Heavy-Metal Phytostabilizing Potential of Agrostis castellana Boiss. & Reuter

The soils of many abandoned mine sites in the central region of Spain are heavily polluted with a number of different metals. Having frequently found Agrostis castellana growing at these old mine sites, this study was designed to assess its remediation capacity for this type of setting. In an initial field study, plant specimens were collected from 4 abandoned mine sites to determine pollutant concentrations in their roots and shoots. This was followed by a 4-year bioassay in a controlled environment in which soils collected from the mines were used to set up microcosms. Maximum root concentrations of the most polluting elements present in the bioassay were 3625 mg kg(-1) Zn, 2793 mg kg(-1) Cu, 13042 mg kg(-1) Pb, 49 mg kg(-1) Cd and 957 mg kg(-1) As. These concentrations represent root bioaccumulation indices of over 1 and usually >2. In contrast, indices of transfer to above-ground phytomass were always < 1, indicating this species is a good candidate for use as a phytostabilizer. However, the high metal concentrations that could reach the above-ground mass of this plant determines a need for close monitoring and avoiding the use of areas under restoration for hunting or grazing.

Phytoremediation of soils co-contaminated by organic compounds and heavy metals: bioassays with Lupinus luteus L. and associated endophytic bacteria

In the central part of the Iberian Peninsula there are old sealed landfills containing soils co-contaminated by several heavy metals (Cu, Zn, Pb, Cd, Ni, As, Cr, Fe, Al, Mn) and organic pollutants of different families (hydrocarbons, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, pesticides and other organochlorinated compounds, phenols and volatile compounds), which this work will address. We have focused on phytoremedial plants that are able to deal with this type of complex pollution, not only species that tolerate the joint effect of heavy metals in the soil, but also those that can take advantage of associated bacteria to efficiently break down organic compounds. This study was carried out with Lupinus luteus and its endophytes in two greenhouse experiments: A) growing in a substrate artificially contaminated with benzo(a)pyrene (BaP), and B) using real co-contaminated landfill soils. Endophytes of roots and shoots were isolated in both bioassays. Plant growth-promotion tests and organic pollutant tolerance and degradation tests were conducted on all strains isolated in bioassay A), and on those proving to be pure cultures from bioassay B). The selected landfill is described as are isolation and test procedures. Results indicate that plants did not show toxicity symptoms when exposed to BaP but did when grown in landfill soil. Some endophytes demonstrated plant growth-promotion capacity and tolerance to BaP and other organic compounds (diesel and PCB commercial mixtures). A few strains may even have the capacity to metabolize those organic pollutants. The overall decline in plant growth-promotion capacity in those strains isolated from the landfill soil experiment, compared with those from the bioassay with BaP, may indicate that lupin endophytes are not adapted to metal concentration in roots and shoots and fail to grow. As a result, most isolated root endophytes must have colonized root tissues from the soil. While preliminary degradation tests showed promising results (some strains exhibiting the potential to use organic pollutants as their sole source of carbon), these are not conclusive and further in-depth degradation assays need to be performed.

Integrated approach to assessing the effects of soils polluted with heavy metals on a plant population

This study addresses the effects of soil polluted with more than one heavy metal in a grass species. A 16-week bioassay with Avena sativa L. was conducted in microcosms using soils from two abandoned mines in central Spain that contained levels above World Health Organization (WHO) reference limits for soils of more than three heavy metals. Pollution effects were examined at cell, tissue, organ, plant and population levels. For this purpose, dry weight, maximum height and number of leaves were determined; leaf tissues were observed by low temperature scanning electron microscopy; the metal contents of roots and shoots were determined by plasma emission spectroscopy and their distribution in different tissues was analyzed by X-ray microanalysis using an environmental scanning electron microscope. The results explain the accumulation and translocation of soil metals by this plant species; their effects in cells, tissues and growth of plants; and allow inference on population effects. The discussion of the methodological approach leads us to propose a valid protocol to assess the effects of a set of heavy metals present in the topsoil of polluted sites on a plant population. We recommend its use for an ecotoxicological diagnosis and risk analysis of similarly polluted sites.