Models elevated contamination

As a result of volatilization, significantly elevated indoor air levels of trichloroethylene can occur in homes that use water supplies contaminated with trichloroethylene (Andelman 1985a). The transfer of trichloroethylene from shower water to air in one study had a mean efficiency of 61% which was independent of water temperature (McKone and Knezovich 1991). The study authors concluded that showering for 10 minutes in water contaminated with trichloroethylene could result in a daily exposure by inhalation comparable to that expected by drinking contaminated tap water. Another study using a model shower system found that, in addition to shower spray, shower water collecting around the drain could be an important source of volatilized trichloroethylene, and the fraction volatilized could be affected by spray drop size and flow rate (Giardino et al. 1992). 

Perhaps the most tedious and mundane aspect in the development and validation of an atmospheric simulation model is the compilation of a complete contaminant emissions inventory. Yet, such an inventory must be made before a model can be validated since the spatial and temporal distribution of contaminant emissions comprises a direct input to the overall simulation model. Ground-level sources enter into the boundary conditions of the conservation equations through the function Qi y t) introduced previously elevated sources enter as Si x,y,z,t) in the conservation equations themselves. 

Italian monitoring data of freshwater samples related to pesticide contamination in 1997 are reported in Table 7. The pesticides are listed in a decreasing order in respea to Priority Index (P.I.)> an index calculated on the basis of pesticide sold quantity, of the field application rates and of the water repartition evaluated with the Mackay model. In Table 7, the percent of laboratories that searched pesticides (%R) and the percent of positive samples (%P) are also showed. It is evident that the monitoring of some pesticides is very poor, even if they have an elevate P.I. Some active ingredients, like metolachlor and terbuthylazine, are contaminants widespread in freshwaters. 

Since a power-assisted air-purifying (PAAP) respirator is a positive-pressure system, i.e., the air within the facepiece is atahigherpressure than the outside air, this type of unit intrinsically provides more protection than the ordinary half-face respirator. If provision is made for an escape mode of operation, i.e., the wearer can continue to breathe through the filters should the pump fail, and escape from the contaminated atmosphere. The ANSI Z88.2 standard (AmericanNational Standard Institute) would permit the use ofthis type ofrespiratorin an IDLH atmosphere. Some ofthe early models of this type of unit had some problems with the seals on the pumps, but these problems have been corrected and they represent a desirable alternative if the wearer is to remain in a contaminated atmosphere for extended periods. There have been a few problems with the pumps overheating while being used at elevated temperatures. 

Several dispersion models have been developed. These models are mathematical descriptions (equations) of the meteorological transport and dispersion of air contaminants in a particular area that allow estimates of contaminant concentrations, either at ground level or elevated (Carson and Moses, 1969). User-friendly modeling programs are available now that produce quick, accurate results from the operator s pertinent data. 

In areas that are significantly contaminated with radionuclides or in areas with elevated rates of transfer of radionuclides from soil to biota, whole body measurement techniques can be applied to determine the human body burden and to assess doses due to the internal exposure of critical groups. Seasonal variations in the content of some radionuclides in the human body should be taken into account when assessing annual doses on the basis of particular whole body measurements. The results of individual measurements should be used mainly for validation of the models applied for the purposes of internal dose assessment. 

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