Investigation on Pollution Status of Poplar Trees (Populous nigra) around the Zanjan's Lead and Zinc Factory using Annual Growth Ring

One of the newest methods to determine the amount and type of many environmental pollutants is the use of natural bio-detector method. In the temperate regions a layer of wood (growth ring) is yearly added to the tree, in which the growth ring, habitat conditions recorded in the same year are a good option for bio- detector over time. In this research, the poplar trees which are abundantly cultivated around the Zanjan's lead and zinc factory were used as a bio-detector to illustrate the process of surrounding soil pollution. For this purpose, 2 trees were selected and cut from 5 and 10 km intervals of Zanjan's lead and zinc factory as well as was sampled from the surrounding soil of each tree. The age of the trees was determined through the annual rings (growth rings). The concentration of lead and zinc was determined in each of the annual ring and also soil samples. The results demonstrated that the amount pollution of soil and wood samples near to the mentioned factory was higher than other samples. The amount of lead and zinc in the annual growth rings of poplar tree showed an increasing trend from 1991 to 2010, but this increase was significantly observed in the trees close to the factory. The statistical analysis demonstrated a significant correlation between the amount of lead and zinc with the aforementioned years (p˂0.01). The amount of lead and zinc in the studied soils and trees were also increased per year. Furthermore, the statistical analysis (correlation analysis) indicated that there is no significant pollutants movement between the annual rings. Therefore, it can be concluded that poplar trees can be used as a bio-detector for the polluted soils to lead and zinc metals in the study area.