Asbestos concentration-dependent effects

The major sources of air pollutants found in buildings are described below. However, the mere presence of a potential contaminant source does not necessarily mean that exposure will ensue. This is because the extent of exposure, if any, often depends on the physical nature of a source or the manner in which it is used an example of this is asbestos, as will be discussed later. Furthermore, the health significance of exposure to indoor pollutants may not always be clear. While many of these toxicants may have adverse effects under exposure conditions found in occupational and other environments, often much less is known about biological responses with prolonged exposures at concentrations common in indoor environments. 

People exposed to PAHs in conjunction with particulates from tobacco smoke, fossil-fuel combustion, coal fly ash, and asbestos fibers are at increased risk of developing toxic effects, primarily cancer. Even people not susceptible to the toxic effects of PAHs may become affected when exposure occurs in conjunction with exposure to particulates (NRC 1983). This enhanced effect results from the adsorption of PAHs onto the particulates. They are vacuolized into cells, and distributed differently in tissues depending on the size and type of particulate matter. This increased PAH uptake may result in more efficient induction of AHH activity at low PAH concentrations. This activity also increases the dose to the gastrointestinal tract as a result of mucocilliary clearance (NRC 1983). This synergistic action between PAHs and particulate matter in air pollution has been associated with the occurrence of stomach cancer in humans (Fraumeni 1975). 

Equipment for impregnating asbestos is conceptually similar to those used for glass cloth coating. Asbestos readily picks up PTFE dispersions and the amount of uptake depends on the concentration of PTFE in the dip tank. The dispersion may be diluted moderately with deionized water or substantially using a dilute aqueous solution of a nonionic surfactant such as Triton X-100. The speed of the asbestos yam movement through the dip tank has little effect on the amount of uptake. The length and capacity of the oven determines the maximum throughput of the process. 

The fillers could be used up to about 60 phr and higher concentrations are sometimes used where the application permits. Asbestos and whiting may sometimes be used more than 1(X) phr. Evaluation of the effect of various fillers on the physical properties of the compound are complicated and depends on the other ingredients of the compounds (48). 

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