[en] Using data for the discharge of effluents to the Irish Sea, from the nuclear fuel reprocessing plant at Windscale, the probable sedimentary deposition of ²⁴¹ Am and ²⁴¹Pu over the past 20 yr is estimated and the consequent additional ingrowth of ²⁴¹Am, due to decay of ²⁴¹Pu, is calculated. The latter is now approximately 600 Ci yr^-1, rising towards a steady state approximately 1,300 Ci yr^-1 if present rates of discharge of ²⁴¹Pu are maintained. The present sedimentary reservoir of ²⁴¹Am is approximately 18,000 Ci, of which about 4,800 have resulted from ²⁴¹Pu decay in situ. Measurements of the ²⁴¹Pu/Pu-α isotope ratio in coastal sediments confirms the estimates of ²⁴¹Pu deposition. Outside the Irish Sea, in the dispersal plume into Scottish waters, it is concluded that the observed ²⁴¹Am concentration can be accounted for largely by ingrowth from the ²⁴¹Pu transported in the water mass. (U.K.)