EPITHERMAL NEUTRON ACTIVATION ANALYSIS OF MOSSES USED TO MONITOR HEAVY METAL DEPOSITION AROUND AN IRON SMELTER COMPLEX

摘要

The moss Hylocomium splendens was used as a biomonitor to study changes in the atmospheric deposition of metals around an iron smelter complex in Northern Norway between 1989 and 1993. Samples representing the last three years' growth of moss, collected on the ground at 25 sites located 1-25 km from the source area, were analysed by instrumental neutron activation analysis using epithermal neutrons. A total of 38 elements were determined, including most of the heavy metals known to be released into the air from this kind of industry. A re-orientation of the industrial production occurred around 1990; the most important developments being the closing of an iron smelter and the starting-up of a new ferrochrome smelter, Accordingly, the Cr deposition in the vicinity of the smelter increased by about a factor of 100, while the Fe deposition decreased by almost a factor of 10. Other elements showing a decrease over this period were Mo, Sr, Se, Zr, Re, Hf, Ta, Th, and Il, while there was an appreciable increase for Ni, W, and Au. Most other elements, including V, Mn, Co, Cu, Zn, As and Sb, had similar levels as before. A new method for the graphical representation of deposition levels is introduced. Instead of constructing isopleths based on the observed concentration values, each value is divided by a number representing the background level found in moss in the area. The resulting ratios are then used as a basis for the construction of isopleths. Examples are shown for Cr, Fe and V levels in 1989 and 1993 respectively. [References: 16]