Chapter 5: Application of radiocaesium microscale observation methodology to parmelioid lichen and ultrastructural analyses using STEM-EDS

A method to examine the localisation of radiocaesium in lichen thallus tissues using autoradiography was applied to the parmelioid lichen, Punctelia borreri, collected six years after the Fukushima Dai-ichi nuclear power plant accident. Radiocaesium was detected in the lower cortex of thallus tissues and associated rhizines that contained brown melanin-like pigment. This finding was consistent with our previous findings for the lichen Parmotrema tinctorum. In addition, we observed the ultrastructure of upper cortex tissue within Parmotrema tinctorum using STEM-EDS analysis, where a sub-micron particle was found to be present inside the tissue. The presence of radiocaesium particles in the cortex matrix of the lichen, similar to other sub-micron particles, may be a factor in the long-term retention capability of radionuclides within lichens.