Assessing the internalization pathways of Cr–Fe–Ni nanoparticles in native Dittrichia viscosa naturally exposed to industrial atmospheric fallout†

Native Dittrichia viscosa plant specimens growing near a steel factory were inspected for possible internalization of nanoparticles containing a mixture of chromium, iron, and nickel (Cr–Fe–Ni). There has not previously been evidence that nanoparticles of this composition generated during steel manufacturing processes can transfer to living organisms. This work seeks to also extend our understanding of the behavior of Dittrichia viscosa when exposed to the atmospheric fallout of particulate matter resulting from steel processing. It is unknown whether exposure to this fallout could influence uptake pathways in plants for Cr, Fe, and Ni containing nanoparticles. Dittrichia viscosa plant species were sampled from both a rural site and in proximity to an industrial region in Northern Tunisia that includes steel manufacturing activities. Different plant organs and the corresponding rhizospheres of Dittrichia viscosa were processed to isolate solid particulate matter. These isolated particles were analyzed using scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS) techniques. These solid fractions of isolated particles were also evaluated for their Cr, Fe, and Ni content by X-ray fluorescence (XRF) spectroscopy. These analyses demonstrated the presence of nanoparticles containing either Cr, Fe, or Ni in the rhizosphere and roots, but indicated that the stems and leaves of the plants grown near steel manufacturing sites contained predominantly Cr–Fe–Ni nanoparticles, containing a mixture of all three elements. Plant organs harvested from the rural site had an absence of Cr–Fe–Ni nanoparticles. The results also suggested that internalization of the Cr–Fe–Ni containing nanoparticles may have occurred upon foliar uptake as a major transport mechanism as these particles are predominantly present in the leaves and stems of the plants as a result of atmospheric fallout depositing onto the aerials surfaces of the plants. This study demonstrates a potential pathway for the inclusion of heavy metal containing nanoparticles into ecosystems and the food chain.