Gentle remediation at the former “Pertusola Sud” zinc smelter: Evaluation of native species for phytoremediation purposes
Introduction
Poorly regulated metal processing industries and inefficient industrial processes resulted in sites contaminated with metals and metalloids (Clemente et al., 2008). The traditional soil clean-up treatments are based on chemical and physical approaches (e.g. solidification and stabilization, soil washing, electrokinetics, redox reactions). Such treatments are usually costly, power consuming and may negatively impact soil structure and functions (Wu et al., 2010).
A number of alternative techniques utilize an in situ, low-invasive approach where plants are used for reducing contaminant transfer to the environment by direct extraction of pollutants (clean up) or their stabilization (inactivation). Collectively, these techniques may be referred to as “gentle remediation” (GR) options (Onwubuya et al., 2009).
A gentle remediation approach comprises two main options (ITRC, 2009). (i) Phytoextraction, typically used to tackle metals, metalloids and radionuclides, involves the use of plants to remove contaminants from soil. The metals accumulated in the aerial parts can be removed by harvesting and burning the biomass to recover metals. (ii) Phytostabilization is a mechanism that immobilizes pollutants – mainly metals – within the root zone, by adsorption, chelation and precipitation of metal ions, thus preventing migration of contaminants by erosion, leaching and runoff.
Phytostabilization might be often considered as a provisional solution until other techniques become affordable. However, for large contaminated sites (e.g. related to mining or industrial activities), phytostabilization is probably the only reasonable option to restore ecosystems (Schwitzguébel et al., 2009).
Gentle remediation options are ultimately based on soil-plant relationships (Chaney et al., 2007). Thus, both soil characterization and knowledge of plant traits are fundamental elements to evaluate the efficiency of a soil clean-up project a priori. With regard to plant species, it should always be considered that the ecological pressure due to soil pollution must be at least counteracted by using metal tolerant species adapted to the local conditions. For this reason, the phytoremediation potential of native plants colonizing the polluted site must be evaluated (Bidar et al., 2007, Nedunuri et al., 2009, Jiménez et al., 2011) prior to choosing other species to be used in GR. Such plants are able to perform better than other species in terms of survival, growth and reproduction as they are already adapted to the local climate and polluted soils (Yoon et al., 2006).
From 1930 onwards, “Pertusola Sud” carried out electrolytic zinc smelting by processing concentrated raw material (i.e. sphalerite, ZnS). The industrial process produced refined Zn, Cd, Ge and In. Production ceased in 1999. The soil within the whole area of the industrial plant is heavily polluted by several trace elements. At present, the industrial site is included within the perimeter of the polluted area named ‘Crotone-Cassano e Cerchiara’ identified as a site of national interest by the Italian Ministerial Decree 468/2001 ‘National Programme for Environmental Restoration of Polluted Sites’. The company has drawn up a master plan for the clean-up of the whole polluted site. GR options were considered for a specific area where both by-products and wastes had been disposed of in the past. A gentle remediation approach was chosen mainly to reduce the cost of soil remediation. However there is another important reason. The area is rich in archaeological finds. A campaign of archaeological investigations conducted in the mid-1970s demonstrated that a part of the industrial area lies on the site of the northern district of Kroton, an ancient city of Magna Graecia that was founded around the year 710 BC (Cavagnaro Vanoni and Linington, 1977).
A polluted industrial site in which ancient settlements are hidden underground appeared to be a paradigmatic scenario that necessarily requires GR for soil clean up.
With the ultimate goal of designing a GR project, some preliminary investigations were done on the contaminated site. The overall objectives of this research were: (i) to determine the concentrations of trace elements in plants spontaneously growing on a contaminated site, (ii) to compare metal concentrations found in the aboveground biomass to those in roots and in soils, and (iii) to assess the feasibility of using these plants for phytoremediation purposes.
Section snippets
Site description and sample collection
This study was conducted in Crotone, S Italy (39°05′09″N, 17°07′06″E and 6 m above sea level) within the former Zn smelter “Pertusola Sud” property. The full site is about 50 ha divided in different working sectors. Our investigation was carried out at “Area Sottoprodotti” (By-products Area). This site is about 5 ha and was used in the past for the disposal of industrial wastes. The climate is Mediterranean, with a mean annual temperature of 17.4 °C and an average annual rainfall of 681 mm (Bellecci
Ecology of native species
The whole surveyed area consists of an environmental mosaic of artificial tree plantation and pioneer communities. The herbaceous species sampling areas (A–D in Table 1) are ascribable to four sub-nitrophilous plant communities characterized by different water availability and dynamical stage. Area A is an open scrub vegetation of shallow damp sandy loam soil. The herbaceous stand is discontinuous with high cover of tall hygro-nitrophilous perennial species such as S. holoschoenus and P.
Conclusions
This study was conducted to screen plants growing on a heavily polluted industrial site to determine their potential for phytoremediation purposes. Multi-element contaminated soils contain several pollutants, so it is necessary to screen out plants that can accumulate different pollutants simultaneously.
According to the field investigation, despite the condition of severe soil multi-metal contamination some plants could vegetate and absorb a wide range of soil metals (Cd, Cu, Ge, Hg, In, Pb, Tl
Acknowledgment
This work was supported by Lande srl.
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