Phytoextractors of metal(loid)s of the Italian flora: An Outline

Intensive farming, wastewater irrigation, mining, heavy industry, smelting procedures and improper waste disposal are some of the human activities that contribute to heavy metal soil contamination (Sharma et al. 2007; Khan et al. 2008; Yu et al. 2008). As heavy metals cannot be degraded by microorganisms and tend to remain in polluted sites for long periods of time, soil contamination by heavy metals represents a particular environmental concern and a serious threat to human health. Conventional soil remediation techniques, such as soil washing, excavation, in situ vitrification, solidification and stabilization, can be effectively employed in order to achieve remediation of heavy metal contaminated soils. Anyway, novel approaches are being developed. Some plants are known to be able to uptake and accumulate metals in their above-ground tissues from the soil in which they grow. The exploitation of this ability is termed “phytoextraction” (Salt et al. 1995). We build a first checklist of phytoextrators which are either native or naturalized to Italy, based on international scientific literature. These phytoextractors can be used for bioremediation purposes without the risks related to the use of alien species. In our screening, 169 infraspecific and specific taxa of accumulators were found. These taxa accumulate 18 metals (Nickel, Cadmium, Indium, Barium, Lead, Mercury, Manganese, Thallium, Zinc, Uranium, Gold, Copper, Platinum, Silver, Tungsten, Iron, Aluminum and Chromium), and two metalloids (Arsenic and Antimony). Of these plants, 81 taxa were hyperaccumulators, while the remaining phytoaccumulators could not reach or exceed the hyperaccumulation threshold. 59 of the 169 taxa were species, 5 were subspecies and 5 were varieties, belonging to 52 families. The most represented family was Brassicaceae, with 25 taxa (15%), followed by Poaceae, with 21 taxa (12.65%), Asteraceae, with 20 taxa (12%), Leguminosae, with 12 taxa (7.22%) and Chenopodiaceae, with 8 taxa (4,82%). The analysis of geographical distribution in Italy showed a homogeneous distribution of phytoextractors in the Regions, with a higher number of them in Toscana (133 taxa), Lazio (129 taxa) and Friuli-Venezia Giulia (128 taxa) and lesser number in Valle d’Aosta (82 taxa) and Trentino-Alto Adige (96 taxa). Sicilian flora includes 121 phytoextractors which accumulate all the analyzed metals except for Gold and Silver. Phytoextraction is an emerging technology that can be used to remove heavy metals and/or metalloids from contaminated soils for bioremediation purposes or to extract valuable metals for monetary return as in the case of phytomining. In the last decades Phytoextraction has gained increasing consideration as a reliable, sustainable and low-cost alternative to conventional soil remediation technologies.