THE ABIOTIC STRESS RESPONSE OF HYDROPONIC VETIVER GRASS (Chrysopogon zizanioides L.) TO ACID MINE DRAINAGE AND ITS POTENTIAL FOR ENVIRONMENTAL REMEDIATION

Mining activities can generate acid mine drainage (AMD), an acidic discharge that contains elevated sulfate (SO42-), soluble metals, and orange-yellow metal-containing particulates. AMD imposes ecological risks from metal toxicity and physical stress, which may physically spread to nearby water sources or biologically through bioaccumulation. Current methods for AMD treatment, such as chemical or passive biological treatments, are often non-sustainable. Chemical treatments can be expensive and create large amounts of secondary waste, whereas biological treatments like anaerobic wetlands require continuous maintenance through input of organic nutrients. The end goal of this research is to develop a cost-efficient and sustainable floating treatment wetland (FTW) system to remediate AMD-impacted waters from the abandoned Tab-Simco mining site in Southern Illinois. AMD from the site is acidic, having a pH of 2 to 3, with elevated amounts of SO42-, Fe, Al, Mn, Zn and lower amounts of various other metals. Vetiver grass (Chrysopogon zizanioides) is a non-invasive and fast-growing plant that can grow sustainably under hydroponic conditions. Moreover, vetiver is tolerant of acidic conditions and metals, and is a known hyperaccumulator of Pb and Zn. A short-term (30-day), bench-scale experiment revealed that vetiver was tolerant of Tab-Simco AMD and able to improve water quality by increasing pH and reducing the amounts of SO42- and soluble metals. In a follow-up, year-long mesocosm experiment, vetiver plants were positioned on rafts for FTWs and suspended in 378.5-liter containers filled with 170 liters of unfiltered Tab-Simco AMD while additional plants were suspended in AMD that was passed through a plug-filter with recycled materials designed to remove metals and neutralize the water. From the unfiltered AMD, there was high net removal of SO42- (28%), Fe (81%) and Pb (81%) with lower removal of Ni (38%), Zn (35%), Mn (27%), Cr (21%), Al (11%) and Cu (8.0%). From the filtered AMD, there was little to no remaining metals, though there was high net removal of SO42- (45%). Vetiver accumulated Fe \u3e Al \u3e Mn \u3e Zn \u3e Cr \u3e Ni \u3e Cu \u3e Pb. The majority of metals were localized on the root surface as Fe plaques, though Mn and Zn demonstrated greater translocation to the shoots. Moreover, vetiver biomass was deemed non-hazard following metal accumulations through TCLP. An additional year-long microcosm experiment was conducted to ensure complete root coverage by vetiver, which resulted in superior remediation with near complete removal of SO42- (91%) and most metals (90-100%) with the exception of Pb (15%) and Cu (0.0%). These remediation experiments demonstrate that vetiver can effectively improve AMD-impacted waters; however, little was known about tolerance mechanisms. Therefore, metabolomic analysis of vetiver was conducted over relatively short-term (7-days) and long-term (56-days) periods of exposure to Tab-Simco AMD. After long-term exposure, vetiver shoots showed dramatic upregulation of amino acid (AA) and glutathione metabolism, along with respiration and photosynthesis pathways, and downregulation of phosphorylated metabolites. There was drastic downregulation of phosphorylated metabolites in the roots, particularly with phospholipids, as well as respiration, glyoxylate and AA metabolism. It was suggested that oxidative stress, resource deprivation (nitrogen and phosphorus), and dehydration were among the main forms of abiotic stress