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8 A Multi-disciplinary Challenge for Phytoremediation of Metal-Polluted.. . 143

phytoremediation of Indian mustard (Brassica juncea (L.) Czern) in a site affected
by the toxic spill of pyrite residues at Aznalco ´llar (Spain) was effective only after
the addition of organic matter (cow manure and compost) and amendment with
lime to increase the pH (Clemente et al. 2006). Substantial biomass increases have
also been achieved with sunflower and sorghum after organic or mineral
fertilisation of pyrite waste (Marchiol et al. 2007), suggesting that attention should
be paid to improvements in the physical and chemical properties of the substrate.
In both pyrite and other metal-contaminated wastes, plant growth is limited not
only by contamination but also by several environmental variables, such as unsuit-
able pH, high salinity, insufficient aeration and low water and nutrient availability
(Robinson et al. 2006). In these conditions, extensive root colonisation is essential
for plant establishment and metal acquisition, but root responses under metal
contamination have been investigated in a narrow range of species. For instance,
roots of the hyperaccumulator Thlaspi caerulescens J. & C. Presl. were found to
colonise predominantly Zn-polluted soil regions (Saison et al. 2004), whereas little
information is available for most biomass species. The root system of non-
metallophyte species is expected to be very sensitive to the presence of metals,
with serious damage and growth reduction (Ubi and Osodeke 2007; Rascio et al.
2008). For instance, disruption of the root cuticle, reduced root hair proliferation
and severe deformation of root structures are caused by copper in Chloris gayana
Kunth (Sheldon and Menzies 2005). According to a general rule, which
recommends thorough analysis of polluted sites before the application of any
phytoremediation strategy (Wiegleb and Felinks 2001), the area contaminated by
pyrite waste and metals which we studied was initially characterised for soil
stratigraphy, contaminant distribution and floral analysis.

8.3 Site Characterisation

We focused attention on a contaminated area at Torviscosa (Udine—NE Italy,

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45 49 23 N, 13 16 40 E, 3 m a.s.l.), near an abandoned chemical factory and
within the polluted site ‘Lagoon of Grado and Marano and adjacent rivers’,
which is included in the Italian priority site list for remediation (Fig. 8.1). Pollution
was due to As- and metal-contaminated pyrite cinders, discharged between the
1940s and the late 1970s as by-products of pyrite ore roasting for sulphur extrac-
3
tion. Largely devoid of organic matter, with high bulk density (1.65 g cm ), poor
in nutrients, pH 7.3 (Table 8.1) and relatively low electrical conductivity
1
(0.3 S m ), over the years the cinders had been colonised by sparse spontaneous
2
flora (Coletto et al. 2006). Within a confined area of 2,000 m of the site, total metal
concentrations in the substrate were identified in 2004 in 33 soil samples (2 m deep,
10 m apart); soil stratigraphy was monitored by the digging of six exploratory
ditches (Fig. 8.2). Metals were detected in substrate samples and plant tissues by
ICP-OES (Inductively Coupled Plasma-Optical Emission Spectroscopy) after
microwave-acid digestion. The cinders extended for a depth of 0.7 m over a deep