Contaminant Sources

Airborne contaminant movement in the building depends upon the type of heat and contaminant sources, which can be classified as (1) buoyant (e.g., heat) sources, (2) nonbuoyant (diffusion) sources, and (d) dynamic sources.- With the first type of sources, contaminants move in the space primarily due to the heat energy as buoyant plumes over the heated surfaces. The second type of sources is characterized by cimtaminant diffusion in the room in all directions due to the concentration gradient in all directions (e.g., in the case of emission from painted surfaces). The emission rare in this case is significantly affected by the intensity of the ambient air turbulence and air velocity, dhe third type of sources is characterized by contaminant movement in the space with an air jet (e.g., linear jet over the tank with a push-pull ventilation), or particle flow (e.g., from a grinding wheel). In some cases, the above factors influencing contaminant distribution in the room are combined. 

There are many peer-review publications reporting NoV outbreaks due to food and water. In spite of a recognized publication bias toward these outbreaks, there is a consensus that the scientific literature imder-estimates the contribution of NoV to food and waterborne disease (Efall et al., 2005 Hoffmann et al., 2007 O Brien et al., 2006). Source contamination of food and water is clearly implicated in NoV outbreaks around the world. 

Before and after the acquisition time, the effluent flow is directed to waste to minimize MS source contamination. 

Magnetic sector mass spectrometers accelerate ions to more than 100 times the kinetic energy of ions analysed in quadrupole and ion trap mass spectrometers. The higher accelerating voltage contributes to the fact that ion source contamination is less likely to result in degraded sensitivity. This is particularly important for analysis that requires stable quantitative accuracy. 

Macdonald, C.R. and C.D. Metcalfe. 1989. A comparison of PCB congener distributions in two point-source contaminated lakes and one uncontaminated lake in Ontario. Water Pollut. Res. Jour. Canada 24 23-46. 

The most straightforward tool for the introduction of a sample into a mass spectrometer is called the direct inlet system. It consists of a metal probe (sample rod) with a heater on its tip. The sample is inserted into a cmcible made of glass, metal, or silica, which is secured at the heated tip. The probe is introduced into the ion source through a vacuum lock. Since the pressure in the ion source is 10-5 to 10-6 torr, while the sample may be heated up to 400°C, quite a lot of organic compounds may be vaporized and analyzed. Very often there is no need to heat the sample, as the vapor pressure of an analyte in a vacuum is sufficient to record a reasonable mass spectrum. If an analyte is too volatile the cmcible may be cooled rather than heated. There are two main disadvantages of this system. If a sample contains more than one compound with close volatilities, the recorded spectrum will be a superposition of spectra of individual compounds. This phenomenon may significantly complicate the identification (both manual and computerized). Another drawback deals with the possibility of introducing too much sample. This may lead to a drop in pressure, ion-molecule reactions, poor quality of spectra, and source contamination. 

Figure 7.5. Point source contamination with transects and varying levels of contamination. 

Describe the differences in sampling procedures that would be used when sampling point source and nonpoint source contaminations. Are there any methods of analysis that would be common to both situations ... 

Fig. 5.15. Sample vial filled with analyte. The bright spot halfway between the tip of the tweezers and upper rim of the vial is the piece of solid material to be analyzed. Use of more sample does not have any advantage it only causes ion source contamination.

Occupational exposure to higher than background levels of chloroform can be expected to occur in some occupations although few quantitative exposure data were located. Populations with the highest potential exposures appear to be workers employed in or persons living near industries and facilities that manufacture or use chloroform operators and individuals who live near municipal and industrial waste water treatment plants and incinerators, and paper and pulp plants and persons who derive their drinking water from groundwater sources contaminated with leachate from hazardous waste sites. 

Organic contaminants can be released to the surface in different ways, and contamination can be classified as point source and nonpoint source (or diffuse source). As an example of a nonpoint source, we discuss the case of pesticides applied during agricultural activity over large areas an example of point source contamination is given by the behavior of petroleum products that reach the subsurface as a result of leakage (or a spill) from pipes or from a gas station. 

Non-volatile buffers such as phosphates, borates, perchlorates and phosphoric acid should be avoided at all costs because of high background ion current, source contamination and blockages, and in the case of perchlorates, explosions. Figure 6.4 shows the mass spectrum of typical background when using phosphoric acid in the eluent. If the solvent system for a particular analysis does not assist the electrospray process, it is possible to enhance ionisation by postcolumn addition of a suitable volatile buffer. 

Great care must be exercised when dealing with compounds that may decompose, so as to minimize the degree of source contamination. As indicated earlier, organometallics are no worse than any other type of compound, and we have direct evidence of this with our double-beam... 

Source contaminates some fish (e.g. tuna, shark, pike)... 

Pereira WE, Hostettler FD. 1993. Nonpoint source contamination of the Mississippi River and its tributaries by herbicides. Environ Sci Technol 27(8) 1542-1552. 

Calibrants are required to calibrate the mass scale of any mass spectrometer, and it is important to find reference compounds that are compatible with a particular ion source. Calibrants commonly used in electron ionization (El) and chemical ionization (Cl), such as perfluorocarbons, are not applicable in the ESI mode. The right calibrants for LC-ESI-MS should (1) not give memory effects (2) not cause source contamination through the introduction of nonvolatile material (3) be applicable in both positive- and negative-ion mode. The main calibrants used or still in use to calibrate ESI-MS can be divided into the following categories polymers, perfluoroalkyl triazines, proteins, alkali metal salt clusters, polyethers, water clusters, and acetate salts. 

Water Cluster. Numerous groups have used water clusters successfully as calibration solutions [10,11,20-22]. Water clusters do not produce any source contamination in ESI-MS and provide closely spaced reference peaks with a calibration range up to m lz 1000. In positive-ion mode, protonated water clusters with up to 70 water molecules are observed. In negative ESI singly deprotonated water clusters are observed [OH (HjO), with n > 20], as well as solvated electrons [(H20)m with m > 11]. 

The new MSPs (Figs. 12.1 and 12.2) offer some advantages over heparin. They show considerably low contamination levels of virus and/or prions because they are exclusively extracted from marine sources. Contamination in clinical solutions of heparin can occur more easily, as this compound is extracted from mammalian sources, like porcine and bovine intestinal mucosa and bovine lung (Mourao, 2004). Moreover, the invertebrate MSPs are promising to be more useful clinical reagents than algal... 

Mills, M.S. and E.M. Thurman (1994a). Reduction of nonpoint source contamination of surface water and groundwater by starch encapsulation of herbicides. Environ. Sci. Technol., 28 73-79. 

It is hypothesized that the DAR may be an indicator of point-source versus nonpoint-source contamination of groundwater by atrazine (Adams and Thurman, 1991). The DAR hypothesis is predicated on the assumption that atrazine degrades slowly in an aquifer because of low organic carbon concentrations, small microbial populations, and anaerobic conditions. This is substantiated by Wehtje et al. (1983) who determined that, under aquifer conditions, atrazine did not undergo deethylation or deisopropylation, and only slowly underwent abiotic degradation to... 

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