Extrapolation across exposure durations

These three commonly encountered problems in dealing with the dose-response step of the risk assessment process (and there are others as well) are respectively referred to as the problems of (1) high-to-low dose extrapolation (2) extrapolation across exposure durations ... 

Describe the route, level, stage, and duration of exposure as compared with expected human exposures, including available toxicokinetic data used to extrapolate across routes of exposure. 

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