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Marine Pollution Bulletin 46 (2003) 1015–1023
Persistence of petroleum hydrocarbon contamination in sedimentsof the canals in Venice, Italy: 1995 and 1998
Dana L. Wetzel 1, Edward S. Van Vleet *
University of South Florida, College of Marine Science, 140 7th Avenue South, St. Petersburg, FL 33701, USA
Abstract
Total hydrocarbon and selected polycyclic aromatic hydrocarbon (PAH) levels were examined in sediments collected from
known problematic areas in the canals of Venice, Italy, in 1995 and 1998. Hydrocarbon concentrations were greatest in the interior
canals, moderate in the partially enclosed locations and lowest in the open-water sites. Total hydrocarbon and PAH concentrations
declined from 1995 to 1998. Ancillary data suggest that this decline may have been in response to the elimination of many industrial
activities in the lagoon and to initiating an aggressive canal dredging program. The distributions of individual components were
generally similar both years regardless of the total PAH concentration or the location of sample collected. PAH alkyl homolog
distributions suggest that atmospheric deposition of petrochemical combustion products is the main source of PAHs to Venice�ssediments. In some cases however, the presence of low levels of the two-ring naphthalene homologous series indicate additional low-
level inputs of fresh oil.
� 2003 Elsevier Ltd. All rights reserved.
Keywords: Petroleum hydrocarbons; Pollution; Sediments; Venice; Italy
1. Introduction
The city of Venice, Italy, lies in the Lagoon of Venice
and is connected to the Northern Adriatic Sea through
the port entrances of Lido, Malamocco and Chioggia
(Fig. 1). Over its history, the structure and configuration
of Venice has been altered through human and natural
influences, resulting in a network of numerous canals,which are firmly integrated within the constructs of the
city. More recently, the city and lagoon have undergone
dramatic changes tied to the advent of industrialization
and the associated pollution growth.
The first major industrial zone affecting the lagoon
was established in the 1920s on the mainland at Porto
Marghera, which is located at the end of the 3.5 km
bridge that brought the railroad to the Island of Venicein 1866 (Fig. 1). Concurrently, boats in Venice�s canalsbecame predominately motor driven, further enhancing
contamination coming from the industrialized zone. By
*Corresponding author. Tel.: +1-727-553-1165; fax: +1-727-553-
1189.
E-mail address: [email protected] (E.S. Van Vleet).1 Mote Marine Laboratory, 1600 Thompson Parkway, Sarasota,
FL 34236, USA.
0025-326X/$ - see front matter � 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0025-326X(03)00124-3
the 1960s, a second industrial zone had been created to
the southwest of the first over what had previously been
tidal lands, compounding the effects of human activity
with the addition of more industrial chemicals, petro-
leum and industrial/municipal wastes to the burden of
the lagoon (Lane, 1973).
Today, the Lagoon serves as the drainage basin for
approximately 200,000 km2 and has a population baseof about 1.4 million persons (Van Vleet et al., 1988).
Moreover, the Lagoon of Venice serves as a major oil
transport harbor in Italy. Losses of petroleum from
tankers, commercial and pleasure craft, along with in-
dustrial effluents, agricultural runoff and aerial deposi-
tion, contribute to the much-deteriorated condition of
the marine ecosystem of Venice. About 1200 ships enter
the lagoon annually, of which roughly 60 are large oiltankers transporting crude oil to the area. Within the
last decade, more than 12 million tons of crude oil and
other chemical products have been transported through
the lagoon each year. Since Venice is a major oil port for
Italy, inevitable contamination from the accumulation
of polycyclic aromatic hydrocarbons (PAHs) is a sig-
nificant concern.
The disappearance of animal and plant species is aclear indication of the problems associated with water
Fig. 2. Station locations for 1995 and 1998 studies.
Fig. 1. Location of Venice, Italy in the Venice Lagoon.
1016 D.L. Wetzel, E.S. Van Vleet / Marine Pollution Bulletin 46 (2003) 1015–1023
quality in Venice. Since the 1930s, the diversity of spe-
cies, such as birds, has decreased by 20%, the number of
plant species has declined by 50%, and coverage bymarine eelgrass is down by as much as 80% of its orig-
inal distribution (Salve, 1999). Adequate tidal flushing
of the canals is required to mitigate increased anthro-
pogenic contamination and prevent build-up of con-
taminants in sediments and organisms. In the past,
maintenance of these canals has been inadequate, lead-
ing to high levels of pollutant accumulation. Dredging
of the canals has been attempted as a means of reme-diating the build-up of pollutants. While this strategy
may provide a temporary solution, the long-term success
of dredging is not clear.
Sedimentation is particularly problematic for Venice
due to the strong association of pollutants with fine-
grained sediments, leading to a significant accumulation
of toxic contaminants. Fine-grained sediments provide a
‘‘sink’’ for many contaminants and therefore informa-tion on the long-term accumulation of pollutants. The
more soluble pollutants can be removed by currents or
tidal flow while the insoluble constituents may become
associated with particulate material and ingested by
organisms or deposited in the sediments where they
accumulate. Until the 1980s, virtually no legal regula-
tion of the Porto Marghera industrial area was in place,
and discharges into the lagoon went largely unchecked(Salve, 1999). The potential effects of these pollutants
still remain, since the material was dispersed and de-
posited throughout the lagoon.
The current study examined sediments collected from
known problematic areas in the canals of Venice to as-sess the temporal trends in distributions and concen-
trations of petroleum hydrocarbons in 1995 and 1998.
The sediments were analyzed for total petroleum hy-
drocarbons (TPHs) and selected PAH levels. Diagnostic
techniques such as the distribution of n-alkanes and
PAH homologs were used to help identify potential
sources of hydrocarbons in these environmental sam-
ples. Although some previous studies have investigatedthe distribution of petroleum hydrocarbons in sediments
from the canals of Venice, none have focused on tem-
poral variations of these contaminants for the purposes
of examining the area�s long-term health (Fossato and
Dolci, 1976; Van Vleet et al., 1988).
2. Methods
Sediment samples were collected from eight locations
representing three environmentally different areas within
the canals and lagoon of Venice in 1995 and five loca-
tions in 1998 (Fig. 2). These areas included the interior
canals of Venice, which have limited flushing capacities
and a predominance of fine-grained sediments (stations
23, 24 and 26), the partially enclosed canals with sometidal flushing (stations 2, 8 and 15) and the open-water
locations which had the greatest amount of regular tidal
influences (stations 10 and 11). Surface sediments (ap-
proximately top 5 cm) were collected with a sediment
grab sampler and stored in sterilized glass jars. Addi-
tionally, in the 1995 study, gravity cores from stations 23
and 24 were also collected and sub-samples were taken
from each core at the top (�0–15 cm) and at mid-core(�32–45 cm). Sediments were transported back to the
D.L. Wetzel, E.S. Van Vleet / Marine Pollution Bulletin 46 (2003) 1015–1023 1017
laboratory on ice where they were immediately frozen
until extraction. Sediment sub-samples were taken to
determine moisture content. Approximately 20 g (wet
weight) of each sediment sample were extracted by re-fluxing for 2 h with a fivefold volume excess of 2:1(v/v)
dichlormethane:methanol. Internal standards (5a-androstane and o-terphenyl) were added to each sample
prior to extraction for quantitative hydrocarbon analy-
sis. Following extraction, the organic phase was parti-
tioned with deionized water and separated, and the
extracts were dried over anhydrous sodium sulfate. The
extracts were separated into F1 (aliphatics/saturates)and F2 (aromatics/unsaturates) by silica gel-alumina
column chromatography (Van Vleet et al., 1988). Each
fraction was evaporated to near dryness and redissolved
in hexane for analysis by gas chromatography (GC) and
combined gas chromatography–mass spectrometry
(GCMS). All hydrocarbon fractions were analyzed by
high-resolution GC using a Hewlett-Packard 5890 GC
equipped with a 30 m DB-5 fused silica column andflame ionization detector with hydrogen as the carrier
gas. Oven temperature was held at 50 �C for 2 min and
then programmed from 50 to 280 �C at 6 �C/min and
held at 280 �C for 15 min. Individual compounds were
corrected for detector response factors and integrated
using a Hewlett-Packard data processor. Selected F2
fractions were further analyzed by GCMS for qualita-
tive and quantitative identification of individual PAHsusing a Hewlett-Packard 5971 Mass Selective Detector
under conditions similar to those employed by GC using
helium as the carrier gas. The mass spectrometer was
scanned from mass 40–500 in 0.5 s at an ionization
potential of 70 eV. All mass spectral data were com-
pared to spectra produced by authentic standards and to
Fig. 3. 1995 and 1998 total sediment hydrocarbon concentrations (a
previously published library spectra. The minimum de-
tectable amounts were calculated at 100 ng/g of the ex-
tracted environmental samples.
3. Results
3.1. 1995 sediment samples
Sediments collected from eight locations in the three
different environments, open-water (stations 10 and 11),
partially-enclosed (stations 2, 8 and 15) and interiorcanals (stations 23, 24 and 26), exhibited somewhat
different petroleum hydrocarbon characteristics. Con-
centrations of hydrocarbons were greatest in the interior
canal stations, moderate in the partially enclosed loca-
tions and lowest in the open-water sites with averages
from these three areas of 908, 332 and 145 lg/g dry wt.
respectively (Fig. 3). The mid-core samples from interior
canal stations 23 and 24 had two to three times theamount of total hydrocarbons found in the corre-
sponding surface sediments from these stations. The
unresolved complex mixture (UCM), indicative of
weathering, was significant in samples collected from the
interior canal locations, moderate in the partially en-
closed sites and minimal in the open-water stations (Fig.
4). While biogenic hydrocarbon contributions were
found superimposed onto the UCMs in all the sedimentsamples, the hydrocarbon profiles from the partially
enclosed and interior canal sediments were characteristic
of petroleum contamination with an odd to even pre-
ference of close to unity in each case.
Selected sediments samples were further analyzed
by GCMS for 37 individual PAHs including parent
ll sediments collected from 0 to 5 cm unless otherwise noted).
Fig. 4. 1995 sediment chromatograms: (A) open-water station, (B)
partially enclosed station, (C) interior canal station.
1018 D.L. Wetzel, E.S. Van Vleet / Marine Pollution Bulletin 46 (2003) 1015–1023
compounds and their associated alkyl substituted ho-mologs to determine the amount, distribution and per-
cent composition of the targeted PAHs for diagnostic
source information. The total concentrations of these
selected PAHs ranged from 54 to 160 lg/g dry wt. in the
surface sediments (Table 1). The concentrations of total
PAHs were not significantly different in the surface
sediments of the interior canal stations 23 and 24 and at
the mid-core depth for these samples. While the totalPAH concentrations for the stations varied by location,
the distributions of individual components and percent
compositions were similar regardless of the total PAH
concentration or the location of sample collected (Fig. 5;
distributions are also similar for stations not shown in
figure). The major contributions of PAHs in each of
these sediment samples came from the fluoranthene/
pyrenes (�43%), the phenanthrene/anthracenes (�25%)and the benzo(a)anthracene/chrysene series (�16%;
Table 1).
3.2. 1998 sediment samples
During 1998, sediments were collected from five lo-
cations (Fig. 2) common to the 1995 study representing
the same three types of environments, open-water lo-cation (station 10), partially enclosed site (station 15)
and interior canals (stations 23, 24 and 26) and analyzed
for petroleum hydrocarbons in the same manner as
the 1995 study. The TPH concentrations were lowest in
the open-water station (57 lg/g dry wt.), moderate in the
partially enclosed station (96 lg/g dry wt.) and highest inthe three interior canal stations (average �213 lg/g dry
wt.; Fig. 3). As in 1995, the sediment samples from the
three types of environments had differing intensities of
UCMs. None were evident in the open-water station,
but were significant in the partially enclosed station and
increased in predominance in the interior canal samples,
with UCMs falling in the same general hydrocarbon
range superimposed with biogenic hydrocarbon signa-tures (Fig. 6). Each of these sediment samples were
further analyzed by GCMS for identification and
quantitation of the same 37 selected PAHs as in the 1995
study. Concentrations of the targeted PAHs were fairly
low (7–12 lg/g dry wt.) and consistent in each of the
sediment samples with the exception of the interior canal
station 23, which had a PAH concentration of 81 lg/gdry wt. (Table 2). The dominant PAH contributions seenin each of the sediment samples were from the fluo-
ranthene/pyrenes (�48%), the phenanthrene/anthra-
cenes (�20%) and the benzo(a)anthracene/chryseneseries (�17%). Although the total PAH concentration
was much higher at station 23, the distribution of PAH
homologs was consistent from station to station (Fig. 7).
4. Discussion
Surface sediment samples taken from each of the
three location categories (open-water, partially enclosed
and interior) in both 1995 and 1998 all showed distinct
similarities in hydrocarbon characteristics; however, not
only was there a significant decrease in total hydrocar-
bon concentrations from 1995 to 1998, there was also asubstantial decrease in PAH concentration in all but the
interior canal station 23 which remained the same (Fig.
3; Tables 1 and 2). The range of resolved n-alkanes in
surface sediments was analogous for each of the location
types in each of the two studies with the exception of the
1995 surface sediments from interior canal station 26.
The n-alkane distribution for this station was more
similar to those found in the 1995 mid-core sedimentsamples from the other interior canals than to other
surface sediments collected during that year. Dredging
of surface sediments at this station by the Venice Water
Authority had been completed shortly before our sam-
pling of the surface sediments in 1995. According to the
official plan for dredging, the canal on which station 26
was located was dry excavated (asciutto) from an orig-
inal water depth of 1.38 m to a final depth of 1.90 m fora total of 0.52 m of sediments removed (Commune Di
Venezia, 1984). As a result, the newly exposed surface
sediments (i.e., those collected for our study) were ac-
tually sediments that were roughly at the same original
Table 1
1995 sediments selected PAH composition lg/g dry wt
Station number 2 10 15 23 Top 23 Mid 24 Top 24 Mid 26
Naphthalene <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.2
C1N <0.1 <0.1 <0.1 <0.1 0.3 <0.1 <0.1 0.5
C2N 0.4 <0.1 0.4 <0.1 0.4 <0.1 0.3 1.8
C3N 0.5 0.2 0.9 0.4 0.3 0.1 0.7 1.8
C4N 0.3 0.1 0.6 <0.1 <0.1 <0.1 0.4 1.0
Fluorene 1.5 0.9 2.1 1.8 1.0 0.4 0.3 3.8
C1F 0.7 0.4 1.4 0.6 <0.1 0.2 0.2 1.0
C2F 0.4 0.2 0.9 0.2 <0.1 <0.1 0.2 0.6
C3F 0.4 <0.1 1.0 <0.1 <0.1 <0.1 <0.1 <0.1
C4F <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1
Dibenzothiophene 1.3 0.7 1.8 0.9 0.6 0.4 0.3 1.8
C1DBT 0.4 0.3 1.0 <0.1 0.3 0.2 0.4 0.6
C2DBT 0.4 0.3 0.7 <0.1 1.0 0.2 1.4 1.7
C3DBT 0.3 <0.1 <0.1 <0.1 <0.1 <0.1 2.2 <0.1
C4DBT <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1
Anthracene 13.8 9.5 21.0 14.7 9.7 7.0 2.0 22.4
Phenanthrene 2.8 2.0 6.6 3.6 2.5 2.2 0.5 4.7
C1A+P 3.9 2.9 8.1 3.6 2.5 2.4 0.8 5.4
C2A+P 1.7 1.3 4.0 1.8 1.6 1.0 1.0 3.6
C3A+P 0.8 0.5 1.5 <0.1 1.7 0.3 0.8 <0.1
C4A+P 1.5 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1
Fluoranthene 13.8 11.5 29.2 21.8 21.8 12.1 5.0 39.8
Pyrene 14.0 8.6 27.1 17.3 18.8 8.4 4.3 29.8
C1Fl +Py 6.0 2.7 8.4 4.2 5.0 2.6 1.7 8.5
C2Fl +Py 2.1 1.2 3.3 0.7 1.3 0.9 1.0 2.1
C3Fl +Py 0.4 0.5 1.4 <0.1 <0.1 <0.1 <0.1 0.9
C4Fl +Py <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1
Benzo(a)anthracene 6.6 3.4 3.4 4.5 5.9 3.9 0.8 7.7
Chrysene 6.2 3.0 9.4 4.2 5.3 3.6 1.7 7.5
C1Ba+C 2.8 1.5 4.6 1.0 1.8 1.7 1.0 2.7
C2Ba+C 1.0 0.4 1.6 <0.1 0.4 0.4 0.6 0.6
C3Ba+C 0.4 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1
C4Ba+C 0.2 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1
Benzo(a)pyrene 2.3 1.0 3.9 1.0 1.7 1.4 0.8 2.0
Benzo(e)pyrene 1.8 0.7 2.9 1.2 1.4 1.2 0.8 1.8
Benzo(k)fluoroanthene 5.9 2.4 8.6 2.5 4.5 3.7 1.4 5.8
Dibenzanthracene 0.2 <0.1 0.3 <0.1 <0.1 0.1 <0.1 0.1
Total in lg/g dry wt. 94.8 56.2 156.1 86.0 89.8 54.4 30.6 160.2
% of total F2 HC 53% 56% 68% 60% 26% 39% 11% 48%
D.L. Wetzel, E.S. Van Vleet / Marine Pollution Bulletin 46 (2003) 1015–1023 1019
depth as the 1995 mid-core (�32–46 cm) sediment
samples from stations 23 and 24. In this context, station
26 was not an anomaly and compared well with the two
mid-core samples for both the total hydrocarbon con-
centration and PAH distribution. Mid-core hydrocar-
bon concentrations from the 1995 collections at stations
23 and 24 were considerably higher than the corre-
sponding surface sediments (Fig. 3), however the PAHconcentrations were similar within each core (mid-core
and surface sediments; Table 1), suggesting that much of
the hydrocarbon concentration was attributable to bio-
genic material. The 1995 total PAH concentrations
varied among the stations, ranging from a high of 160
lg/g dry sediment in the surface sediments at station 26
to a low of 31 lg/g dry wt. in the mid-core sediments of
station 24 (Table 1). Again, because station 26 had beendredged prior to this sampling event, the newly exposed
surface sediments did not reflect the 1995 PAH inputs
but instead represented concentrations deposited under
previous environmental conditions. Station 24 was also
included in the overall dredging plan and was dredged in
1997 when 0.81 m of sediments were removed. Decreases
in 1998 total hydrocarbon concentrations and total
targeted PAH concentrations at this station suggest an
improved environmental condition from the previous
1995 study. The total concentration of PAHs in station23 surface sediments remained relatively constant from
the 1995 to 1998 study. This may be explained because
station 23, an internal canal station, was not included in
the dredging plan and is not subject to intensive circu-
lation and tidal flushing.
Surface sediments from each of the stations within
the three location categories during the two sampling
years shared characteristics of n-alkane maxima, percentF1 of total hydrocarbons, percent resolved F1 fractions,
range of the UCMs and, with the exception of station
0
5
10
15
20
25
Nap
htha
lene C1N
C2N
C3N
C4N
Fluo
rene C1F
C2F
C3F
C4F
Dib
enzo
thio
phen
e
C1D
BT
C2D
BT
C3D
BT
C4D
BT
Phen
anth
rene
Anth
race
ne
C1P
C2P
C3P
C4P
Fluo
rant
hene
Pyre
ne
C1P
Y
C2P
Y
C3P
Y
C4P
Y
Benz
o(A)
Anth
race
ne
Chr
ysen
e
C1C
H
C2C
H
C3C
H
C4C
H
Benz
o(A)
Pyre
ne
Benz
o(E)
Pyre
ne
Benz
o(K)
Flu
roan
then
e
Dib
enza
nthr
acen
e
ug/g
dry
wei
ght
Station 10-Open WaterStation 2-Partially EnclosedStation 23 (surface)-InteriorStation 23 (Mid Depth)-Interior
Fig. 5. 1995 sediment PAH concentrations and distributions.
1020 D.L. Wetzel, E.S. Van Vleet / Marine Pollution Bulletin 46 (2003) 1015–1023
26, similar total hydrocarbon concentrations. These
three location categories also shared almost identical
PAH characteristics, not only within the categories, butalso among the whole sample set (Figs. 5 and 7). Each
sample contained significant contributions of the
major PAHs and their homologs, with the dominant
PAHs (anthracene, phenanthrene, fluoranthene, pyrene,
benzo(a)anthracene and chrysene) consistent for every
sample.
Aromatic hydrocarbons from petrochemical com-
bustion sources can be characterized by a lesser degreeof alkylation than aromatics originating from direct
petroleum inputs. This lower degree of alkylation results
from the cleaving of the substituted side chains during
high temperature combustion (Youngblood and Blu-
mer, 1975; Laflamme and Hites, 1978; NRC, 1985).
These homolog distributions can be used to discriminate
petrogenic sources of PAHs from combustion sources.
As was observed in the sediment samples from these twostudies (Figs. 5 and 7), the parent compounds were more
abundant than their homologs. The fluoranthene/pyrene
series were the most abundant PAHs followed by the
anthracene/phenanthrene and benzanthracene/chrysene
series, indicating that combustion-related hydrocarbons
were the key source of PAHs to Venice�s sediments
(NRC, 1985). With the extensive boat traffic on these
canals and the proximity of the industrial plants atnearby Porto Marghera, it is probable that these are the
sources of many of the petroleum hydrocarbons (par-
ticularly the petroleum combustion products) found in
the canal sediments. In some cases however, there were
also low levels of the two-ring naphthalene homologous
series. This is particularly indicative of fresh oil inputs.
Because naphthalene is both highly volatile and soluble
in water (rapidly weathering), the presence of thesePAHs suggests very recent contributions of petroleum to
the environment (Wetzel, 1995). These naphthalene
contributions, while relatively small in comparison to
the other PAHs, suggest that not all the hydrocarbons
are derived from combustion sources since naphthalenes
do not generally survive the combustion process. In-
deed, since motorized boats are the only means of me-
chanical transportation in Venice, accidental spillage,bilge water discharge and oily ballast water containing
petrogenic hydrocarbons are by-products of a commu-
nity whose very culture depends on utilizing the water-
ways for travel. While the hydrocarbon loads found in
sediments in the canals of Venice contain significant
biogenic contributions characterized by odd-numbered
n-alkanes such as nC15, nC17 and nC19, they are gener-
ally superimposed on a characteristic petroleum signa-ture.
Although there was little difference in qualitative
petroleum hydrocarbon characteristics between 1995
and 1998 samples, the total hydrocarbon concentrations
for surface samples collected in 1995 ranged from a low
of 108 lg/g in the open-water sites to a high of 1090 lg/gdry sediment in the interior canals but dropped con-
siderably in 1998 to 57 lg/g in the open-water locationand 294 lg/g dry sediment in the interior station (Fig. 3).
What is important to note here is that not only the total
hydrocarbon concentration decreased from 1995 to
1998, but the percent targeted PAHs of the total hy-
drocarbon load also decreased in each station (Tables 1
Table 2
1998 sediments total PAH concentration and % F2
Station number 10 15 23 24 26
Total in lg/g dry wt. 8.8 10.5 81.0 11.2 7.3
% of total F2 HC 43% 33% 65% 31% 13%
Fig. 6. 1998 sediment chromatograms: (A) open-water station, (B)
partially enclosed station, (C) interior canal station.
D.L. Wetzel, E.S. Van Vleet / Marine Pollution Bulletin 46 (2003) 1015–1023 1021
and 2) except at one of the interior sites (station 23)
which coincidentally was the only interior station not to
have been dredged before the 1998 study, thus suggest-ing that petroleum input sources may have been the
same, but the amount of input appears to have de-
creased. Mid-core hydrocarbon concentrations from the
1995 collections at stations 23 and 24 had considerably
higher total hydrocarbon concentrations than the cor-
responding surface sediments, but the corresponding
PAH content was approximately equal to that found in
the surface sediments indicating that much of the total
hydrocarbon content at mid-core was attributed to large
contributions of biogenic material which, again de-
creased substantially by 1998.
This significant decrease in both total hydrocarbonand petroleum hydrocarbon contamination may be at-
tributable to the aggressive pollution remediation efforts
undertaken by the Venetian government in response to
legislative laws enacted in 1984. One of the many pol-
lution intervention methods established by the Venice
Water Authority includes dredging of most of the canals
within Venice and the industrial areas of Porto Marg-
hera. Two of the interior canal stations (station 24 and26) common to both the 1995 and 1998 studies were
included in the dredging program schedule during these
studies. Data from these studies indicate a reduction in
biogenic inputs to the sediment. This can be attributed
to government efforts to lower nutrient inputs into the
lagoon by creating buffer areas of trees, shrubs and
eelgrass (termed ‘‘estuary phytopurfication systems’’) to
capture agricultural nutrients and associated pollutants.Comparisons to previous sediment petroleum con-
tamination studies can be made with the results from the
current study to assess the degree of contamination that
exists in this sensitive environment. Since Venice does
not currently utilize any extensive wastewater treatment
processes, comparisons to sewage outfalls in other areas
of the world can be drawn to get an idea of how the
direct inputs from Venice compare to a range of envi-ronmental conditions. Although Venice is not a site of
direct sewage outfall or acute petroleum spills, it is an
area of chronic non-point source sewage and pollution
inputs, unique in its environmental characteristics and
condition making it difficult to find suitable compari-
sons.
Sediment hydrocarbon loads found in sewage outfall
areas of Chesapeake Bay (Brown and Wade, 1984) andthe Providence River (Van Vleet and Quinn, 1978)
ranged from 2.4 to 153 lg/g dry wt. and 570 and 5410
lg/g dry sediment respectively. These values, represent-
ing significant anthropogenic inputs, are perhaps indi-
cative of the high-end of systems that experience sewage
and municipal discharges. For low-end natural hydro-
carbon concentrations, examination of non-anthropo-
genically impacted areas can be made. Saliot et al.(1988) investigated ambient levels of hydrocarbon con-
centrations in uncontaminated marine sediments from
the deep-sea region of the Cariaco Trench, and the
Northeastern Atlantic of the Mauritanian and Senega-
lian coasts. In this study, concentrations found in the
sediments ranged from no detectable hydrocarbons to
20.8 lg/g dry sediment. In an earlier study, Van Vleet
and Quinn (1979) found similar levels in uncontami-nated sediments from the Equatorial South Atlantic.
This information helps establish the natural background
(low-end) of hydrocarbon concentrations found in
marine sediments while the sewage discharge studies
0
2
4
6
8
10
12
14
16
18
20
Nap
thal
ene
C2N
C4N
Flu
oren
e
C2F
C4
F
Dib
enzo
thio
phen
e
C2D
BT
C4D
BT
Phe
nant
hren
e
C1P
C3P
Pyr
ene
C2P
Y
C4P
Y
Ben
zo(A
)Ant
hrac
ene
C1C
H
C3C
H
ug/g
dry
wei
ght
Station 10Station 15Station 23Station 24Station 26
Fig. 7. 1998 sediment PAH concentrations and distributions.
1022 D.L. Wetzel, E.S. Van Vleet / Marine Pollution Bulletin 46 (2003) 1015–1023
represent a chronic high-level hydrocarbon contamina-tion condition. The total hydrocarbon concentrations
found in the sediments of the Venice Lagoon in 1995
and 1998 are high compared to the discharge study in
Chesapeake Bay but similar to those found near the
Providence River outfall. This places the Lagoon of
Venice in the same category with highly impacted sew-
age discharge areas.
To further evaluate the significance of the hydrocar-bon levels found in Venice sediments, it is also worth-
while to consider the levels of hydrocarbons found in
marine sediments following an acute oil spill in the
marine environment. For example, in three separate
spills of either crude or refined oil, average sediment
hydrocarbon levels were reported for a 38.3 million liter
spill of medium crude oil in Galeta, Panama (Burns
et al., 1994), the Exxon Valdez tanker loss of 41 millionliters of crude oil (Bragg et al., 1994) and a smaller spill
of 1.2 million liters of Bunker C (no. 6) fuel oil in Tampa
Bay, Florida (Wetzel, 1995). The sediment hydrocarbon
loads ranged from 104 to 105 lg/g dry sediment for the
Panama spill, 103 to 104 lg/g dry sediment in the Exxon
Valdez incident and 101 to 102 lg/g dry sediment in the
Tampa Bay spill. Total hydrocarbon concentrations for
the sediments in the Lagoon of Venice ranged from 102–103 lg/g dry sediment during the current studies. While
the contamination from hydrocarbons in the sediments
in Venice are not as high as in many acute oil spill areas,
the levels found in this study suggest that sediments in
the canals of Venice, Italy are substantially impacted by
anthropogenic petroleum hydrocarbon inputs.
5. Conclusions
The Lagoon of Venice, ancient in origin, complex in
design and fragile in its current ecological condition has
undergone significant deterioration attributable to long-
term anthropogenic impact. Temporal variation studies
and subsequent trend analyses of contaminated envi-
ronments offer a better understanding of the pollution
status of a complex ecosystem, particularly in areaswhich are attempting systematic remediation of im-
pacted areas.
Three different types of environments were identified
in the Lagoon of Venice: open-water sites, partially en-
closed canals and interior canals. These three environ-
ments were classified by different amounts of flushing
and tidal influences which affect the concentration of
contaminants deposited in the sediments. Petroleumcontamination in the lagoon has been problematic for
several decades due to the industrialization of Porto
Marghera and to the increase in motor-boat traffic in the
canals. Diagnostic chemical techniques for assessing
petroleum components suggest that the existing con-
tamination can primarily be attributed to atmospheric
deposition of petroleum combustion products, with
smaller amounts from fresh oil inputs probably due toboat traffic. Both the TPH and the total PAH concen-
trations appeared to decline from the 1995 to 1998 in
each of the three environments. This decline in petro-
leum contamination may very well be in response to the
elimination of many industrial activities in the lagoon
and to the aggressive canal dredging program initiated
D.L. Wetzel, E.S. Van Vleet / Marine Pollution Bulletin 46 (2003) 1015–1023 1023
by the Venice government. Continued progress on the
restoration of the lagoon environment enhanced by
public and scientific awareness and assessment may
prove to successfully arrest the rapid deterioration of thelagoon and help restore it to a stable and productive
environment.
Acknowledgements
Funding for this work was provided by Italy�sConsiglio Nazionale delle Ricerche Short-term ForeignExchange Fellowship Program and by the Gladys
Krieble Delmas Foundation. We are greatly indebted to
the administration and scientists at the Istituto di Bio-
logia del Mare for their hospitality and assistance. We
especially appreciate the scientific collaboration and
viticultural interactions with Dr. Valentino Fossato,
Dr. Giancarlo Campesan, Dr. Danieli Cassin and Mr.
Francisco Dolci.
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