aussa-corno river, marano lagoon, italy

PRESENT
PRESENT AND
AND PAST
PAST INPUTS
INPUTS OF
OF MERCURY
MERCURY
IN
IN A
A SPRING
SPRING RIVER
RIVER ESTUARINE
ESTUARINE SYSTEM
SYSTEM
(AUSSA-CORNO
(AUSSA-CORNO RIVER,
RIVER, MARANO
MARANO LAGOON,
LAGOON, ITALY)
ITALY)
ECSA
41ST INTERNATIONAL
CONFERENCE
S. Covelli1, A. Acquavita2, R. Piani 1, S. Predonzani2, C. De Vittor3
1Dept.
of Geological,
Geological, Enviromental & Marine Sciences,
Sciences, University of Trieste, Italy
Protection Agency of FriuliFriuli-Venezia Giulia (ARPA FVG), Palmanova (Udine), Italy
3National Institute of Oceanography & Applied Geophysics, Dep. of Biological Oceanography, Trieste, Italy
2Environmental
Hg
Introduction and environmental setting
Sampling area
The Marano and Grado lagoon (Northern Adriatic sea)
presents high vulnerability due to the great human impact
caused by urban settlements and industrial areas located
within the AussaAussa-Corno River system.
Torviscosa industrial complex has been a source of mercury
(Hg) since 19491949-50, when a chlorchlor-alkali plant became
operative. Hg discharge presumably stopped in 1984 when
wastewater treatment systems were installed (1).
A total amount of 186.000 kg of Hg was assessed to be
released into the river and, presumably, settled into the
estuarineestuarine-lagoon environment.
The sediments of this lagoon are also affected by a
secondary longlong-term Hg source providing a significant
amount of this metal from the Idrija mine through the Isonzo
river inputs (2,3).
The active input of Hg from the contaminated site into the
lagoon system was determined and special attention was
paid to investigate partitioning of Hg between dissolved and
particulate phases.
Field activity (October 2004)
9 Surface and bottom water samples were collected by Niskin bottle in
ebbebb-tide conditions.
conditions.
9 Temperature, salinity and turbidity were recorded in situ by means of
CTD Hydrolab H2O Multiprobe.
Multiprobe.
station 5
9 Bottom sediments were recovered by a Van Veen grab.
grab.
Analyses
9 Total Hg (THg
), particulate Hg (PHg
(THg),
(PHg)) and dissolved Hg (DHg
(DHg)) in water
Porto Nogaro
industrial site
samples were determined by CV AAS after one step gold amalgamation.
amalgamation.
9 Total Hg in sediments was determined by CV AAS following EPA 3052
recomended digestion method.
method.
9 Dissolved O2 concentrations were determined using the Winkler method.
method.
iver
Corno R
Marano
Lagoon
station 6
Aussa Rive
r
3.78
5.98
9.91
7.16
TSM values (surface and bottom waters) expressed in mg L-1 are also reported
in the salinity-turbidity profiles.
40
PHg (ng L-1)
50
8
dissolved O2 (mg L-1)
10
6
4
surface
bottom
2
0
St. 1
St. 2
St. 3
St. 4
St. 6
130.8
20
3
0
St. 1
St. 5
DHg (ng L-1)
4
0
St. 4
St. 4
St. 6
St. 5
St. 6
surface
bottom
50
-1
PHg (µg g )
5
St. 3
St. 3
60
10
St. 2
St. 2
sampling station
15
St. 1
surface
bottom
10
2
surface
bottom
20
1
30
sampling station
25
Results and Discussion
8.13
15.9
40
Conclusions
20
5
0
St. 1
St. 2
sampling station
St. 3
St. 4
St. 6
St. 5
St. 6
St. 5
sampling station
log Kd
-1
surface
bottom
5.5
5.0
4.5
6
4.0
St. 1
St. 2
St. 3
St. 4
sampling station
St. 6
St. 5
Hg sediment (µg g )
6.5
6.0
ChemicalChemical-physical parameters profiles along the water column (turbidity, salinity, and total
suspended matter) are reported under figure 1. ThermoThermo-haline stratification and saltwedge
system circulation were recognized on the basis of field data. Dissolved
Dissolved O2 decreased
significantly in the bottom saline layer as the saltwedge tip (station
(station 1 and 2) was approached
(2).
The highest surface PHg values were detected in station 1 close to the contaminated site (3).
PHg contents in surface waters decreased towards the rivers mouth,
mouth, probably due to dilution
effects and progressive mixing of riverine and lagoon waters. This
This behavior is even more
evident if PHg concentrations are expressed on the basis of dry weight basis (4).
Conversely, DHg concentrations were almost similar both along the
the river course and between
surface and bottom samples (5).
The higher log Kd values (4.5(4.5-6.0) obtained from surface samples testified that Hg was
prevalently bound to riverine fine suspended particulate matter (6) compared to the more saline
bottom samples.
Values of THg in sediments ranged between 0.820.82-5.69 µg g-1 (7). According to the results, Hg
prevalently accumulated in station 3 and 4 and not at the river mouth (station 6), whereas the
lowest value was found upstream the confluence between Banduzzi channel (passive source)
and the Aussa river (station 2). Moderate Hg content found in the
the Corno River (2.21 µg g-1), not
affected by direct metal inputs, indicates possible influence of tidal fluxes in transport and
sedimentation processes.
30
10
St. 5
station 4
ChlorChlor-alkali plant
4 km inland
7
6
5
4
3
2
1
0
7
St. 1
St. 2
St. 3
St. 4
sampling station
Although direct Hg discharge in the Aussa-River system stopped 20 years ago, a significant
input of Hg, in both dissolved and particulate form, was recently detected in surface
freshwaters. The source can be undoubtedly identified in the artificial channel connecting the
contaminated industrial area and the upper Aussa river course. Contaminated surface
freshwaters flowing from this channel are partially diluted with river waters and mixed with the
more saline lagoon waters nearby the river mouth. These processes would allow Hg to
accumulate not only in the lagoon but also in the lower Aussa River bottom sediments.
Further research will focus on Hg speciation and metal availability in river sediments.
References
(1) REGIONE AUTONOMA FRIULIFRIULI-VENEZIA GIULIA (RAFVG) - USL n. 8 Bassa Friulana, 1991. La qualità
qualità delle acque della Laguna di Marano. Rapporto tecnico, Udine, 101
101 pp.
(2) COVELLI S., FAGANELI J., HORVAT M., BRAMBATI A., 2001. Mercury contamination of coastal sediments as the result of a longlong-term cinnabar mining activity (Gulf of Trieste,
Northern Adriatic sea).
sea). Applied Geochemistry,
Geochemistry, 16: 541541-558.
Background picture is an aerial view of the AussaAussa-Corno river mouth
(thanks to Dr. Sauli & Naturstudio Trieste)
(3) PIANI R., COVELLI S., BIESTER H., 2005. Mercury contamination in Marano Lagoon (Northern Adriatic sea,
sea, Italy):
Italy): Source identification by analises of Hg phases.
phases. Applied
Geochemistry,
Geochemistry, 20: 15461546-1559.