Variations of trace element concentrations in red spruce tree rings

The potential of coniferous trees as biological indicators of heavy metal atmospheric pollution was investigated. In 31 municipalities of an industrialized region, samples of wood from the trunks of red spruce (Picea rubens ) were taken to determine the spatial distribution of accumulated metals. The concentrations of Mg, Al, Ca, Mn, Fe, Cu, and Zn were measured by neutron activation analysis. All metals showed the highest concentrations in the most recent wood and the bark. For the wood older than 5 yr, Mn and Zn are stable with time, Mg and Ca decrease, while Al, Fe, and Cu appear to increase. As expected, trees in towns near metal refineries contain higher amounts of Mn, Fe, and Al. Large variations in metal concentrations, due to factors not totally understood, were observed. Thus, red spruce is not a sensitive bio-indicator of atmospheric metal pollution.