Study of seasonal variations of trace-element concentrations within tree rings by thick-target PIXE analyses

Thick-target PIXE has been used for the quantitative determination of trace elements in annual growth rings of different tree species. A scanning device was developed for the remote control of the sample and a video-camera system for the exact monitoring of the spot to be analyzed. The samples were analyzed in steps of 1 mm. The widths of the tree rings studied were in the range 2.5-8.0 mm. Samples of Norway spruce and Scots pine were collected from Harjavalta, a polluted area in southwestern Finland. The elements studied were S, Cl, Br, K, Ca, Mn, Fe, Zn, Cu, Ni, Pb, Rb and Sr. Large variations were observed in elemental concentrations within individual tree rings. The highest concentrations for most elements were obtained for earlywood in the beginning of the growth season and the lowest values for latewood thus reflecting the biological activity. The method was calibrated using international standard reference materials. For most elements the matrix effects were found to be negligible. The detection limits for most metals studied were in the range 1-5 ppm.