The Venice Lagoon is subjected to long-range transport of contaminants via aerosol from the near Po Valley. Moreover, it is an area with significant local anthropogenic emissions due to the industrial area of Porto Marghera, the urban centres, and the glass factories and with emissions by ships traffic within the Lagoon. Furthermore, since 2005, the Lagoon has also been affected by the construction of the MOSE (Modulo Sperimentale Elettromeccanico—Electromechanical Experimental Module) mobile dams, as a barrier against the high tide. This work presents and discusses the results from chemical analyses of bulk depositions, carried out in different sites of the Venice Lagoon. Fluxes of pollutants were also statistically analysed on PCA with the aim of investigating the spatial variability of depositions and their correlation with precipitations. Fluxes of inorganic pollutants depend differently on precipitations, while organic compounds show a more seasonal trend. The statistical analysis showed that the site in the northern Lagoon has lower and almost homogeneous fluxes of pollutants, while the other sites registered more variable concentrations. The study also provided important information about the annual trend of pollutants and their evolution over a period of about five years, from 2005 to 2010.
Average annual mass fluxes of atmospherically deposited dust are estimated at 8, 12, and 35 g·m−2 in the Western Mediterranean (WMED), Central Mediterranean (CMED), and Eastern Mediterranean (EMED), respectively [
The aim of the present work is to investigate the spatial variability of depositions in the Venice Lagoon, its correlation with precipitations, and the possible impact of the construction of the MOSE dams, by studying the fluxes of inorganic and organic pollutants in the areas next to the construction sites. Our study also provides precious temporal information about the presence of contaminants in the atmosphere of the Lagoon.
Samples of bulk depositions cover a temporal range of about 5 years, from July 2005 to March 2010. The sampling was not a continuous activity; nevertheless, more than one hundred sample campaigns were carried out during this period in six sites located in different areas of the Venice Lagoon. Sampling sites were connected to the three Lagoon inlets and next to the MOSE construction yards. Each campaign lasted 32 days on average, at the end of which the related sample of bulk deposition was collected.
The positions of the samplers are shown in Figure
Maps of the sites of the deposimeters.
In order to study the contribution of construction activities to the atmospheric pollution of the area, by determining the principal organic and inorganic pollutants in depositions, four samplers were placed next to the Lido inlet, at different distances from the construction site: the deposimeter D1, which was located within the construction area, recorded direct emissions from its activities; D2 was located several hundred metres from D1, on the seafront; D3 was placed at the same distance from D1 but four metres above the ground to avoid the influence of local events; D4 was located at a distance of 2 km from the construction site, in an area not affected by local traffic (Figure
Precipitation data, when available, were registered from a meteorological station located near the sampling site D4 provided by the ARPAV (Veneto Regional Agency for Environmental Prevention and Protection). The precipitation data collected by the recording rain gauge Ceppe located near the sampling site D5, provided by MAV (Ministero delle Infrastrutture e dei Trasporti Magistrato alle Acque di Venezia—Italian Ministry of Infrastructure and Transport), were also considered.
The precipitation daily data were integrated during the period of the depositions’ exposure, with the aim of investigating the relation of precipitation with the fluxes of contaminants.
Bulk depositions were collected into 1-meter-high passive stainless steel samplers, composed of two cylindrical supports and two vessels—one made of polyethylene and the other of glass—suitable for the simultaneous determination of inorganic and organic pollutants. The polyethylene vessel, which was used for the determination of inorganic pollutants, was repeatedly washed with Milli-Q water at 2% HNO3 Suprapur; the glass vessel, which was used for the determination of organic pollutants, was repeatedly washed with organic solvents. At the end of each sampling time, the depositions were measured with a graduate glass and stored into vessels made of LDPE (low density polyethylene) (for the analysis of inorganic contaminants) or glass (for the determination of organic contaminants). The remaining particulate matter adhering to the surface of the sampler’s vessels was collected by filters made of mixed cellulose esters (for the determination of inorganic contaminants) or quartz fibre (for the determination of organic contaminants). Moreover, at the end of each sampling time, a blank was also collected by washing the sampler’s vessel with Milli-Q water and by cleaning the vessels’ surface with filters.
Analyses of organic pollutants were carried out in the CSMO (Centro Studi Microinquinanti Organici—Study Centre of Organic Micropollutants) laboratory in Voltabarozzo, Padua, Italy. The water samples used for the analysis of organic pollutants were treated by continuous liquid-liquid extraction to obtain organic samples using a mixture of hexane-dichloromethane (1 : 1); the particulate matter collected with filters was extracted by a sonic bath, using a mixture of pentane-dichloromethane (2 : 1) in a closed flask. The two mixed extracts were dehydrated with anhydrous sodium sulphate, and the volume was reduced to 5 mL under a nitrogen flow at 23°C (Turbovap II Zimark) and cleaned using an automated multicolumn system (Power-Prep, Fluid Management System Inc.). The resulting samples were loaded onto a packed neutral silica column (flow: 2 mL min−1) previously conditioned with 50 mL of n-hexane (flow: 10 mL min−1) and then eluted with 30 mL of n-hexane (flow: 10 mL min−1) followed by 30 mL of n-hexane/dichloromethane (1 : 1; flow: 5 mL min−1). The final volume was reduced to 500
Before extraction, carbon-13-labelled IPA (phenanthrene) was added to the extracts as internal standard. The samples were checked for external contamination by analysing the blanks. The samplers were cleaned twice using filters and 125 mL of dichloromethane: the analysis of the dichloromethane and the filters constituted the blank. LOD was calculated from the average value of the blanks, plus three standard deviations, while the precision was evaluated by four analyses of a water sample spiked with a known quantity of PAHs.
Gas chromatographic separation was performed with a fused silica capillary column (J&W Scientific DB-5MS, 60 m × 0.25 mm O.D. 0.25
Each filter was digested by microwave (Ethos1-Milestone) inside a Teflon vessel (100 mL) held in a 10-place high-pressure carousel (Milestone HPR-1000/10S High Pressure) with 5 mL HNO3 and 1 mL HF (Romil UPA). The digestion temperature programme consisted of a ramp from room temperature to 100°C in 10 min, followed by a time sequence (5 min/step), allowing the maintenance and increase (
Water samples were also digested by microwave (8 min/slope from room temperature to 160°C and 10 min at 160°C). Each vessel contained 2 mL HNO3 and 18 mL of the deposition sample. All manipulations were conducted in a clean room equipped with a laminar flow bench.
The accuracy and precision of the method were controlled using the standard reference material (Urban Particulate Matter NIST1684). LOD was calculated for each element from the average value of the blanks, plus three standards; the detailed calculation of the relative error was reported in a previous paper [
Inorganic elements in the depositions samples were measured by Inductively Coupled Plasma-Quadrupole Mass Spectrometry (ICP-QMS Agilent 7500I). The inorganic elements analysed in this study are as follows: As, Cd, Co, Cr, Cu, Fe, Mo, Ni, Pb, Sb, Tl, V, and Zn. Determination of iron, copper, and zinc was carried out only on samples collected after 2007.
The data obtained were statistically analysed using the PCA (Principal Component Analysis) contained in the package STATISTICA 6.0 (StatSoft, Inc., 2001, Tulsa, OK, USA). We applied an autoscaling procedure on all the continuous variables, namely, the precipitation measured in mm of water, and the fluxes of the majority of elements and organic compounds. The analytes whose samples were often under detection limit were excluded from our statistical analysis.
Our first analysis regarded the contribution of the MOSE construction activities to the atmospheric depositions at the Lido inlet. This contribution was studied through a chemical analysis of depositions simultaneously collected in four different deposimeters (D1, D2, D3, and D4), placed at different distances from the construction site, from January 2005 to May 2006.
Figures
Average depositions of inorganic micropollutants for deposimeters D1, D2, D3, and D4 from January 2005 to May 2006.
Average depositions of organic micropollutants for deposimeters D1, D2, D3, and D4 from January 2005 to May 2006.
Rossini et al. [
Daily fluxes of inorganic elements (
As | Cd | Cr | Cu | Fe | Ni | Pb | Sb | V | Zn |
|
||
---|---|---|---|---|---|---|---|---|---|---|---|---|
D1 | Average | 1.2 | 0.3 | 3.7 | 3.6 | 5.8 | 0.6 | 4.7 | 676 | |||
Std. dev. | 0.6 | 0.4 | 1.7 | 1.6 | 2.8 | 0.2 | 2.0 | 788 | ||||
Min. | 0.3 | 0.0 | 1.1 | 1.0 | 2.9 | 0.3 | 1.9 | 26 | ||||
Max. | 2.4 | 1.5 | 6.5 | 6.1 | 13.1 | 1.2 | 8.5 | 2904 | ||||
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D4 | Average | 3.1 | 0.4 | 1.9 | 15.9 | 1792 | 1.9 | 6.1 | 1.7 | 5.1 | 39.4 | 296 |
Std. dev. | 9.0 | 0.8 | 1.1 | 22.9 | 3127 | 1.4 | 10.6 | 3.3 | 8.4 | 66.1 | 273 | |
Min. | 0.2 | 0.0 | 0.0 | 2.4 | 27 | 0.0 | 0.1 | 0.3 | 1.0 | 6.3 | 22 | |
Max. | 52.4 | 4.4 | 4.2 | 98.7 | 12890 | 6.7 | 59.8 | 15.1 | 44.0 | 277.2 | 1280 | |
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D5 | Average | 3.1 | 0.5 | 4.5 | 15.6 | 2726 | 4.4 | 8.8 | 2.3 | 9.6 | 48.5 | 464 |
Std. dev. | 3.1 | 1.0 | 4.9 | 25.3 | 3615 | 5.2 | 10.5 | 3.9 | 12.4 | 57.9 | 526 | |
Min. | 0.5 | 0.1 | 0.1 | 1.1 | 128 | 0.4 | 0.1 | 0.1 | 2.2 | 8.6 | 19 | |
Max. | 10.9 | 4.4 | 14.5 | 98.7 | 12890 | 9.2 | 59.8 | 15.1 | 44.0 | 277.2 | 1837 | |
|
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D6 | Average | 2.6 | 0.2 | 8.9 | 7.5 | 2672 | 4.7 | 9.9 | 4.9 | 8.6 | 125.7 | 279 |
Std. dev. | 2.5 | 0.5 | 7.7 | 7.5 | 3302 | 4.6 | 12.7 | 13.6 | 8.7 | 355.3 | 222 | |
Min. | 0.1 | 0.0 | 0.1 | 0.4 | 98 | 0.1 | 0.2 | 0.1 | 0.3 | 2.3 | 21 | |
Max. | 9.4 | 2.1 | 24.7 | 25.5 | 11831 | 14.6 | 46.4 | 57.5 | 29.8 | 1194.6 | 796 | |
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A [ |
Average | 0.001 | 0.7 | 4.4 | 14.3 | 622 | 6.4 | 14.2 | 0.2 | 5.7 | 97.6 | 842 |
Std. dev. | 0.4 | 0.9 | 1.6 | 6.4 | 386 | 2.4 | 4.5 | 0.2 | 2.2 | 59.8 | 518 | |
Min. | 0.4 | 0.2 | 2.2 | 6.6 | 203 | 3 | 8.2 | 0.0 | 2.7 | 25.5 | 288 | |
Max. | 1.9 | 3.5 | 7.8 | 29.3 | 1452 | 11.5 | 23.2 | 0.6 | 8.8 | 253.4 | 2035 | |
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B [ |
Average | 0.6 | 0.2 | 1.7 | 8.8 | 361 | 2.8 | 5.8 | 0.1 | 4.1 | 54 | 271 |
Std. dev. | 0.3 | 0.1 | 0.8 | 4.9 | 198 | 1.1 | 3.8 | 0.1 | 1.6 | 32.7 | 211 | |
Min. | 0.2 | 0.0 | 0.6 | 4.4 | 138 | 1.4 | 2.4 | 0.01 | 2.1 | 9.5 | 18 | |
Max. | 1.3 | 0.5 | 3.5 | 18.8 | 829 | 5.2 | 13.5 | 0.3 | 7.4 | 118.5 | 633 | |
|
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C [ |
Average | 0.6 | 0.4 | 3.0 | 10.1 | 536 | 4.5 | 11 | 0.2 | 6 | 69.3 | 286 |
Std. dev. | 0.2 | 0.5 | 1.2 | 4.7 | 303 | 1.8 | 3.5 | 0.2 | 3.9 | 53.6 | 236 | |
Min. | 0.2 | 0.1 | 0.8 | 4.9 | 268 | 1.9 | 6.1 | 0.0 | 2.1 | 19 | 32 | |
Max. | 0.9 | 2.0 | 5.5 | 18.5 | 1275 | 8.1 | 19.2 | 0.6 | 15.9 | 212.4 | 659 | |
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D [ |
Average | 0.8 | 0.3 | 3.4 | 12.7 | 446 | 6.9 | 7.6 | 0.1 | 8 | 96.7 | 1029 |
Std. dev. | 0.3 | 0.5 | 2.3 | 11 | 272 | 2.4 | 3.9 | 0.2 | 2.8 | 71 | 844 | |
Min. | 0.4 | 0.1 | 0.4 | 6.1 | 85 | 3.2 | 1.9 | 0.01 | 3.9 | 19.2 | 77 | |
Max. | 1.4 | 2.0 | 6.5 | 47.5 | 849 | 11.9 | 14.2 | 0.4 | 12.5 | 250.5 | 3352 |
A: city of Venice; B: northern Lagoon; C: southern Lagoon; D: Porto Marghera.
The fluxes of pollutants determined in D4, expressed as
Fluxes of chromium, nickel, and cobalt and precipitations in D4 from August 2005 to March 2010.
Fluxes of vanadium, lead, and arsenic and precipitations in D4 from August 2005 to March 2010.
Fluxes of thallium and molybdenum and precipitations in D4 from August 2005 to March 2010.
Fluxes of cadmium and antimony and precipitations in D4 from August 2005 to March 2010.
Fluxes of total PAH and total PAH R.C. and precipitations in D4 from August 2005 to March 2010.
Fluxes of fluoranthene and benzo(a)pyrene and precipitations in D4 from August 2005 to March 2010.
Behaviours of chromium, nickel, and cobalt are almost dependent on precipitations, as can be seen in Figure
A seasonal trend is more evident, with higher concentrations measured during the autumnal months.
In October 2009, a peak was registered in the concentration of most of elements, as nickel, cobalt, (Figure
In the cases of arsenic, lead, and vanadium, the concentration measured in October 2009 is one order of magnitude higher than the average concentration of the whole temporal series.
We can also notice a light seasonal trend, with higher concentrations in the autumnal-winter months, for vanadium, lead, arsenic (Figure
At last, molybdenum and thallium show a temporal trend that seems to depend on both precipitations and seasons (Figure
As for organic compounds, the seasonal trend is clearly visible for the total PAH (Figure
None of these pollutants, whether inorganic or organic, present any long-term trend. The dataset shows neither an increase nor a decrease over the years. In order to better define the role of precipitations in the flux of pollutants, we compared their average flux under three different precipitation conditions: less than 40 mm of water, between 40 and 80 mm, and more than 80 mm.
The diagrams of the average flux for each pollutant in the three pluviometrical series are reported in Figures
Average depositions of inorganic micropollutants for deposimeters D4 grouped according to precipitations.
Average depositions of organic micropollutants for deposimeters D4 grouped according to precipitations. Total IPA concentrations are reported separately because of different scale.
We can notice that the average fluxes of the elements during abundant precipitations (green series) are significantly higher than those during lower precipitations, in particular for vanadium, arsenic, antimony, and lead: these peaks are due to specific events, as previously observed, that occurred during 2009. For other elements, such as chromium, cobalt, nickel, and cadmium, the trend is more regular, emphasizing the high correlations between their fluxes and the precipitation (Figure
For organic pollutants, except for fluoranthene, the highest concentrations were observed during precipitations of medium intensity, showing the low correlation with their fluxes and precipitations (Figure
To better understand the relation between these variables, we performed a PCA analysis on the matrix constituted by fluxes determined in the D4 site. As variables, we used the precipitations and the daily fluxes of inorganic (As, Cd, Co, Cr, Mo, Ni, Pb, Sb, and V) and organic compounds (Fluo,
The first component accounts for 41,66% of the total variance, the second for 20,93%, and the third for 12,39%: total variance measured in the first three principal components is equal to 75%. From the scores plot (Figure
Score plot of the two first principal components obtained by PCA analysis of fluxes determined in D4.
Loading plot 3D of the three first principal components obtained by PCA analysis of fluxes determined in D4.
In order to investigate the spatial difference between fluxes of contaminants, three different sites placed at the three inlets of the Venice Lagoon were simultaneously sampled from September 2006 to March 2009: the previously mentioned D4 site, next to the Lido inlet in the north of the Lagoon, the D5 site next to the Malamocco inlet in the middle-south of the Lagoon, and the D6 site placed next to the Chioggia inlet in the north of the Lagoon (Figure
Figures
Average depositions of inorganic micropollutants for deposimeters D4, D5, and D6 from September 2006 to March 2009. Iron concentrations are in mg·m−2·day−1. Zinc concentrations are reported separately because of different scale.
Average depositions of organic micropollutants for deposimeters D4, D5, and D6 from September 2006 to March 2009. Total IPA concentrations are reported separately because of different scale.
Average daily fluxes reported in the D4 site, which were placed in the northern Venice Lagoon, are lower than those in other sites for all the elements and organic pollutants analysed. The site next to the Malamocco inlet presents a higher flux not only of copper (
The D6 site next to the Chioggia inlet presents high fluxes of chromium (
Our D6 results were also compared to those reported by Rossini et al. [
As for PAHs, the fluxes determined in D6 are much lower than those observed in site C, but comparable to the data reported by Rossini et al. [
Fluxes of pollutants in the southern area of the Lagoon are comparable with the data reported in other studies [
In the D5 site, next to the Malamocco inlet, higher fluxes of organic pollutants were determined. This is most probably due to the use of fuel in powerboats, which circulate mainly in the central area of the Lagoon and especially in the city centre. The site with the lowest fluxes was the one located in the northern part of the Lagoon, as also found by Rossini et al. [
As inorganic elements are concerned, we try to make a comparison between fluxes of contaminants in the three sites of the Lagoon and results obtained by a study carried out in the same sites, from 2007 to 2010, related to the concentrations of pollutants in PM10 [
In Table
Concentrations (ng/m3) of elements in PM10 measured in the three sites [
P. Sabbioni | Chioggia | Malamocco | ||
---|---|---|---|---|
V | Average | 4.40 | 4.40 | 5.60 |
(min.–max.) | (0.3–15.3) | (0.3–15.7) | (0.1–18.1) | |
|
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Cr | Average | 5.20 | 4.00 | 3.80 |
(min.–max.) | (0.4–21.9) | (0.4–72.1) | (0.4–12.4) | |
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Fe | Average | 357.00 | 394.40 | 319.60 |
(min.–max.) | (24.3–1347.3) | (30.2–3317.4) | (13.0–941.3) | |
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Co | Average | 0.20 | 0.20 | |
(min.–max.) | (0.01–2.2) | (0.03–1.0) | ||
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Ni | Average | 3.90 | 3.50 | 4.60 |
(min.–max.) | (0.2–18.3) | (0.3–28.7) | (0.5–17.0) | |
|
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Cu | Average | 9.80 | 6.40 | 8.90 |
(min.–max.) | (0.5–43.2) | (0.5–30.8) | (0.2–28.8) | |
|
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Zn | Average | 57.40 | 33.00 | 43.00 |
(min.–max.) | (1.1–177.3) | (0.3–102.8) | (1.3–129.6) | |
|
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As | Average | 2.00 | 1.10 | 2.10 |
(min.–max.) | (0.1–13.3) | (0.1–6.1) | (0.1–13.9) | |
|
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Cd | Average | 2.20 | 1.50 | 2.70 |
(min.–max.) | (0.01–20.7) | (0.01–13.2) | (0.01–35.6) | |
|
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Sb | Average | 8.60 | 4.70 | 7.30 |
(min.–max.) | (0.6–35.9) | (0.1–53.7) | (0.2–34.5) | |
|
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Tl | Average | 0.06 | ||
(min.–max.) | (0.001–0.5) | |||
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Pb | Average | 21.30 | 16.10 | 21.20 |
(min.–max.) | (1.6–161.8) | (0.5–93.1) | (0.8–325.1) |
We performed a PCA statistical analysis on a matrix constituted by the fluxes of inorganic elements (As, Cd, Co, Cr, Mo, Ni, Pb, Sb, and V), organic compounds (
The first component accounts for 37,33% of the total variance, the second for 18,33%, and the third for 15,22%: total variance measured in the first three principal components is equal to 70,9%.
Table
Factor coordinates of the variables, based on correlation, of the first three factors obtained by PCA analysis of fluxes collected in D4, D5, and D6 from September 2006 to March 2009.
Variable | Factor 1 | Factor 2 | Factor 3 |
---|---|---|---|
V | 0.951* | 0.021 | 0.009 |
Cr | 0.528 | −0.685* | 0.249 |
Co | 0.416 | −0.799* | 0.290 |
Ni | 0.847* | −0.357 | 0.112 |
As | 0.741* | 0.341 | −0.157 |
Mo | 0.619* | 0.028 | −0.218 |
Cd | 0.694* | 0.584 | −0.166 |
Sb | 0.547* | 0.400 | −0.140 |
Pb | 0.583* | 0.214 | 0.066 |
|
0.110 | 0.444 | 0.840* |
|
−0.023 | 0.286 | 0.915* |
Prec. | 0.584* | −0.146 | −0.039 |
Score plot 3D of the three first principal components obtained by PCA analysis of fluxes collected in D4 (○), D5 (□), and D6 (△) from September 2006 to March 2009.
Samples collected in the D4 site (blue circles) are all grouped. The other two sites (red squares for Malamocco and green triangles for Chioggia) have many samples separated from the others because of Factor 1 (in particular V, Ni, As, and Cd,) and Factor 3 (organic compounds). The statistical analysis performed on the three sites confirms what emerged above, namely, that the D4 site presents the most regular fluxes, while the other sites are characterised by several peaks in the fluxes of pollutants.
The aim of the present work was investigating the spatial variability of depositions in the Venice Lagoon, its correlation with precipitations, and the possible impact of the construction of the MOSE dams, by studying the fluxes of inorganic and organic pollutants in the areas next to the construction sites. The contribution of the MOSE construction activities to the atmospheric depositions at the Lido inlet was studied through a chemical analysis of depositions simultaneously collected in four different deposimeters placed at different distances from the construction site, from January 2005 to May 2006. The fluxes measured in the inner area of the yard were comparable with fluxes found in the central Lagoon during other studies, while fluxes measured in deposimeters far from the yard were comparable with those found in remote areas of the Lagoon. The characterization of bulk depositions, with respect to inorganic elements and organic compounds, did not show evidence of any inverse correlation between element concentration and the distance from the construction site. The impact of construction activities on atmospheric depositions appears strictly limited to the construction area.
Pollutants had different temporal trends and a different correlation with the precipitations, as shown by temporal trends and statistical analysis via PCA. In particular, nickel, chromium, and cobalt had fluxes strictly influenced by precipitation; elements such as arsenic, lead, and vanadium showed behaviour partially connected with precipitations, mostly due to particular events with abundant precipitations. The temporal trend of other elements, such as antimony, cadmium, molybdenum, and thallium, did not show any evident correlation with precipitation or season, but rather behaviour influenced by multiple factors. Organic compounds showed, on the contrary, a seasonal temporal trend, with peaks occurring during late winter-early spring.
Moreover, for all pollutants here reported, both inorganic and organic, we cannot observe any long-term trend and neither an increase nor a decrease over the years has been put in evidence in the dataset.
The spatial distribution of contaminants’ fluxes highlighted that the area next to the Lido inlet (northern Lagoon) had lower and almost homogeneous fluxes of contaminants, while, in the other sites placed next to the Malamocco and Chioggia inlets, contaminants’ fluxes were more variable. The southern Lagoon showed traces of the influence of other sources, like the nearby city of Chioggia and the Po Valley. In the site close to the Malamocco inlet, higher fluxes of organic pollutants were determined. This is most probably due to the use of fuel in the powerboats, which circulate mainly in the central area of the Lagoon and especially in the city centre.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work was supported by the Ministero delle Infrastrutture e dei Trasporti Magistrato alle Acque di Venezia (Italian Ministry of Infrastructure and Transport, Venice Water Authority) through its dealer Consorzio Venezia Nuova. The authors wish to thank the Venice Water Authority for permission to use the data and CORILA (Consortium for Managing the Research Activities Concerning the Venice Lagoon System) for the valuable assistance and logistic support during the sampling campaigns. The authors would like to thank Daniela Almansi (Department of Environmental Sciences, Informatics and Statistics, Ca’ Foscari University, Venice, Italy) for the English revision of the paper.