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proportion of clayey material, as reported by Buscaroli et al. (2009). Compared to
other data available from the area, referred to deeper and older sediments that include
either fine or coarse grained sediments (Amorosi et al., 2002; Curzi et al.
2006), Pb and Zn display wider ranges and highest maxima suggesting anthropogenic
contribution for these elements. In the GP1 profile, the higher concentrations
occur down to 25 cm depth, thus suggesting a diffuse migration of Pb and Zn elements
to deeper horizon. All other elements, except for only one sample having
high Cu concentration in PER2 profile, are within the ranges observed for reference
borehole data.
Geoaccumulation index (Igeo) has been calculated for each metal (Table 2) in order
to evaluate metals contamination in soil samples from the Ravenna area.
Geoaccumulation index was originally defined by Müller (Müller, 1979; Forstner
and Müller, 1981) as a quantitative tool to determine metals contamination in
sediments and is based on the comparison of current concentrations with preindustrial
levels. Geoaccumulation index (Igeo) can be calculated by the equation:
Igeo = log2 [Cn/(1.5·Bn)] (1)
where Cn = metal concentration in the the topmost sample; Bn = metal concentration
in the 80-100 cm sample. In this way each site has a different background values
but it helps because of the difference in grain size that affects EPT abundance.
In any case the concentration in the deep samples are comparable with those of
boreholes of analogous grain size as already pointed out.
Müller has distinguished seven classes of sediments: unpolluted (Igeo 0), from
unpolluted to moderately polluted (0 < Igeo < 1), moderately polluted (1 < Igeo < 2),
from moderately to strongly polluted (2 < Igeo < 3), strongly polluted (3 < Igeo < 4),
from strongly to extremely polluted (4 < Igeo < 5), extremely polluted (Igeo > 5).
According to these scheme the Pb is most critical element suggesting moderately
polluted conditions in the san Vitale pinewood in both transects with the soil profiles
near to industrial settlement (PW1 and PW8) and for the Ravenna urban park.
The most likely origin is related to emissions from vehicle exhaust that have been
concentrated in these sites characterized by limited or absent reworking. There
appears to be moderate pollution for copper in the PER2 site, for the reasons already
outlined.
Table 2 – Values of the Igeo calculated according to Müller (1979). Only positive values
were reported.
Transect
Soil
profile Ba Cr
Geoaccumulation index Igeo
Cu Ni Pb V Zn
PW-North
PW1
PW4
0.6 1.9
0.6
0.5
PW-South
PW6
PW8
0.7
2.0 0
1.1
0.7
GP GP1 1.3 0.2
PER PER2 1.4
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