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Answer:
When the ERICA database was derived those responsible for deriving the freshwater CR values assumed (pressumably because of a lack of available data at that time) that the the Pb concentration ratio (which estimates the activity concentration in fish simply from that in water) were was the same for benthic and pelagic fish. Therefore, the estiamted estimated whole-organism Pb-210 activity concentration concentrations in the benthic and pelagic fish will be identical. The internal dose rate rates will be similar for the two fish as difference the differences in their geometry does do not result in large variation in DCC values.

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_If you assume that an organism is at the sediment water interface the external does rate is estimated as:
0.5*(DCCexternal*sediment activity concentration) + 0.5*(DCCexternal*water activity concentration); sediment will generally contribute the most to the total external dose rate. If you do not have sediment activity concentrations to input these will be estimated from kd and input water activity concentrations._

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