Dendrochemical analysis of heavy metals in Magnolia champaca tree rings in Mizoram, Northeast India

Abstract

Heavy metals are among the important environmental pollutants, yet their impact in remote areas remains underexplored because of limited studies on their monitoring. This study presents the first dendrochemical analysis from Mizoram, using Magnolia champaca tree rings to assess heavy metal concentration trends at a natural forest site (Site-I) and a roadside plantation (Site-II) for about two and half decades (from 1993 to 2019). The concentrations of Zn, Pb, Fe, Cu, Ni, and Mn were analyzed in tree rings to reconstruct pollution history. The results revealed a significant difference between the two sites, with roadside tree cores exhibiting greater variability and steadily increasing heavy metal concentrations as compared to natural forest. The mean concentrations of metals in natural forest samples were in the order: Fe (18.22 mg kg⁻¹) > Mn (12.01 mg kg⁻¹) > Ni (7.23 mg kg⁻¹) > Cu (3.71 mg kg⁻¹) > Pb (0.398 mg kg⁻¹) > Zn (0.411 mg kg⁻¹). In contrast, roadside samples showed considerably higher metal concentrations in the order: Mn (39.92 mg kg⁻¹) > Fe (22.9 mg kg⁻¹) > Ni (11.61 mg kg⁻¹) > Cu (10.28 mg kg⁻¹) > Zn (6.723 mg kg⁻¹) > Pb (3.17 mg kg⁻¹). Notably, M. champaca samples collected from the roadside contained elevated levels of Pb, Fe, Cu, and Ni, exceeding the permissible limits for plant parts as prescribed by the WHO. The study underscores the potential of species as a bioindicator of heavy metal pollution. These findings are crucial for informing soil management, pollution control, and understanding nutrient-metal cycling in trees. Further research is needed to explore the plant-soil interactions and behaviours of heavy metals in these environments.