Selenium bioaccumulation in industrialized urban forests: case study of five tree species used for phytoremediation

Heavy metal pollution poses significant risks to ecosystems and human health, necessitating effective monitoring and mitigation strategies. This study focused on the priority pollutant selenium (Se) content, evaluating five tree species (Tilia tomentosa, Robinia pseudoacacia, Cedrus atlantica, Pseudotsuga menziesii, and Fraxinus excelsior) to assess their capacity to biomonitor and mitigate Se in urban parks of Düzce (Türkiye). We quantified Se accumulation in the outer bark, inner bark, and wood across the four cardinal directions of the stem. Results showed striking inter-species variation: R. pseudoacacia and C. atlantica woods accumulated exceptionally high Se concentrations (91.9 and 77.4 mg·kg⁻¹, respectively), while P. menziesii and F. excelsior showed non-detectable levels. Strong directional effects were pronounced, e.g., with the north aspect in C. atlantica accumulating 2.7× higher Se than the east aspect (77.40 vs. 28.09 mg·kg⁻¹). Se was generally higher in bark than wood. C. atlantica is recommended for phytoremediation due to constrained inter-tissue translocation (e.g., north-south differential: 45.39 vs. 36.10 mg·kg⁻¹). In comparison, R. pseudoacacia showed high bioavailability but high variability by cardinal direction (66.40–91.92 mg·kg⁻¹). These findings reveal species-specific Se accumulation patterns influenced by microenvironmental factors, emphasizing the targeted use of R. pseudoacacia and C. atlantica for pollution monitoring and Se mitigation in urban areas.