Radiometric investigation in a rainforest of the Golfo Dulce region of southern Costa Rica has shown the presence of the anthropogenic radionuclides caesium-137, strontium-90 and the plutonium isotopes 238, 239 and 240 along with the naturally occurring radionuclides 7Be, 40K, 238U and 232Th, and respective progenies. 137Cs, 90Sr and Pu can be attributed to global fallout; no other sources coul...