Phytoremediation of metal-contaminated bottom sediments by the common ice plant (Mesembryanthemum crystallinum L.) in Poland

Abstract

Abstract Purpose The aim of the study was to propose a phytoremediation-based approach toward the proper utilization of post-industrial, metal-contaminated bottom sediments. The common ice plant, Mesembryanthemum crystallinum L. (Aizoaceae), an abiotic-stress tolerant, C3/CAM intermediate halophyte, was tested for growth in substrates containing bottom sediments and for biological removal of metal pollutants. In variant tests, the sediments were admixed with non-toxic components to reduce the ecotoxicity hazards and improve growth conditions. Materials and methods Bottom sediment samples were collected from Lake Chechło in the industrial area of Poland. They were amended with universal soil and other materials (sand, lime, plant ash) and then used as growth substrates. After 30-day growth the plant biomass and rhizospheric microbiota population were assessed. The elemental content was determined in the substrate as well as in plant organs with inductively coupled plasma–optical emission spectrometry (ICP-OES). Bioaccumulation factors (BAFs, indicating phytoextraction processes) and root-to-shoot translocation factors (TFs) were calculated for all the metals to trace their behavior upon phytoremediation. Ecotoxicity assessments were performed by using a set of biotests (Phytotoxkit, Ostracodtoxkit F, and Microtox). Results M. crystallinum proved its ability to grow under harsh conditions of toxic and poor-quality substrates, while allowing for proliferation of rhizosphere bacteria. The plant growth was accompanied by the accumulation of Na and several other metals which were partially removed from the bottom sediment-containing soils. Depending on the experimental variant, the maximum removal achieved upon the 30-day test was: for Cd, 18.1%, Cu, 47.6%, Cr, 32.7%, Pb, 36.6%, and Zn, 24.1%. M. crystallinum hyperaccumulated Zn and accumulated (either in roots or shoots) Cd, Cu, Cr, and Ni. The maximum BAF values (> 1.0,) were obtained for the following metals: Cd, Cr, Ni, Cu (roots) and Cd, Cr, Ni, Zn (shoots). The highest values of TF (> 1), confirming high phytoremediation potential, were calculated for Na (33.33), Cd (1.47), Cu (1.77), Cr (7.85), and Zn (4.02). Bottom sediments revealed class III toxicity (acute), which was decreased by admixing with other materials. Surprisingly, the treatment with M. crystallinum led to an increase of toxicity levels, possibly by mobilizing potentially toxic elements during plant growth and microbial population development. However, mixing the sediments with universal soil and lime enabled us to maintain class I (no acute toxicity). Conclusion The common ice plant reveals strong application potential for use in reclamation of soils or revitalization of industrially degraded areas containing bottom sediments.