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Linear dose-response assessment
If the "mode of action" information (discussed above) suggests that the toxicity does not have a threshold, then this type of assessment is referred to by the Agency as a "linear" dose-response assessment. In the case of carcinogens, if "mode of action" information is insufficient, then linear extrapolation is typically used as the default approach for dose-response assessment (for more detailed information, please see EPA’s Guidelines for Carcinogen Risk Assessment). In this type of assessment, there is theoretically no level of exposure for such a chemical that does not pose a small, but finite, probability of generating a carcinogenic response. The extrapolation phase of this type of assessment does not use UFs; rather, a straight line is drawn from the point of departure for the observed data (typically the BMDL) to the origin (where there is zero dose and zero response). The slope of this straight line, called the slope factor or cancer slope factor, is use to estimate risk at exposure levels that fall along the line. When linear dose-response is used to assess cancer risk, EPA calculates excess lifetime cancer risk (i.e., probability that an individual will contract cancer over a lifetime) resulting from exposure to a contaminant by considering the degree to which individuals were exposed, as compared to the slope factor. Thus,
Cancer Risk = Exposure x Slope Factor
Total cancer risk is calculated by adding the individual cancer risks for each pollutant in each pathway of concern (i.e., inhalation, ingestion, and dermal absorption), then summing the risk for all pathways.
Since the exposure level to the population is so low this is the only method they can use to compile those numbers. In other words no one is going to have died from a coal plant on their death certificate. Air pollution may be a contributing factor to their death but weighted against things like lifestyle it's a very small factor.
Last edited by thecoalman; 04-03-2013 at 05:29 PM..
That is not your extrapolation. Sorry you're mischaracterizing EPA's approach. The health problems associated with coal fire emission are not extrapolations but well within the range of the variables.
That is not your extrapolation. Sorry you're mischaracterizing EPA's approach. The health problems associated with coal fire emission are not extrapolations but well within the range of the variables.
My layman's example is exactly how a linear dose response assessment works, there is no other way to deal with the health effects of air pollution when you're trying to apply it to an entire population. If you have a better explanation lets hear it.
My layman's example is exactly how a linear dose response assessment works, there is no other way to deal with the health effects of air pollution when you're trying to apply it to an entire population. If you have a better explanation lets hear it.
Nope The EPA can and does sample from environments cleaner and more dirty than the US to understand the impact of air pollution on population health. They don't need to extrapolate outside the bounds of their independent variables.
Sorry I was confused, when you asserted the strawman argument I though it was an accusation. Your original intent of providing a great example is clear now.
The assertion is that the EPA extrapolates beyond the bounds of it's data. Strawman.
Reference one study from the EPA where they are making claims about the entire population that support what you are saying. Just one, pick anyone you want.
Perhaps I can pout this into a context easy for you to understand. We have child with asthma that lives in a house 2 miles from coal plant, the house is tighter than drum, the Mother uses harsh chemicals for cleaning but rarely cleans, there is 5 dogs in the house, the heat is ventless, the kid never goes out of the house and last but not least the house is filled with mold. What gave him the asthma?
Is it sinking in yet?
Last edited by thecoalman; 04-04-2013 at 06:52 PM..
Reference one study from the EPA where they are making claims about the entire population that support what you are saying. Just one, pick anyone you want.
You're the one claiming that their methods are unsound. Prove it.
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