UTILIZATION OF COPPER CONTAMINATED MARGINAL LAND: VETIVER PERFORMS PHYTOSTABILIZATION AND CAN BE HARVESTED AS A SECOND-GENERATION BIOETHANOL FEEDSTOCK

Historical copper mining practices in the Keweenaw Peninsula of Upper Michigan have created over 500 million tons of mine waste rich in copper, called stamp sands. The stamp tailings were disposed of into various rivers, waterways, Lake Superior shorelines and the Keweenaw Bay. The acreage where the mine waste was dumped is now considered marginal due to the lack of vegetation cover, which makes it prone to erosion into the surrounding surface water, threatening the aquatic ecosystem. Vetiver grass (Chrysopogon zizanioides L. Nash) is a lignocellulosic hyperaccumulator of many xenobiotics and was evaluated for its phytoremediation capacity in copper loaded stamp sand, at concentrations of 1551 ± 28 ppm. A 60-day study was performed in a greenhouse setting to measure the phytotoxicity of copper exposure on vetiver, the uptake and stabilization of copper and erosion control by vetiver, and the effects of copper contaminated soil on the lignocellulosic composition of vetiver for impact on downstream fermentation. Chlorophyll content in vetiver shoot was not affected by the presence of high copper, while biomass, shoot length, and root length were significantly impacted. The bioconcentration factor for copper uptake by the roots was significantly greater than that of the shoots, resulting in phytostabilization of copper within the rhizosphere. The lignin content decreased, and hemicellulose and cellulose content increased significantly in the copper treated group over the course of the study, when compared to control plants grown in uncontaminated soil. The study demonstrates the feasibility of vetiver grass cultivation on metal-contaminated marginal land, and using the aerial biomass as a bioethanol feedstock.