458
C. Ianni· N. Ruggieri
of the substances (pollutants and others) introduced in the marine environment by
the freshwaters of the Po River. The aim of the work on sediments was to provide information on the distribution, enrichment and speciation of some trace metals in the
surface sediments of two areas of the Adriatic Sea: Chioggia and Ancona. Chioggia
was chosen because of the predominance of fluvial inputs, while Ancona was chosen
because the freshwaters follow the coast until Conero Mount (near Ancona). The examples reported are of course only a part of the work regarding this project (Ianni
et al. 2000).
21.4.1.1
Methods
Total attack. The samples were treated in microwave Teflon vessels with aqua regia and
heated in microwave oven.
Selective extraction. Fraction 1. Exchangeable and carbonates. Ammonium acetate 1 M
(pH 5) was added to the sediment, which was shaken overnight at room temperature.
The extracts were separated from the residues by centrifugation.
Fraction 2. Bound to Fe and Mn oxides. Hydroxylamine hydrochloride 1 M and acetic acid 25% (1:1) were added to the residue, and the same procedure of the first extraction was performed.
Fraction 3. Bound to organic matter and sulphides. The residue of the second extraction was put in a microwave Teflon vessel and after the addition of 8 M nitric acid,
heated in microwave oven.
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.
21.4.1.2
Results
In both areas, metals total concentration are comparable with those found in other
coastal areas of Mediterranean Sea (Donazzolo et al. 1981, 1984; Martincic et al. 1990;
Rapin et al. 1979) and are lower respect to very polluted areas, as for example the Gulf
of Naples (De Rosa et al. 1983). Chioggia presents, for some elements, higher concentrations, due to the relevant input of freshwaters from the Po River.
As regard speciation, in both areas for all the samples, the reducible fraction is poor
of all the elements, and especially of Fe, which should be a major component of the
phase. The negative Eh of these sediments (Colantoni, personal communication) outlines that these sediments are in reducing conditions, particularly rich in sulphides
and organic matter (Fabiano, personal communication) and poor of oxides. Generally, all the elements studied, except Cd and Pb, which are found at some extent in the
labile fraction (exchangeable, carbonates and/or labile organic matter), are associated
prevalently to the oxidizable fraction. This renders the elements in these sediments
not immediately available, but can be released if redox conditions change, for example
for aeration caused by dredging operations.
In Fig. 21.2, the grain size distribution, together with distribution of Pb total content is shown in the area of Chioggia. Beside Pb, even Cd, Sn and Hg present the same
C. Ianni· N. Ruggieri
of the substances (pollutants and others) introduced in the marine environment by
the freshwaters of the Po River. The aim of the work on sediments was to provide information on the distribution, enrichment and speciation of some trace metals in the
surface sediments of two areas of the Adriatic Sea: Chioggia and Ancona. Chioggia
was chosen because of the predominance of fluvial inputs, while Ancona was chosen
because the freshwaters follow the coast until Conero Mount (near Ancona). The examples reported are of course only a part of the work regarding this project (Ianni
et al. 2000).
21.4.1.1
Methods
Total attack. The samples were treated in microwave Teflon vessels with aqua regia and
heated in microwave oven.
Selective extraction. Fraction 1. Exchangeable and carbonates. Ammonium acetate 1 M
(pH 5) was added to the sediment, which was shaken overnight at room temperature.
The extracts were separated from the residues by centrifugation.
Fraction 2. Bound to Fe and Mn oxides. Hydroxylamine hydrochloride 1 M and acetic acid 25% (1:1) were added to the residue, and the same procedure of the first extraction was performed.
Fraction 3. Bound to organic matter and sulphides. The residue of the second extraction was put in a microwave Teflon vessel and after the addition of 8 M nitric acid,
heated in microwave oven.
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.
21.4.1.2
Results
In both areas, metals total concentration are comparable with those found in other
coastal areas of Mediterranean Sea (Donazzolo et al. 1981, 1984; Martincic et al. 1990;
Rapin et al. 1979) and are lower respect to very polluted areas, as for example the Gulf
of Naples (De Rosa et al. 1983). Chioggia presents, for some elements, higher concentrations, due to the relevant input of freshwaters from the Po River.
As regard speciation, in both areas for all the samples, the reducible fraction is poor
of all the elements, and especially of Fe, which should be a major component of the
phase. The negative Eh of these sediments (Colantoni, personal communication) outlines that these sediments are in reducing conditions, particularly rich in sulphides
and organic matter (Fabiano, personal communication) and poor of oxides. Generally, all the elements studied, except Cd and Pb, which are found at some extent in the
labile fraction (exchangeable, carbonates and/or labile organic matter), are associated
prevalently to the oxidizable fraction. This renders the elements in these sediments
not immediately available, but can be released if redox conditions change, for example
for aeration caused by dredging operations.
In Fig. 21.2, the grain size distribution, together with distribution of Pb total content is shown in the area of Chioggia. Beside Pb, even Cd, Sn and Hg present the same