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Title: Phytoremediation and phytomining: Using plants to remediate contaminated or mineralized environments

item Chaney, Rufus
item BAKLANOV, ILYA - University Of Maryland
item CENTOFANTI, TIZIANA - California State University
item BROADHURST, C - University Of Maryland
item BAKER, ALAN - University Of Melbourne
item REEVES, ROGER - University Of Melbourne
item ANGLE, J - University Of Georgia
item VAN DER ENT, ANTONY - University Of Queensland
item ROSEBERG, RICHARD - Oregon State University

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/6/2014
Publication Date: 10/8/2014
Citation: Chaney, R.L., Baklanov, I., Centofanti, T., Broadhurst, C.L., Baker, A.J., Reeves, R.D., Angle, J.S., Van Der Ent, A., Roseberg, R.J. 2014. Phytoremediation and phytomining: Using plants to remediate contaminated or mineralized environments. Chapter 15, In: R. Rajakaruna, R.S. Boyd and T. Harris, editors. Plant Ecology and Evolution in Harsh Environments. New York, NY; Nova Science Publishers. p. 365-391.

Interpretive Summary: Metal contaminated soils are one type of harsh environment which may restrict growth of plants and cause evolution of metal tolerant plants. Research on the evolution of such plants, and consideration of the large land areas contaminated by mine wastes and smelter emissions led to the development of improved methods to remediate or revitalize such contaminated soils. Risk assessment for contaminated soils shows that phytotoxicity from Zn, Ni and Cu can strongly limit growth of most plants on acidic contaminated soils. Risks from Pb and As arise from ingested soil consumed by wildlife, livestock or children. Based on extensive research and testing of methods to remediate these risks, and to achieve persistent revegetation, has led to the new technologies Phytostabilization and Phytoextraction. In phytostabilization, soil amendments are used to convert soil metals to adsorbed, precipitated or occluded forms which have low availability to plants or to animals which ingest soil. Field trials have shown that making mine wastes calcareous and rich in phosphate and other nutrients, especially with application of high rates of organic composts can fully reverse phytotoxicity and infertility of such sites and reduce the bioavailability of soil metals if ingested. Using amendments to achieve phytostabilization allows growth of diverse plant species fit to the local ecology of the site including legumes. Microbes added with the organic amendments inoculate soils and with reversal of the toxicity, allow living soils to support diverse vegetation. In situ phytostabilization is much less expensive than soil removal and replacement, the usual alternative considered by regulatory agencies. An alternative approach uses unusual plants with remarkable ability to accumulate metals called “hyperaccumulators” to absorb metals from soils and accumulate the metals in plants shoots where they can be harvested and removed from the field. The phytoextraction of Cd by rare plants which accumulate 1000-fold higher Cd than common pasture species allows removal of Cd to protect the food chain where risk from soil Cd exists. This is especially important for rice soils because chronic farm family consumption of rice “home grown” on mine waste contaminated soil has caused extensive Cd disease in Asia. Several groups of plants have promise to remove enough Cd to make the rice produced safe for local consumption. For nickel, the value of metal accumulated in the plant shoots is greater than most crop plants, especially considering the severe infertility of such soils where Ni has contaminated or is geologically rich. Because of the value of Ni in the harvest, this is called phytomining rather than simple phytoextraction. Phytomining of nickel has been demonstrated in the field, and has wide application both on mine wastes, smelter contaminated soils, and on arable serpentine soils rich in nickel. These technologies, phytostabilization and phytoextraction, exist because of research conducted over decades to understand better plants adapted to harsh environments, and offer great public savings in dealing with mine and smelter contaminated soils requiring remediation.

Technical Abstract: One type of harsh environment for plants is metal and metalloid contaminated or mineralized soils which exist in most countries due to geological formations or to the history of mining and smelting. Depending on soil pH and fertility, metal-rich soils may be barren and eroding into wider areas. Some elements present risk to humans, wildlife, livestock, plants, or soil organisms and require remediation. The engineering approach of removing the contaminated soil depth is extremely expensive. Thus, alternative methods for in situ remediation of element rich soils have been developed by the agricultural sciences. These methods include phytoextraction (growing plants which accumulate high concentrations of the element in plant shoots for removal from the field), or phytostabilization (adding soil amendments which convert soil elements into forms with much lower phytoavailability and bioavailability which no longer pose a risk to the environment). Phytomining is a variant of phytoextraction in which the element accumulated in plant shoots has enough value to support farming a hyperaccumulator crop to produce a commercial metal bio-ore. This chapter reviews these valuable phytotechnologies which have been developed in the last few decades to reduce the costs of alleviating the environmental risks of contaminated soils.