4.3. Surface Deposition Affected Cu and Ni Concentrations
The Cu and Ni concentrations in the compartments subjected directly to aerial deposition (bark, young shoots, and foliage) were clearly higher than those of wood and roots.
A high proportion of these metal concentrations is caused by aerial deposition of dust that accumulates on the plant surfaces and do not penetrate into the living tissues [18,35,36].
Thus, high amounts of heavy metals on plant surfaces do not necessarily pose any acute toxic hazard to plant metabolism.
Tree bark is known to sorb and accumulate airborne contaminants and therefore, it has been largely used for monitoring of atmospheric pollution [37-39].
In our study the whole bark layer, including the living inner bark, was taken by peeling it completely from the tree shoots.
The inner bark metal concentrations reflect the phloem sap flow.
The Cu and Ni concentrations in the bark obtained in our study are roughly hundreds of times higher than the nationwide mean values (3.6 and 1.1 mg·kg−1, respectively) reported by Lippo et al. [35].
Also Saarela . [39] found lower metal concentrations (Cu 89 mg·kg−1 and Ni 18 mg·kg−1) than our values in Scots pine bark sampled during forest felling 6 kilometers northeast from the Harjavalta smelters.
Scots pine needle Cu concentrations ranging from 1.7 to 270 mg·kg−1 and Ni g·kg−1 have been found in a 350 km-long transect extending from the Monchegorsk smelter complex, NW Russia, through Finnish Lapland to the Finnish-Swedish border [40-43].
We found even higher concentrations, Cu ranging from 100 - 600 mg·kg−1 and Ni from 50 - 140 mg·kg−1 in our study than the values reported from the Kola gradient.