I. Phytostabilization of Mine Tailings in Arid and Semi-Arid Environments:

    Plant-Soil-Microbe Interactions and Metal Speciation Dynamics 

Motivation: Mine tailings are a significant health risk to nearby populations and they require novel remediation approaches that are economical and low input. In arid regions, mine tailings and their associated contaminants are prone to wind-borne (eolian) dispersion and water erosion.These problems are extensive and persistent because impacted sites are devoid of vegetation and lack the characteristics that result in normal soil stabilization.



Phytostabilization: Phytostabilization is a remediation technology that results in the vegetation of mine tailings with sufficient coverage to reduce wind and water erosion. It seeks to accumulate metals in the root zone, rather than to extract them into above-ground biomass, so as to prevent metals from entering the food chain.

Soil Microbes: Our research is showing that the role of soil microbes in plant establishment is particularly important because the tailings environment is characterized by severe stressors that include low pH, high metal content, high salinity, lack of soil structure, lack of mineral nutrients and organic matter, and poor microbial diversity. As a result of these stressors, normal plant-microbe interactions are inhibited completely or are slow to develop. Successful revegetation results in extensive plant root-microbe activities and interactions that promote the development of beneficial soil characteristics in the tailings.

Research Goal: The overall goal of our research is to determine how plant-microbe-metal interactions affect the short- and long-term requirements for, and mechanisms of revegetation of mine tailings and to identify the biological and physico-chemical markers that indicate successful remediation. 

A mine tailings site in northern Mexico showing erosion of the tailings on a windy day.  (Courtesy of Blenda Machado)  

(Above) Water erosion trench at the Klondyke Arizona State Superfund site.  This site is adjacent to Aravaipa Creek, an important riparian corridor in southern Arizona.  Many older mine sites such as this were located adjacent to creeks and streams which were used as water sources for milling operations. It is typical to find that the tailings piles at these sites have been physically eroded during periods of high water.  The particular erosion trench shown in this figure was formed during severe flooding that occurred during the 2006 summer monsoon.  Aravaipa Creek, which is ephemeral in this area, can be seen in the background. (Courtesy of Christopher Grandlic)


Plant Growth in Mine Tailings:  We have worked with a variety of mine tailings that range from neutral pH and low metal content to low pH and high metal content.  The challenge for all of these tailings types is that soil structure is absent, nutrient levels are extremely low, and the heterotrophic microbial community is extremely stressed.  We have found that a minimum of 10% (w/w) addition of compost to these tailings can allow for plant establishment by immediately addressing some of these challenges (improving tailings structure, adding nutrients and a heterotrophic inoculum). 

Tailings with low pH and high metals may require even higher levels of compost.  For example a greenhouse experiment was performed to determine the minimum compost necessary to establish plants in tailings from the Iron King Mine Superfund site (Dewey-Humboldt, Arizona).  These tailings have pH ranging from 2.5 to 3.5 and arsenic and lead concentrations ranging up to 4000 mg/kg.  A native grass, Buchloe dactyloides (Buffalo grass), was grown for 58 days in the tailings at 0, 10, 15, and 20% compost.  As the photos show, a minimum of 15% compost was required for optimal growth of this grass.  (Photo, courtesy Fernando Solis Dominguez, 2009)


Metal Speciation in Mine Tailings:  We are coupling molecular-biological and synchrotron-based-spectroscopy tools to examine metal speciation before and after revegetation of mine tailings.  The premise of this work is that alteration of mine tailings biogeochemistry - by inducing an active C cycle through revegetation- can lead to significant changes (we hypothesize reductions) in metal bioavailability. 

One example from this work shows the use of fluorescent in situ hybridization (FISH) to examine root colonization by bacteria. The accompanying FISH photos show  Buchloe dactyloides root tips from plants grown in mine tailings from Klondyke Arizona with different amounts of compost amendment.  The FISH probe used was a universal probe EUB338 labeled with the CY5 fluorophore.  Arrows point to bacterial colonies.  The photo on the left shows very minimal colonization of a root grown in mine tailings with no added compost.  The photo in the middle shows heavier bacterial colonization on a root tip grown in mine tailings amended with 15% (w/w) compost. A second experiment used FISH to quantify the % root colonization (as represented by % root fluorescence) in plants grown in 0, 5, and 10% compost-amended Klondyke tailings.  As shown in the Figure on the right, the amount of colonization on roots significantly increased as the compost amendment increased from 0 to 10%.


A second example from this work shows how we have been able to image the same root using FISH, scanning electron microscopy (SEM), and synchrotron-based-spectroscopy tools including microfocused X-ray fluorescence spectroscopy (u-XRF),  X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) spectroscopy.

(Above) Three micrographs of same root acquired using (a) FISH with a universal probe, (b) µ-XRF (tricolored map of Pb-S-Fe, pixel resolution 2-3 µm), and (c) SEM showing root associated particles and bacteria (inset). (d) µ-XANES and (e) µ-EXAFS of a root tip region enriched in Pb (circled in white), 2-3 µm on a side.  According to FISH, Pb-enriched particle is associated with high microbial activity in glycocalyx region. 




Phytostabilization Relevant Publications:

Hayes, S.M., S.M. Webb, J.R. Bargar, P.A. O'Day, R.M. Maier, J. Chorover, 2012. Chages Geochemical weathering increases lead bioaccessibility in semi-arid mine tailings. Environ. Sci. Technol., in press.

Solís-Dominguez, F., S.A. White, T. Borrillo Hutter, M.K. Amistadi, R.A. Root, J. Chorover and R.M. Maier. 2012. Response of key soil parameters during phytostabilization in extremely acidic tailings: effect of plant species, Environ. Sci. Technol. 46:1019-27. PMC32638

Hayes, S.M., P.A. O’Day, S.M. Webb, R.M.

Maier, and J. Chorover.  2011.  Changes in zinc speciation with mine tailings acification in a semiarid weathering environment.  Environ. Sci. Technol., 45:7166-7162.

Solis-Dominguez, F., A. Valentin-Vargas, J. Chorover, and R.M. Maier.  2011.  Effect of arbuscular mycorrhizal fungi on plant biomass and the rhizosphere microbial community structure of mesquite grown in acidic lead/zinc mine tailings.  Sci. Total Environ. 409:1009-1016. PMC3030643

De-Bashan, L.E., J-P. Hernandez, K.N. Nelson, Y. Bashan, and R.M. Maier. 2010. Growth of Quailbush in acidic, metalliferous desert mine tailings: effect of Azospirillum brasilense Sp6 on biomass production and rhizosphere community structure. Microbial Ecol., 60:915-927. PMC2974781  

De-Bashan, L.E., J-P. Hernandez, Y. Bashan, and R.M. Maier.  2010.  Bacillus pumilus ES4: Candidate plant growth-promoting bacterium to enhance establishment of plants in mine tailings.  Environ. Exper. Bot., 69:343-352.


Grandlic, C.J., M.W. Palmer and R.M. Maier.  2009.  Optimization of plant growth-promoting bacteria-assisted phytostabilization fo mine tailings.  Soil Biol. Biochem., in press.

Hayes, S.M., S.A White, T.L. Thompson, R.M. Maier, and J. Chorover.  2009.  Changes in lead and zinc lability during weathering-induced acidification of desert mine tailings: Coupling chemical and micro-scale analyses.  Appl. Geochem. 24:2234-2245.

Meza-Figueroa, D., R.M. Maier, M. de la O-Villanueva, A.Gómez-Alvarez, A. Moreno-Zazueta, J. Rivera-Castelo, A. Campillo-Castelo, C. Grandlic, and J. Palafox-Reyes.  2009.  The impact of unconfined mine tailings in residential areas from a mining town in a semi-arid environment: Nacozari, Sonora, Mexico.  Chemosphere, in press.

Iverson, S.L., and R.M. Maier.  2009.  Effects of compost on colonization of roots of plants grown in metalliferous mine tailings, as examined by fluorescence in situ hybridization.  Appl. Environ. Microbiol., 75:842-847. PMID: 19047384

Grandlic, C.J., M.O. Mendez, J. Chorover, B. Machado, and R.M. Maier.   2008. Identification of plant growth-promoting bacteria suitable for phytostabilization of mine tailings.  Environ. Sci. Technol., 42:2079–2084. PMID: 18409640

Mendez, M.O., J.W. Neilson, and R.M. Maier.  2008.  Bacterial community characterization of a historic semiarid lead-zinc nine tailings site. Appl. Environ. Microbiol. 74:3899-3907. PMID: 18424534

Mendez, M.O., and R.M. Maier. 2008. Phytostabilization of mine tailings in arid and semiarid environments – an emerging remediation technology.  Environ. Health Perspec. 116:278-283.  PMID: 18335091

Mendez, M.O., and R.M. Maier.  2008.  Phytoremediation of mine tailings in temperate and arid environments. Rev. Environ. Sci. Biotechnol. 7:47-59. DOI 10.1007/s11157-007-9125-4

Rosario, K., S.L. Iverson, D.A. Henderson, S. Chartrand, C. McKeon, E.P. Glenn, and R.M. Maier.  2007. Bacterial community changes during plant establishment at the San Pedro River mine tailings site.  J. Environ. Qual., 36:1249-1259. PMID: 17636285