AZ Phytotoxicity and Phytoremediation Potential of Mercury in Indian Mustard and Two Ferns with Mercury Contaminated Water and Oak Ridge Soil - 9241

Phytoremediation is an emerging technology that uses various plants to degrade, extract, contain, or immobilize contaminants from soil and water. Certain fern and Indian mustard species have been suggested as candidates for phytoremediation of heavy metal-contaminated soil and water because of their high efficiency of accumulating metals in shoots and their high biomass production. Currently, no known hyperaccumulator plants for mercury have been found. Here we report the Hg uptake and phytotoxicity by two varieties of fern and Indian mustard. Their potential for Hg phytoremediation application was also investigated. Anatomical, histochemical and biochemical approaches were used to study mercury phytotoxicity as well as antioxidative responses in ferns [Chinese brake fern (P. vittata) and Boston fern (N. exaltata)] and Indian mustard (Florida broadleaf and longstanding) (Brassica juncea L.) grown in a hydroponic system. Phytoremediation potentials of these plant species were estimated based on their Hg uptake performance with contaminated soils from Oak Ridge (TN, USA). Our results show that mercury exposure led to severe phytotoxicity accompanied by lipid peroxidation and rapid accumulation of hydrogen peroxide (H2O2) in P. vittata, but not in N. exaltata. The two cultivars of fern responded differently to mercury exposure in terms of antioxidative enzymes (superoxide dimutase, SOD; catalase, CAT; peroxidase, POD; glutathione redutase, GR). Mercury exposure resulted in the accumulation of ascorbic acid (ASA) and glutathione (GSH) in the shoots of both cultivars of fern. On the other hand, Indian mustard effectively generated an enzymatic antioxidant defense system (especially CAT) to scavenge H2O2, resulting in lower H2O2 in shoots with higher mercury concentrations. These two cultivars of Indian mustard demonstrated an efficient metabolic defense and adaptation system to mercury-induced oxidative stress. In both varieties of fern and Indian mustard, a majority of Hg was accumulated in the roots and low translocations of Hg from roots to shoots were found in two cultivars of Indian mustard. Experiments with aged soil indicate that fern can accumulate up to 1700-2000 mg/kg Hg in roots and 60-170 mg/kg in shoots, while two varieties of Indian mustard accumulated up to 2000-4000 mg/kg Hg in roots and 260-430 mg/kg Hg in shoots from contaminated Oak Ridge soil. Thus, these varieties of Indian mustard and N. exaltata (fern) might be potential candidate plants for phytoremediation of mercury-contaminated water and soils. More field studies are planned for further evaluation.