Feasible biotechnological and bioremediation strategies for serpentine soils and mine spoils

EJB Electronic Journal of Biotechnology ISSN: 0717-3458 © 1999 by Universidad Católica de Valparaíso - Chile Vol.2 No.1, Issue of April 15, 1999. Received February 9, 1999/Accepted April 7, 1999 REVIEW ARTICLE Feasible biotechnological and bioremediation strategies for serpentine soils and mine spoils Majeti Narasimha Vara Prasad1 Departamento de Botânica, Faculdade de Ciências e Tecnologia da Universidade de Coimbra, 3000 Coimbra, Portugal Permanent address: Department of Plant Sciences, School of Life Sciences University of Hyderabad, Hyderabad 500046 Fax: +91-040-3010120/3010145 Email: Helena Maria De Oliveira Freitas Departamento de Botânica, Faculdade de Ciências e a Tecnologia da Universidade de Coimbra, 3000 Coimbra, Portugal Fax: 351-039-820780, Tel: 351-039-822897 E-mail: Reclamation of metalliferous areas is a priority field of biogeochemistry of trace elements. Ultramafic outcrops rich in heavy metals have been mapped in different parts of the world. Heavy metals are potentially cytotoxic, caricinogenic and mutagenic. Environment protection agencies and legislations insisting the mine operators to restore the mine spoils and tailings since the metal leachates have serious implications in production of healthy agricultural products. Hence, restoration of mine spoils, tailings and metalliferous soils is a challenging task for the well being of Humans. Synthetic and natural zeolites have been used as chelators for rapid mobility and uptake of metals from contaminated soils by plants. Use of synthetic chelators significantly increased Pb and Cd uptake and translocation from roots to shoots facilitating phytoextraction of the metals from low grade ores. Contrastingly, synthetic cross linked polyacrylates, hydrogels have protected plant roots from heavy metals toxicity and prevented the entry of metals into roots. However, application of these synthetics on large scale may not be a practical solution due to exorbitant costs. Therefore, introduction of metal tolerant wild plants to metalliferous soils, genetic engineering of plants for enhanced synthesis and exudation of natural chelators into the rhizosphere, improvement of the rhizosphere with the help of mycorrhiza and integrated management of the metalliferous ecosystem following the principles of phytoremediation are discussed in this paper. The term “serpentine” is applied to minerals viz, lizardite, antigorite and chrysotile (= well known in asbestos-form in some areas). The famous Roman military surgeon Dioscorides recommended it for the prevention of snakebite or the rocks 1 have the speckled colour of serpents. Serpentinized rocks are distributed all over the world viz., western north America; New foundland, Mount Albert in eastern Canada; Lizard peninsula, Wales and Scotland; north-east Cuba; Portugal; Italy; Balkan peninsula; Turkey; topical far east; Central Brazil; New Caledonia; south east Asia; Philippines; Japan; Zimbabwe; eastern Transvaal Loweveld of South Africa, New Zealand; greenstone belts of western Australia In north-east of Portugal the serpentinized area is about 8,000 ha with characteristic geology and flora. The soils contain low N, P, K, Ca, K, Mo and high Cr, Co, Ni and Mg/Ca quotient. The ecology and floristics of this region has been investigated by Sequeira and Pinto da Silva (1991). For the convenience of readers, the slient serpentinophytes are shown in table 1 and figure 1. The Ni content in leaves analyzed from the herbarium specimens of endemics, endemicPoaceae, and non-endemics of north-eastern Portugal are shown in figures 2-4 respectively. By proper understanding of the chemical (pH, Eh, CEC, metal speciation), physical (size, texture, clay content, % organic matter), and biological (flora and microorganisms) processes and their interactions, it is possible to initiate appropriate bioremediation measures. The conventional remediation technologies (other than bioremediation) used for in situ and ex situ remediation are typically expensive and destructive. The include solidification and stabilization, soil flushing, electrokinetics, chemical reduction/oxidation, soil washing, low temperature thermal desorbtion, incineration, vitrification, pneumatic fracturing, excavation/ retrieval, landfill and disposal (Saxena et al 1999; Wenzel et al 1999). Corresponding author This paper is available on line at http://www.ejb.org/content/vol2/issue1/full/5 Environmental biotechnology feasible biotechnological and bioremediation strategies for serpentine soils and mine spoils Table 1. Important European serpentinophytes (Sequira and Pinto da Silva 1991) Genus Species Portuguese taxa Alyssum Anthyllis Arenaria Armeria Asplenium Centaurea Cerastium Cytisus Dianthus Euphorbia Festuca Fumana Ionopsidium Koeleria Minuartia Onosma Plantago Podospermum Potentilla Scorzonera Semppervivum Seseli Silene Stachys Stipa Thymus Veronica (8) (3) (5) (8) (2) (4) (8) (2) (6) (4) (4) (2) (2) (3) (3) (3) (3) (1) (6) (4) (3) (3) (8) (3) (3) (3) (2) A. pintodasilvae A. sampaiana A. tetraquetra sub. sp. fontiqueri A. eriophylla, A. langei, A. daveaui A. cuneifolium Figure 1. Number of Serpentinophytes in Europe and Portugal (see also table 1 and 4) D. marizii F. brigantina I. abulensefo K. crassipes P. radicata var. radicata P. tenuifolium S. hispanica var. asphodeloides S. peixotianum S. legionensis Bioremediation, is an integrated management of polluted ecosystem where different organisms are employed which catalyze the natural processes in the polluted or contaminated ecosystem (aquatic or terrestrial). Suitable, but high cost technologies have been identified for clean-up of heavy-metal-polluted soils (Iskandar and Adriano 1997). Recently, the potential role of bioremediation, particularly higher terrestrial plants (phytoremediation) in remediation of metal-polluted soils has been studied by an increasing number of scientists from various disciplines including plant scientists, microbiologist, chemists, soil scientists and geologists owing to its commercial importance (Raskin 1995; Watanabe 1977). Emerging phytoremediation technologies suitable for metal contaminated ecosystems and the integral processes involved 37 Prasad M., De Oliveira H. and relevance to contemporary environment have been comprehensively reviewed (Saxena et al. 1999; Wenzel et 1999). Recently, Hüttermann and co-workers have used cross linked polyacrylates, hydrogels (Stockosorb K400), to metal-contaminated soils. When Stockosorb K400 was applied to hydrocultures of Scots Pine, Pinus sylvestris, which contained 1 mM of Pb, the hydrogel increased the nutrient efficiency of the plants and, the detrimental effect of the heavy metal was completely remediated (Hüttermann et al. 1999 in Prasad and Hagemeyer 1999). Hydrogel significantly inhibited the uptake of Pb by the fine roots of 3-year-old spruce. Conversely, Anderson et al (1998) have induced Brassica juncea to accumulate gold from ores by treating the substr (...truncated)