Cd enrichment and distribution in broad bean seedlings under stress of Cd combined with MWCNTs-COOH

Nanomaterials are inevitably released into the environment because of developed production and application, which brings potential risks to the ecological environment and human health. The aim of this study was to explore the effect of MWCNTs-COOH and heavy metals Cd double stress on Cd enrichment, transport, and distribution in plant organs, and provide a theoretical basis for evaluating phytotoxicity and ecological risk of the combined pollution of MWCNTs-COOH and Cd. In this study, broad bean seedlings were cultured as experimental material using the hydroponics method, and MWCNTs-COOH (0 mg·L^-1, 1.5 mg·L^-1, 3.0 mg·L^-1, 6.0 mg·L^-1, 12.0 mg·L^-1) and 10.0 μmol·L^-1 Cd treatment groups were set. The contents of Cd in roots, stems, leaves, and cells of broad bean seedlings under the different treatments were determined by Graphite Furnace atomic absorption spectrometry; and Cd enrichment, transport in vegetative organs, and distribution in cells of broad bean were analyzed. The results showed that Cd contents in three kinds of vegetative organs under MWCNTs-COOH and Cd compound stresses were higher than those in CK. Cd enrichment in roots, stems, and leaves; Cd enrichment coefficient, and translocation coefficient between organs (root-stem and stem-leaf) all first increased and then decreased. The above indicators reached their maximum values when the concentration of MWCNTs-COOH was 6.0 mg·L^-1. At the same time, with the increase of MWCNTs-COOH concentration, Cd in cells of roots, stems, and leaves gradually transferred from cell wall to protoplast, which deepened the toxicity to cells. In conclusion, medium and low concentrations of MWCNTs-COOH not only promoted Cd accumulation and upward transport in roots, stems, and leaves, but also enhanced Cd transfer in cells.