Intertidal sediments from a range of depositional environments in the eastern Irish Sea have been analysed with regard to their radionuclide content, particle size distribution and magnetic properties. Concentrations of 241Am and 137Cs are highly influenced by the abundance of sediment finer than 32µm in fine-grained sedimentary environments, whilst radionuclide activity in coarser sediments is less dependent on particle size. Investigation of the magnetic properties of these sediments highlights a similar association between this size fraction and magnetic remanence, the latter being shown to offer strong potential as a grain size proxy in monitoring 137Cs concentrations in fine-grained sediments. Analysis of particle size fractions indicates the extent to which 137Cs may be enriched in the clay size fractions of both fine and coarse sediments.