Heavy metals and arsenic uptake by wild vegetation in the Guadiamar river area after the toxic spill of the Aznalcóllar mine
Introduction
Pollution of the environment with toxic metals has increased dramatically since the onset of the industrial revolution (Nriagu, 1979). The main sources of this pollution are fossil fuel burning, mining and smelting of metalliferous ores, municipal waste, landfill leachates, fertilisers, pesticides and sewage (Forstner, 1995). Toxic metal contamination of soil, streams, and underground water poses a major environmental and human health risk. The threat that heavy metals pose to human and animal health is aggravated by their long-term persistence in the environment (Shaw, 1990). Traditional remedies of soil amelioration are very costly and can only affect the upper layers of the soil.
Populations of a variety of higher plant species are able to colonise these polluted environments, growing in soils in which other plants are not able to live. Plants growing on metal-loaded soils respond by exclusion, indication or accumulation of metals (Baker, 1981). A number of plant species endemic to metalliferous soils have been found to accumulate metals at extraordinarily high levels (>1%) in contrast to normal concentrations in plants. So far, approximately 400 metal hyperaccumulators have been identified (Baker, 1995). The term hyperaccumulator was first used by Brooks et al. (1977) in relation to plants containing more than 1000 mg kg−1 (0.1%) of Ni in dry tissue. It was not until the early 1980s (Chaney, 1983) that it was realised that hyperaccumulators might be used to remediate polluted soils by growing a crop of one of these plants and harvesting it to remove the pollutants. The success of any phytoremediation technique depends upon the identification of suitable plant species that hyperaccumulate heavy metals and produce large amount of biomass using established crop production and management practices. The development of hyperaccumulator plants represents a potential for remediation of soils polluted by heavy metals (Baker et al., 1994). McGrath et al. (1993) reported the results of field trials in which several hyperaccumulators were grown in polluted soils to reduce the soil content of Zn from 440 to <300 μg g−1, the threshold established by the Commission of the European Community (Commission of the European Communities, 1986). Different works about heavy metals and arsenic environmental impact on mining areas have identified some plant species with ability to develop tolerance to these pollutants: Agrostis capillaris (Watkins and Macnair, 1991), Agrostis castellana and Agrostis deliculata (De Koe and Jaques, 1993), Agrostis truncatula (Garcı́a-Sanchez et al., 1996), Cynodon dactylon and Amaranthus hybridus (Jonnalagadda and Nenzou, 1997), Bidens cynapiifolia (Bech et al., 1997), Dittrichia graveolens, Herniaria hirsuta and Verbascum blattaria (Shallari et al., 1998), and Pteris vittata (Ma et al., 2001). The aforementioned works suggested that collecting plant species on contaminated soils may be effective for selecting potential plants to be used in phytoremediation.
On 25 April 1998 a pyrite slurry spill occurred into the Agrio and the Guadiamar rivers (Aznalcóllar, Seville, Southern Spain) which contaminated a wide area (40 km in length, 0.5 km wide) in the proximity of the Doñana National Park, the largest reserve of bird species in Europe. Immediately after the spill, the Autonomous Council of Andalucı́a began soil-reclamation activities in order to reduce the impact caused by leaching of the toxic heavy metals in the affected area to a minimum. After physically removing the sediments the soils remained polluted by trace metals such as Pb, Cu, Zn, Cd, Tl, Sb and As (Simón et al., 1999), and many wild plant species were able to grow in the contaminated lands, despite the high amounts of heavy metals and As present in the soil.
Preliminary results have showed the potential of three plant species collected in the contaminated soils of Aznalcóllar to extract some of the pollutants (De Haro et al., 2000). The present work was undertaken to acquire exhaustive information about the ability of 99 plant species growing wild in this polluted area to accumulate Pb, Zn, Cu, Cd and As, in order to identify metal accumulator species.
Section snippets
Soil and plant sampling
The pyrite mine is located in the village of Aznalcóllar, Sevilla (Southern Spain). Plant sampling was conducted from October 1998 to April 2000 during 30 expeditions to four different locations (Soberbina, Vicario, P241 and Quema) of the affected area. These four locations were chosen in order to cover the variability for soil pH, soil texture, and the degree of the remaining contamination. In addition, soil and plant samples from an uncontaminated area (Córdoba) were collected as a target
Soils
Soil characteristics and trace metal concentration at the five localities tested in this work are given in Table 1. For all the heavy metals studied as well as for As, the locality P241 showed the highest mean concentration.
P241 site showed the widest range for Pb content of all of the contaminated areas, ranging from 103 to 2040 mg kg−1, and the highest mean value of 826 mg kg−1. The lowest mean value for this heavy metal was found in Vicario sampling site with a content of 203 mg kg−1.
Zn
Conclusions
The present work verifies the usefulness of collecting and studying plant species on contaminated soils in order to identify and select those plants with high potential to be used in the remediation of the affected area.
Eleven plant species have been selected for their ability to grow wild on the contaminated soils of Aznalcóllar, and for their efficiency in accumulating one or various pollutants (Table 6).
Also taking into account their high capacities, both to simultaneously uptake several
Acknowledgements
This research was supported by grants from the Consejo Superior de Investigaciones Cientı́ficas (CSIC) and Consejeria de Medio Ambiente (Junta de Andalucı́a). The authors are very grateful to Gloria Fernández (IAS-CSIC, Córdoba) for technical assistance in performing the analyses of plants, and to Dr. Pujadas (University of Cordoba) for his help in botanical determinations. The authors also wish to thank Professor Aguilar, Dr. Simon, and the Department of Mineralogy and Petrology (University of
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2021, ChemosphereCitation Excerpt :The accumulation of metals has been measured in both above- and below-ground parts of the plant and compared with that in the medium (soil or effluent). Among the 23 plant species collected from a site in Spain where pyrite sludge was spilled, P. oleracea was one of the predominant types of vegetation, ranking first and second for the highest Cu and Zn accumulation at the levels of 39 mg Cu/kg and 186 mg Zn/kg, respectively (Del Río et al., 2002). Similarly, among the various metals tested (Cd, Pb, Cu, and Zn) in the above- and below-ground parts of P. oleracea, which were collected from a Pb–Zn mining area in China, Zn was the predominant element accumulated in the shoots (73.1 mg/kg) and roots (129.8 mg/kg) (Wei et al., 2005).