03-23-1992 Council Packet - Laserfiche WebLink

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-V -:;- .-; 'Mf- te-'- •tA. ■ li-i } •■ ■ i-rV'. v'* ^3'v.. l7- 'Wf. . I •* ■ :> j'fev i'4. k. Y.-;r- 92-47.03 animals, and fish within a given distance from the source over a specified period of time. This contaminant modeling tool is a predictive means of estimating the uptake, bioconcentration, and biomagnification of airborne pollutants through several ecological trophic levels and exposure routes. Ultimately, total human uptake (^g/day) of contaminants is estimated along with the relative contributions of the various exposure routes examined. Figure 2 illustrates the trophic exposure pathways. Three routes of vegetative uptake are considered; Uptake by the plant root system Wet and dry foliar deposition Contaminant vapor phase uptake by the aerial portion of plant This model estimates uptake for animal fe d grain and forage vegetation as well as crops consumed by man. It predicts contaminant concentrations in animal tissue resulting from inhalation and ingestion exposures. Ingestion of animal tissues and crops are both included in the total human exposure. Calculation of aquatic deposition permits evaluation of contaminant uptake by fish and, subsequently, human exposure via ingest:on of contaminated fish flesh. Risk Characterisation The risks to human health are characterized quantitatively. Quantitative risk estimates are generated through the use of Carcinogenic Slope Factors and Reference Doses. The ratio of Dose to Reference Dose is termed a Hazard Quotient and is a measure of the potential health effects of a given exposure. Thus: Hazard Quotient = Dose Reference Dose The hazard quotient is, therefore, simply a comparison between the amount of a chemical to which a person is exposed and an acceptable amoufit (RfD) published by the U.S. ERA. The U.S. EPA (U.S. EPA 1989) explains that a reference dose (RfD) is an "estimate (with uncertainty spanning perhaps an order of magnitude or greater) of a daily exposure level for the human