SORPTION OF RADON-222 TO NATURAL SEDIMENTS

Abstract The sorption of Rn to sediments was investigated, since this may affect the use of porewater Rn profiles for estimating bed irrigation rates. Batch experiments showed that Rn has an organic carbon normalized sediment-water partition coefficient (Koc) of 21.1 ± 2.8 for a Boston Harbor sediment, 25.3 ± 2.1 for a Charles River sediment, and 22.4 ± 2.0 for a Buzzards Bay sediment. These values are in close agreement with predictions using the octanol-water partition coefficient (Kow) which we measured to be 32.4 ± 1.5. Temperature and ionic strength effects on Koc were estimated to be small. Given rapid sorption kinetics, we suggest that slurry stripping techniques used by many investigators to measure 222Rn in sediment samples collect both sorbed and dissolved radon. Sorption effects were included in a transport model to obtain revised estimates of irrigation rates from existing literature profiles. Irrigation rates had to be increased over previously reported values in proportion to the sediment organic matter content.

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