Sources of contamination

Various pesticides - including organochlorines, which are very persistent in the environment - are used in agriculture and forestry to control pests. For example, chlordane and heptachlor have been banned since 1988 in many parts of the world, but they are still present in the environment. Some authors have reported the volatilization of these organochlorines and their metabolites, which has resulted in the contamination of the atmosphere [11-13]. These authors have made claims about the volatilization of chlordane, heptachlor and heptachlor exo-epoxide pesticides, which have accumulated in the atmosphere. They have also reported that the spray, used to control termites, is the main cause of the atmospheric contamination in the southern United States. 

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The primary sources of contamination in ion implantation come from metal atoms that may be etched off reactor fixtures, such as reactor wads, wafer holder, cHps, and so on. The pump oils used by the vacuum pumps may be a source of hydrocarbon contamination. The dopant sources themselves are not a significant source of contamination because unwanted ions are separated out from the beam during beam analysis. 

A knowledge of the molecular composition of a petroleum also allows environmentalists to consider the biological impact of environmental exposure. Increasingly, petroleum is being produced in and transported from remote areas of the world to refineries located closer to markets. Although only a minuscule fraction of that oil is released into the environment, the sheer volume involved has the potential for environmental damage. Molecular composition can not only identify the sources of contamination but also aids in understanding the fate and effects of the potentially hazardous components (7). 

Carbon produced by these latter reactions is formed in the catalyst pores, making it much more difficult to remove, and potentially causing physical breakage. Operating steam to carbon ratios are chosen above the minimum required in order to make carbon formation by these reactions thermodynamically impossible (3). Steam is another potential source of contaminants. Chemicals from the boiler feedwater or the cooling system are poisons to the reformer catalyst, so steam quality must be carefully monitored. 

To meet the cleanliness need, all elements of the process are controlled to minimize sources of contamination. Air normally contains a large volume of contaminants in the form of dirt, dust, and poUen. The human body sheds a large volume of particulate contaminants such as skin, phlegm, hair, etc. 

Contamination of Product This has been partially covered under Cleaning and Equipment Wear. Other sources of contamination are lubricants and repair materials. TApes which are not compatible with the batches to be mixed shoiild be avoided. 

Some of the more obvious sources of contamination of solvents arise from storage in metal drums and plastic containers, and from contact with grease and screw caps. Many solvents contain water. Others have traces of acidic materials such as hydrochloric acid in chloroform. In both cases this leads to corrosion of the drum and contamination of the solvent by traces of metal ions, especially Fe. Grease, for example on stopcocks of separating funnels and other apparatus, e.g. greased ground joints, is also likely to contaminate solvents during extractions and chemical manipulation. 

The greatest source of contamination is extraneous matter. Atmospheric dirt, for example, is always a serious threat. It can enter the oil system through vents, breathers, and seals. Its primary effect is equipment wear, but plugging of oil lines and ports, and reduced oxidation stability of the oil are also serious effects. 

Water contamination in the oil system can cause serious damage to turbomachinery, and every reasonable effort should be made to, first, prevent its entrance into the system, and second, provide suitable removal equipment if water cannot be effectively kept out. Experience indicates that designers and equipment operators can be more effective in keeping water out of the system. Since the main sources of contamination are atmospheric condensation, steam leaks, and faulty oil coolers, preventive measures should be taken. 

Foaming is usually caused by contamination of glycol with salt, hydrocarbons, dust, mud, and corrosion inhibitors. Remove the source of contamination with effective gas cleaning ahead of the absorber, improved solids filtration, and carbon purification. 

Source there is a source of contamination or discomfort indoors, outdoors, or within the mechanical systems of the building. 

All efforts to prevent or correct LAQ problems should include an effort to identify and control pollutant sources. Source control is generally the most cost effective approach to mitigating LAQ problems in which point sources of contaminants can be identified. In the case of a strong source, source control may be the only solution that will work. The following are categories and examples of source control ... 

Examine your building operation. Make an inventory list of all the sources of contaminants that impact on indoor air quality. Determine whieh among these are likely to have first order effects on air quality. 

Microorganisms MCLG (mg/L) MCL or TTi (mg/L) Potential Health Effects from Ingestion of Water Sources of Contaminant in Drmking Water... 

For most hazardous waste sites with proper planning the situation is known before remediation activities begin. The support zone location needs to be carefully considered at the planning stages of the project. A better solution to the theoretical problem at hand would be to move the support zone further from the source of contamination. If the support zone can be placed far enough away, the likelihood for exposure at the support zone is minimized. 

However, moving the support zone farther from the source of contamination often brings up logistical problems associated with the distance. The logistics should be considered at all times. No matter how open the space is, there are always distance constraints. 

Encasing the source of contaminants with, for example, plastic sheeting or overpacks [2]. 

This section discusses primarily internal sources of contaminants and other occupational hazards related to the process or the building envelope. 

The pollutant-capturing efficiency of local ventilation systems depends on hood design, the hood s positioning near the source of contamination, and the... 

Rim exhausts are suitable for area sources of contaminant. They are limited in the area over which they can draw with adequate velocity. In practice, the slot hood should be within 0.6 m of the far edge of the source. For an open surface tank this means that a slot hood on one long side is necessary for tanks up to 0.6 m in width hoods on both long sides are necessary for tanks up to 1.2 m in width and rim exhaust is not practical for tanks wider than 1.2 m. For those situations, push-pull ventilation or enclosure type hoods are recommended.- ... 

Another design method uses capture efficiency. There are fewer models for capture efficiency available and none that have been validated over a wide range of conditions. Conroy and Ellenbecker - developed a semi-empirical capture efficiency for flanged slot hoods and point and area sources of contaminant. The point source model uses potential flow theory to describe the flow field in front of a flanged elliptical opening and an empirical factor to describe the turbulent diffusion of contaminant around streamlines. 

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