Description of the Sampling and Analytical Methods Used

Composite samples consisting of five subsamples were taken from the plots after 24 months of adding amendments, as well as from a control plot. Soil pH was determined for a water/soil ratio of 1:1 (Peech 1965), and the electrical conductivity of each saturated extract was measured (Bower and Wilcox 1965). Total nitrogen was determined using the Kjeldahl method (Duchaufour 1970), and organic carbon was analyzed using a total organic carbon analyzer (TOC-V CSH, Shimadzu). The equivalent calcium carbonate was determined using a Bernard calcimeter.

Total Pb concentrations were determined using HNO3/HClO4 digestion at 210°C for 1.5 h (Risser and Baker 1990). DTPA-extractable Pb (considered to be the bioavailable Pb) was determined according to Lindsay and Norvell (1978) and Norvell (1984). Metal concentrations were measured using AAS (UNICAM 969).

15.2.3.1 First Stages of Phytostabilization

Plant cover was assessed on each plot after 24 months of amendment addition, and plant species identification was also carried out. The Pb content in the aerial part of the dominant plant species, Diplotaxis lagascana, was analyzed in order to assess Pb accumulation and the risk of its mobilization through the food chain. Plants were harvested before the start of the senescence phase, and one representative sample per plot was obtained by combining five individual plants. Plant samples were washed with deionized water and dried at 60°C during 24 h. Afterwards, the samples were ground and incinerated at 480°C for 24 h and then diluted with 25 ml HNO3 (65%).

Finally, a study related to the selection of the most suitable species for future activities in the phytostabilization program was carried out.

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