SEASONAL VARIATIONS OF HEAVY METAL CONTENTS IN THE NEEDLES OF SOME EVERGREEN TREES IN GREEN SPACES OF YEREVAN (ARMENIA)

The main aim of this research was to study a metal accumulation potential of two evergreen species Thuja occidentalis L. and Juniperus virginiana in different periods of plant vegetation in Yerevan. The total contents of 6 microelements: Pb, Cd, Ni, Zn, Cu, Mo in plant material were determined by atomic absorption spectrometry (A Analyst 800, Perkin Elmer, USA). The research results have proved that metal concentrations in the needles of evergreen trees are variable depending on a vegetation period and disposition relative to roads with heavy traffic and industrial pollution sources. The concentrations of the studied elements in the needles did not exceed the standard values both in summer and winter, except Mo, which was high in both species nearby industrial pollution sources. The total average contents of metals in the needles increase in winter.