The given definitions of isotopes of plutonium 238, 239+240, cesium-137 and potassium-40 in a column of bottom sediment of sea territory of delta of the Northern Dvina cited in the research work. The territory near Severodvinsk has been tested. Isotope correlation of isotopes of plutonium and caesium-137 specify an origin anthropogenic radionuclide in the delta from two sources - nuclear explosions in the atmosphere and on surfaces of the ground in world experience and Chernobyl explosions.