Concentration of Heavy Metals in Bark Samples of Pine Trees in Neishabur, Iran

Heavy metals in urban air are major health threats and increase the risk of respiratory, cardiovascular, and cancers in humans. An efficient and low-cost method for monitoring these pollutants is using tree bark as a bioindicator. The purpose of this study was to measure the concentration of heavy metals by pine tree bark as a bioindicator in Neishabur, north-east of Iran and the ecological risk of these pollutants.

Twenty seven locations were determined on Neishabour map using GIS. Concentrations of heavy metals, including silver (Ag), arsenic (As), cobalt (Co), cesium (Cs), manganese (Mn), lead (Pb), copper (Cu), zinc (Zn), chromium (Cr), and cadmium (Cd) were measured using Inductivity Coupled Plasma-Mass Spectrometry. Ecological risk potential index, total ecological risk, and Spearman correlation coefficient were examined.

In this study, Cr and Zn had the highest average concentrations (34.7 mg/kg and 10.2 mg/kg,respectively) and other heavy metals in the bark were in the following order: Mn>Cu>Co>Pb>As>Ag>Cd>Cs. The average ecological risk potential decreases as Cd>As>Pb>Zn>Cu>Cr. Ecological risk potential index for all heavy metals except As and Cd (medium risk) was found to be at low-risk levels. The total ecological risk index showed that the concentrations of the studied heavy metals are at low-risk levels. Spearman correlation analysis showed that Cs and As had the highest correlation among the elements and there is a considerable relationship between these heavy metals which indicates the same source of pollution. Cr and Cd also have a strong correlation and have the same source of contamination.

The present study showed low risk of heavy metal pollution according to the average ecological risk potential in pine bark samples in Neishabour.