The applicability of needle chemistry for diagnosing heavy metal toxicity to trees

To estimate the validity of needle chemistry as a tool for diagnosing heavy metal toxicity, we collected needle samples from mature pines and young seedlings and monitored metal deposition in the vicinity of a Cu-Ni smelter in SW Finland. Needle Cu, Ni, Zn and Fe concentrations in a pine stand growing next to the smelter were determined in 1992 and in 1998. Deposition was collected as bulk precipitation (open area) and as stand throughfall (below the canopy) during 1992-1998. Copper deposition in stand throughfall (TF) was relatively constant during 1992-1998, but for Ni in stand TF there was a strong increase from 100 mg m(-2) in 1997 to 600 mg m(-2) in 1998. There was a decreasing trend during the study period for both Zn and Fe deposition in TF, indicating a decrease in the emissions of these metals from the smelter. Washing the needles with chloroform removed a part of the Fe and Ni, but there was no clear difference for Cu or Zn between the washed and unwashed samples. However, needle Ni, Fe and Cu concentrations in pine seedlings grown in unpolluted soil close to the Cu-Ni smelter were considerably higher than in seedlings grown in a greenhouse in polluted soil taken from close to the smelter. Hence, our results suggest that not all the needle Ni, Fe and Cu derived from aerial deposition is washed-off from the canopy by rainfall (or by the washing of needle samples with e.g. chloroform).