at a level above zero that is safe. 

Granular media filtration is used for treating aqueous waste streams. The filter media consists of a bed of granular particles (typically sand or sand with anthracite or coal). The anthracite has adsorptive characteristics and hence can be beneficial in removing some biological and chemical contaminants in the wastewater. This material may also be substituted for activated charcoal. 

Testing for the presence of permeated chemical contaminants requires that pieces (in the case of contaminated soil this would be typically those that visually indicate contamination) of the protective garments be sent to a laboratory for analysis. 

The working environment may need to be controlled, not for the benefit of the staff but to achieve the required characteristics. To achieve high performance from electronic components, particle and chemical contamination has to be minimized during fabrication and assembly. For these and many other reasons, the production environment may need to be controlled. If these conditions apply you should ... 

CCC - Comprehensive Chemical Contaminant Series, 304 CCINFO MSDS Series - Canadian Centre for Occupational Health and Safety, 304 CCM Chemicals Sdn Bird, 191 CCNU, 37... 

In the past the presence of hazardous substances in soils was not a major public concern. In spite of the large number of documented hazardous waste sites in the United States, relatively few sites liave been cleaned up widi specific redevelopment in mind. Remedial actions usually are undertaken to contain or remove chemical contaminants little or no consideration is given to the ultimate use of the site. If land reuse is decided before the cleanup there may be an opportunity to tailor the cleanup acti ities to best suit the site rcde elopment. 

Overhead transmission lines require that the area beneath them be cleared of trees or tall shrubs, which may result in erosion. When the transmission line right-of-way is not kept clear, the transmission line may come into contact with vegetation, causing a fault on the system and possibly starting a fire. Chemical contamination of soil may result from some types of transmission structures, such as treated wood. Burial of underground cables also can impact the environment due to erosion. 

Extending the inteiwal between oil changes in automobiles and machinery is another way to conserve lubricants. Oil life is limited by depletion of oil additives, overheating, chemical contamination, and contamination of the oil by foreign particles. Using improved additives and filtering of particles, oil life can be considerably extended. 

The surface mud system is designed to restore the mud to the required properties before it is pumped downhole. Most of the equipment is used for solids removal only a small part of the surface mud system is designed to treat chemical contamination of the mud. There are three basic means of removing drilled solids from the mud dilution-discard, chemical treatment, and mechanical removal. 

Surface finish is increasingly referred to as surface cleanliness . This can be misleading because the standards refer to the appearance of the blasted steel and do not deal with chemical contamination. Site tests for assessing the level of soluble salts on freshly blast-cleaned surfaces, and which allow the semi-quantitative determination of the chlorides, soluble sulphates and soluble iron salts, are urgently needed. 

Cells and isolated enzymes are often susceptible to poisoning at low levels of chemical contamination. It is, therefore, necessary to carry out expensive purification of substrates (feedstocks) and water used in bioprocesses. 

Costs of downstream processing for purely chemical synthesis would be increased by 1) low specificity of reactions (giving rise to chemical contaminants closely related to the desired product) and 2) the toxic/corrosive nature of the chemicals. 

Golberg, L., Trace chemical contaminants in food potential for harm, ... 

Barbash J, Roberts PV. 1986. Volatile organic chemical contamination of groundwater resources in the U.S. J Water Pollut Control Fed 58 343-348. 

Kilbum KH, Warshaw RH. 1993. Effects on neurobehavioral performance of chronic exposure to chemically contaminated well water. Toxicol Ind Health 9 391 -404. 

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