464
C. Ianni· N. Ruggieri
perature for one hour, then treated at 50°C in an ultrasound bath for two hours. A further aliquot of hydrogen peroxide was added, and the vessels were heated in a microwave oven. After cooling, 2 M ammonium acetate (pH 2) was added, and the procedure was carried out as for Steps 1 and 2.
The metal content of the residual phase was obtained by the difference between
the total content and the sum of the Fractions 1, 2 and 3.
21.4.2.2
Results
In this area, total metal content is generally lower than or similar to natural levels,
except for Cr and Zn in all samples, and for Pb and Cd only in some particular stations. No fluvial inputs interest this part of the coast, and as it can be seen by the distribution of the fine fraction «63 flm) in Fig. 21.7, near the coast we find a high amount
of coarse particles, while the fine particles are found off-shore.
Prior to analysis, the sediments were subdivided in two granulometric fractions
« and >63 flm). All the metals in the >63 flm fraction present increasing gradients
towards off-shore; in the <63 flm fraction the elements have the same trend (in Fig. 21.7
distribution of Cu is reported as an example), except Cd and Pb, which present an
opposite behaviour, as shown in Fig. 21.7 for Pb.
Selective extractions, which were performed on the fine fraction, indicate for Cd and
Pb in the area where their concentration is higher (Transects 4 and 6), indicate that both
are present, Pb in all stations and Cd in the coastal ones, in the oxidizable fraction
(see Fig. 21.8). This phase is not easily mobilizable, but can be oxidized in different
environmental conditions. Moreover, Cd is present in the more available fraction, with
increasing percentages from the coast towards the open sea. Nevertheless, considering the small percentage of fine fractions in this zone, the concentration of heavy metals
in the bulk of the sediment is still low. At any rate, these results outline an evident coastal
input, probably associated to organic matter, not present for the other elements.
In all the other cases, selective extractions outlined that metals are present in very
low amounts in the three fractions extracted and up to 80% in the residue. As an example, speciation of Cu and Cr in two transects where their total content was particularly high is reported in Fig. 21.9.
As far as this set of data can indicate, these sediments don't seem particularly polluted, even if in some cases variations in physical and chemical conditions can cause
negative impacts on the environment. Even in this case, these are some examples drawn
from the work, which being still in progress, foresees other sampling and analysis. It
will be interesting, for example, to evaluate the results of selective extractions performed on the coarse fraction, which in some cases presents higher contents with respect to the fine fraction.
21.S
Conclusions
The case studies reported confirmed that selective extractions are a very useful and
versatile technique to investigate on environmental impact, bioavailability and metal
origin in marine sediments. Obviously, for a complete understanding of enrichment,
C. Ianni· N. Ruggieri
perature for one hour, then treated at 50°C in an ultrasound bath for two hours. A further aliquot of hydrogen peroxide was added, and the vessels were heated in a microwave oven. After cooling, 2 M ammonium acetate (pH 2) was added, and the procedure was carried out as for Steps 1 and 2.
The metal content of the residual phase was obtained by the difference between
the total content and the sum of the Fractions 1, 2 and 3.
21.4.2.2
Results
In this area, total metal content is generally lower than or similar to natural levels,
except for Cr and Zn in all samples, and for Pb and Cd only in some particular stations. No fluvial inputs interest this part of the coast, and as it can be seen by the distribution of the fine fraction «63 flm) in Fig. 21.7, near the coast we find a high amount
of coarse particles, while the fine particles are found off-shore.
Prior to analysis, the sediments were subdivided in two granulometric fractions
« and >63 flm). All the metals in the >63 flm fraction present increasing gradients
towards off-shore; in the <63 flm fraction the elements have the same trend (in Fig. 21.7
distribution of Cu is reported as an example), except Cd and Pb, which present an
opposite behaviour, as shown in Fig. 21.7 for Pb.
Selective extractions, which were performed on the fine fraction, indicate for Cd and
Pb in the area where their concentration is higher (Transects 4 and 6), indicate that both
are present, Pb in all stations and Cd in the coastal ones, in the oxidizable fraction
(see Fig. 21.8). This phase is not easily mobilizable, but can be oxidized in different
environmental conditions. Moreover, Cd is present in the more available fraction, with
increasing percentages from the coast towards the open sea. Nevertheless, considering the small percentage of fine fractions in this zone, the concentration of heavy metals
in the bulk of the sediment is still low. At any rate, these results outline an evident coastal
input, probably associated to organic matter, not present for the other elements.
In all the other cases, selective extractions outlined that metals are present in very
low amounts in the three fractions extracted and up to 80% in the residue. As an example, speciation of Cu and Cr in two transects where their total content was particularly high is reported in Fig. 21.9.
As far as this set of data can indicate, these sediments don't seem particularly polluted, even if in some cases variations in physical and chemical conditions can cause
negative impacts on the environment. Even in this case, these are some examples drawn
from the work, which being still in progress, foresees other sampling and analysis. It
will be interesting, for example, to evaluate the results of selective extractions performed on the coarse fraction, which in some cases presents higher contents with respect to the fine fraction.
21.S
Conclusions
The case studies reported confirmed that selective extractions are a very useful and
versatile technique to investigate on environmental impact, bioavailability and metal
origin in marine sediments. Obviously, for a complete understanding of enrichment,