Example of Probabilistic Risk Assessment Results

Such approaches can also be used for ecological risk assessment, which has higher levels of uncertainty in the risk estimates due to the lower amount of information on chemical exposure patterns by wildlife. Such approaches will likely not replace the deterministic methods of conducting risk assessment, but their utility lies in identifying how protective a concentration is likely to be under likely exposure conditions. Armed with this knowledge, regulatory agencies are better able to identify 

Sources of chemical contributions to indoor air can come from ambient air through open windows and through the HVAC system. However, this is usually a minor component of indoor air contamination, becanse the amount of air entering a structure from outside is usually small relative to the amount of air in the structure. Other sources of chemicals to indoor air include household cleaners and furniture. New furniture and carpeting contains formaldehyde, a solvent that volatilizes into indoor air. Several other volatile organic compounds (VOCs) are common sonrces of chemicals in indoor air, as shown in table 10.3. 

This example illustrates several things (1) long-term exposure can lead to effects where short-term exposure to the same chemical at the same concentration may not, (2) indoor air quality can adversely affect health, and (3) national regulations are not consistent with regard to protecting indoor air quality. 

In addition to these common sources from consumer products, chemicals can also volatilize from the soil and groundwater beneath structures into indoor air, as shown in figure 10.6. These volatile chemicals are present in the subsurface from releases associated with industrial activities, including leaking underground fuel tanks (e.g., benzene, MTBE, and other petroleum-related chemicals), surface spills (followed by downward percolation of chemicals to groundwater and lateral transport beneath structures), and other environmental releases. 

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Figure 10.5. Example of Probabilistic Risk Assessment Results...

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