Norway spruce (Picea abies) needles as potential indicator for heavy metal air pollution in Sarajevo

During winter, Sarajevo has one of the highest air contaminations in the world through its geographical situation (basin that is surrounded by mountains), coal combustion, and high traffic. As Norway spruce (Picea abies L.) is widespread in Sarajevo, we aimed to use this evergreen tree to provide a first biomonitoring assessment of the heavy metal pollution in Sarajevo. Needle samples of Norway spruce were collected from 13 different locations in Sarajevo with high traffic pressure in winter 2024. Four sampling sites located far away from traffic were used as rural control sites. From all the trees, 1-3-year-old needles were sampled. Samples were milled, microwave digested, and heavy metal concentrations were measured using atomic absorption spectroscopy with flame atomization (FAAS). The average concentrations of the heavy metals in urban areas followed the sequence Cd < Cu < Pb < Zn < Mn < Fe, while this sequence differed in the controls: Cd < Ni < Cu < Pb < Fe < Zn < Mn. The Pb, Ni, and Fe concentrations were significantly higher in the urban area compared to the controls while Mn was higher in controls. Multivariate PCA analyses suggest that Fe is mostly derived from anthropogenic sources while Mn derived from geogenic sources. The Pb, Fe, Zn, Ni, and Cu concentrations increased on needles with increasing age due to an accumulation of metals over 3 years. These results suggest that Picea abies has potential as a bioindicator for environmental monitoring of zinc, iron, and lead accumulation, where lead mostly originates from atmospheric deposition. However, further studies are warranted to confirm its reliability and suitability for long-term monitoring applications.