Three nuclear analysis techniques, the proton microprobe (mu-PIXE), instrumental neutron activation analysis (INAA), and alpha-track autoradiography were used to determine the temporal history of concentrations of elements in shells of the freshwater pearl mussel, <i>Margaritifera margaritifera</i> from 4 rivers in central Sweden. The high spatial resolution (3 mum) of mu-PIXE allows analyses of samples representing small parts of single years. Thirty elements were identified and quantified using INAA technique. Elemental concentrations in old samples (from 1860) were similar to those from young specimens (1970-1985). Silver, gold, iron, and cobalt decrease strongly, and manganese and sulfur increase in connection with acidification after 1940. The present study indicates that shells of living mussels, together with museum or subfossil shell material, may be used to date environmental changes caused by natural events, and large-scale industrial, agricultural, or nuclear contamination. -- AATA