Search

The metal hyperaccumulating species play an important role in soil phytoremediation techniques. The Thesis Project focuses on the development of various methods to improve the ability of nickel phytoextraction in hyperaccumulating species. There are a variety of techniques used for this purpose. This study focuses primarily on the use of agricultural practices to increase the bioavailability of metals in soil, inoculation of plants with microorganisms involved in the process of phytoextraction and external application of growth promoting substances in the plant. Through the development of these techniques is possible to obtain plants with a greater potential for phytoextraction of heavy metals and therefore most likely to use in soil remediation. In this study is also included the study of five different populations of the nickel hyperaccumulator Alyssum serpyllifolium (ssp. lusitanicum and ssp. malacitanum) of the Iberian Peninsula (also known as A. pintodasilvae and A. malacitanum). Different populations included in this study represent the main serpentinitic areas of the Iberian Peninsula: the region of Tras-os-Montes (Morais and Samil) in the northeastern Portugal, Melide in the province of A Coruña, and Sierra de Aguas and Sierra Bermeja, located in the province of Malaga. The main conclusions of this Thesis can be summarised as: - The application of plant growth regulators (PGRs) or phytohormones may increase biomass production of Ni hyperaccumulating species such as Alyssum and Noccaea and, consequently, their metal phytoextraction capacity. The most effective PGR for enhancing Ni removal was the IAA-based product. - Bioagumentation using PGPR can be considered as a potential tool to optimised Ni phytoextraction (or phytomining) technologies, but it remains to be seen whether or not plant-associated microorganisms can further improve the shoot Ni removal on a field scale. This study has identified candidate strains which hence, could be useful for future field-based trials. - There is a great variability in biomass production and Ni accumulation between and within the different A. serpyllifolium populations. A better knowledge of the causes and factors involves in the inter- and intra-population variability in Ni-hyperaccumulating Alyssum species can be an useful tool to select populations more efficient for phytoextraction/phytomining technologies.

Soil contamination with fuel derived organic compounds is a problem principally caused by emissions and residues from the petrochemical industry, traffic accidents, and accidental leaks in pipelines or in underground fuel storage tanks. Soils contaminated with fuels have a high environmental risk, since they can contaminate other environmental compartments, with the inherent risks for human health and for the environment. Sorption to soil particles, volatilization, leaching, degradation (chemical, photochemical and biological oxidation), plant translocation, etc., are the principal processes that will influence on the final fate of soil contaminants in the environment. In order to interpret, evaluate the risks and make decisions about the effects of fuel compounds and assure and adequate protection of the environment, it is very important to understand the toxicology, analytics and the behaviour and fate in the environment. Within this context, the present doctoral thesis has the following objectives: Development of analytical methods for volatile compounds (MTBE, ETBE and BTEX) and diesel range organics (DRO) in soil and water. Application of those methods to the characterization of a site contaminated with hydrocarbons. Study of the dynamics of petroleum contaminants in the soil-plant-water-air system through sorption and leaching experiments and a experiment with root exudates, to study the effect of plants on contaminant mobility through soils. Characterization of gasoline and diesel phytotoxicity, with crop plants bioassays. At last, application of a phytoremediation procedure with Lupinus luteus growing on the A and B horizons of a Cambisol contaminated with diesel (1%, w/w), with the inoculation of best plant growth promoting and degrader bacteria, with the best results from previous experiment. The experiments carried out in this thesis, allowed to obtain a wide knowledge of the behaviour of those contaminants in the soil system, and to predict their final fate in the environment, in addition to their toxic effect once released in soil. The proposed remediation techniques, through bacteria assisted phytoremediation, resulted in a clean, cheap, reliable and highly efficient technique, what predicts satisfactory results in its application to real soils.