Scaling-Assisted Phytostabilization from the Greenhouse to the Field at the Iron King Mine-Humboldt Smelter Superfund Site
The Iron King Mine and Humboldt Smelter Superfund Site in Dewey-Humboldt, Arizona is an abandoned mine which tailings are prone to wind and water erosion, posing a possible health risk to neighboring communities and ecosystems. To help mitigate wind and water dispersion as well as the bioavailability of toxic metals in the tailings, we used a green remediation technology called phytostabilization. This technology is based on the establishment of a vegetative cap using native desert plants that do not accumulate toxicants in their leaves. Our objective was to evaluate whether field scale success can be achieved using desert native plants and compost rates from successful greenhouse phytostabilization trials. Tailings were amended with 10, 15, or 20% (w/w) of compost and were direct seeded with plants and an irrigation system. Parameters evaluated to indicate success included percentage of soil covered by plants, metal concentration in leaves, and the number of bacteria that can grow in neutral pH which correlates to healthy plants and soils.
At the site, compost amended planted plots successfully showed growth of plants mirroring results in the greenhouse. Seeded treatments achieved a canopy cover ranging 27% to 52%. No plants grew on unamended tailings. Metal accumulation in leaves was below Domestic Animal Toxicity Limits. The plots survived several heavy rain events during fall 2010 and monsoons while plant cover prevented erosion of the tailings. Evaluation of vegetation success and the correlated reduction in wind erosion will help to quantify the role of phytostabilization in decreasing the mobilization, transportation, dispersion, and deposition of hazardous contaminants into the surrounding environment. This study will be continued through 2015 to determine if tailings characteristics improve over time as a medium for plant growth and the long-term potential for plant survival in these tailings as a cost-effective green strategy.