[en] The fallout radioisotope ^113mCd (t_1/2 = 14.6y, 99% β^-, E_max 0.59 Mev) has been determined in sediment and soil cores from the Sapelo Island National Estuarine Research Reserve. In soils, the isotope occurs in the upper few inches, where ¹³⁷Cs is also found. In recent marsh sediments (²¹⁰Pb geochronology), ^113mCd exhibits a more complex pattern, including subsurface maxima at some locations. The total ^113mCd burden in sediment cores indicates that Cd deposited in the estuary from the atmosphere is retained to a significant extent in accumulating sediments