Proof of concept to characterize historical heavy-metal concentrations in atmosphere in North Turkey: determining the variations of Ni, Co, and Mn concentrations in 180-year-old Corylus colurna L. (Turkish hazelnut) annual rings

Heavy metals (HMs) are among the pollutants posing a significant threat to human, animal, and environmental health. Therefore, monitoring HM concentration changes, especially in the air, is crucial. This study used Corylus colurna L. (Turkish hazelnut) annual tree rings cut in 2020, and it was intended to define the 180-year variations in concentrations of Ni (nickel), Co (cobalt), and Mn (manganese) that are among the most harmful HMs. This study analyzed HMs concentrations in the wood, outer and inner bark in the north, south, east, and west directions and the seasonal variations in HM concentrations in tree rings. It was determined that, for all the three elements, the wood and barks significantly differed (P < 0.001) only in the north side, and the concentrations in wood were much lower than in the bark. The maximum concentrations were usually observed in annual rings in the west and south directions. The changes by both organ and direction can be related to the iron and steel factory and the highway, which are defined as HM sources. The results also revealed that the relocation of Co, Ni, and Mn in the wood of C. colurna tree remained at a limited level. The results suggest that C. colurna annual tree rings are very useful in tracking the variation of Ni, Co, and Mn concentrations.