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Evaluation of heavy metal pollution in the Venetian lagoon by using Mytilus galloprovincialis as biological indicator
The Science of the Total Environment, 119 (1992) 29-41 Elsevier Science Publishers B.V., Amsterdam
29
Evaluation of heavy metal pollution in the Venetian lagoon by using Mytilus galloprovincialis as biological indicator P. Zatta a, S. Gobbo a, P. Rocco a, M. Perazzolo b and M. Favarato b aCNR-Unit for the Study of Biochemistry and Physiology of Hemocyanin and other Metallo-Proteins, University of Padova, Via Trieste 75, 35131 Padova, Italy bDepartment of Biology, University of Padova, Via Trieste 75, 35131 Padova, Italy
ABSTRACT This study reports the analysis of heavy metal (Cd, Co, Cu, Cr, Hg, Fe, Mn, Ni, Pb, Zn) and As accumulated in the mollusc Mytilus galloprovincialis collected in the Venetian lagoon between March and September 1988. This environmental biomonitoring project was carried out using natural population of the molluscsattached to the 'Briccole', which limit the navigation canals into the lagoon. These data were compared with those reported by other authors in analogous studies ~ubtished about a decade ago. A small improvementon the heavy metal pollution of the Ven~etianlagoon can be deduced from this comparison, presumablydepicting a positive signal of a new downward trend in metal concentrations. Continuous monitoring of the fragile lagoonal ecosystemmust be an important commitmentdue to the economic and historical importance of the Venetian lagoon.
Key words: Venetian lagoon; biological indicators; biological monitoring; heavy metals; ecotoxicology; Mytilus
INTRODUCTION The Venetian lagoon is located at the north of the Adriatic Sea. It is situated between the m o u t h o f the Rivers Brenta and Bacchiglione in the south and the River Sile in the north. It extends about 12 km with a total surface area o f about 546 km 2. The average depth is about 500 cm. The lagoon connects with the Adriatic Sea through three port entrances: Lido, Malamocco and Chioggia, and it can be divided into three basins. The first basin in the north part o f the lagoon has an area of 270 km 2 within which the city o f Venice is located. The second basin in the central part of the lagoon has an area of 160 km 2 and includes part of the industrial area of Port Marghera. The third basin is in the south part of the lagoon with a surface area o f 116 km 2 and includes the city o f Chioggia. 0048-9697/92/$05.00
© 1992 Elsevier Science Publishers B.V. All rights reserved
30
P. ZATTA ET AL.
The rivers and artificial canals that flow into the lagoon (Meneghin and Zamperoni, 1982) are the major contributors of the industrial, urban, and agricultural pollution found there. They carry the run-off from the reclamation and irrigation of the surrounding agricultural area. The construction of the industrial area of Port Marghera, the large-scale urban development of the Venice hinterland, and the massive utilization of chemicals in agriculture are the major reasons for the changing and worsening environmental conditions of the very fragile lagoonal ecosystem. Studies of the accumulation and distribution of trace elements in the Venetian lagoon have been done: Perin (1975) and Studio Tecneco (1978) analyzed the water, Giordani-Soika and Perin (1974) examined the sediments, while Barbaro et al. (1978), Moretti et al. (1979) and Campesan et al. (1980) used living organisms. The utilization of living organisms as the marine, and in more general way as the aquatic indicator of environmental pollution is now a well established technique (Goldberg, 1975) recognized by the International Monitoring Programs (IWM, 1980). In spite of the limitation of this approach due to the effects of variability of the physiological conditions of the aquatic medium on the living organisms (Morris, 1974; Phillips, 1976; Cossa et al., 1980), results achieved with this approach are of great interest in the evaluation of the water quality and consequently in detecting the degradation of the aquatic environment. Metal ions can occur in the aquatic environment under different forms (Fig. 1). The toxicity of a metal or of its compound in a biological system, depends upon different factors: (1) metal dose; (2) intrinsic toxicity; (3) binding capacity of the metal per se; (4) specificity of the biological system to
ORGANIC HYDROUTICALLY UNSTABLE COMPLEXES
ORGANIC STABLE ~. COMPLEXES
•
f
n+ Me
PARTICULATE
~OIDS
SEDIMENTS INORGANICCOMPLEXES
Fig. 1. Multiforms in which metal ions appear in aquatic environment.
EVALUATION OF HEAVY METAL POLLUTION IN THE VENETIAN LAGOON
31
transport of metal through a target organ; (5) biotransformation of a metal into a derivative and sometimes more toxic forms; and (6) ability of the living organism to sequester or secrete the metal, etc. Metal can otherwise modify the permeability of the cellular and subcellular membrane, the structure and function of proteins and nucleic acids, the metabolism of neuromodulators and hormones with a consequent influence on the homeostatic phenomena. The solubility of certain metals or of their compounds in water or in lipidic environment can influence their own accumulation in a biological system and consequently their toxic effect. The interaction of a toxic metal with a biological system is almost always complex. All these aspects must be kept in mind when living organisms are utilized as biological indicators of pollution. Biological monitors seem to be very useful tools due to the fact that the accumulation of heavy metals in aquatic organism is sometimes 103-106times higher with respect to the aquatic environment where the animals are sampled (Phillips, 1976). According to some authors (Haug et al., 1974) an ideal biological indicator of trace elements must have a sedentary or sessile existence, be abundant in the area of study and have relative longevity. Ease of sampling, tolerance to brackish water and the ability of accumulating pollutants with a high concentration factor are also important. There should be a strong correlation between metal accumulation and the metal concentration in the surrounding water. Mytilus species satisfies each of these conditions well. In this study, the mollusc Mytilus galloprovincialis has been utilized as a biomonitor of heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Hg, Pb, Zn) and non-metal (As) in the Venetian lagoon during some scientific cruises carried out in March, June and September 1988. As far as we know, this is the most complete study of the metal pollution in the Venetian lagoon carried out utilizing marine organisms as biological indicators. EXPERIMENTAL
Mytilus galloprovincialis was collected from 44 stations in March, June and September 1988, utilizing samples of 3-5 cm from natural population attached to the 'Briccole' that limit canals of lagoonal navigation. Sampling sites are indicated in Fig. 2 and correspond to the number in brackets in Table 1. All 'Briccole' carry a number which corresponds to our sampling sites, and is reported in Table 1 at the right of the location name. Once collected, samples were kept at 4°C during the time of transferring to the laboratory. All mussels were sampled according to the procedure described by Phillips (1976). About 10 individuals per station were collected each time. The shell was removed and the soft tissues digested in a mixture of HNO3/H2SO4
32
P. Z A T T A ET AL.
\ N
.jo:
./
\
/
!
.PORT. ENTRANCE LIDO
ADRIATIC
SEA
MALAMOCCO
NCE CHIOGGIA
i,:'i~:ii!:!
Fig. 2. Study area: numbers correspond to the sampling stations.
33
EVALUATION OF HEAVY METAL POLLUTION IN THE VENETIAN LAGOON
TABLE 1 The first numerical line reports the accumulation of metal ions and As in Mytilus galloprovincialis (#g/g of fresh wt) collected in different sampling stations [#] of the Venetian lagoon. The second numerical line represents the S.D. The number on the right of the sampling location represents the number marked on the 'Briccolas' which delimit the navigation canals As
Cd
Co
North basin [30] Cimitero 7 2,203 0.264 0.195 0.164 0.034 0.044
Cu
Cr
2.024 0,215
-
[31] Light of Murano Island 49 2.218 0.223 0.113 1.94 0.680 0.085 0.073 1.046
Fe
Hg
Mn
Ni
Pb
Zn
46.80 20.04
0.079 0.014
2.127 0.592
0.182 0.063
0.300 0.091
27.34 11.45
63.76 28.99
0.083 0.014
2.430 0.685
0.446 0.085
0.351 0.095
26.49 10.39
46.92 29.08
0.073 0.016
8.30 2.84
0.300 0.106
0.212 0.121
37.32 10.13
50.39 18.19
0.178 0.007
2,090 0,417
0.322 0.164
0.222 0.040
23.78 9.86
60.97 23.55
0.137 0.036
38,480 19.77
0.437 0.204
0.316 0.082
19.12 3.25
[32] S. Giacomo in Palude Island 3 2.272 0.625
0.300 0.203
0.197 0,088
1.60 0.72
-
[33]Madonna delMonte Island 26 2.353 0.186 0.178 1.872 0.20 0,124 0.108 0 . 0 8 1 0.521 0.08
[34]Mazzorbo Island 5 1.757 0.196 0.291 0.083
0.318 0.150
2.033 0.311 1.449 0.154
0,172 0.077
2.085 0,929
0.368 131.37 0 . 1 6 1 10.17
0.132 0.053
5.323 3.555
0.516 0.170
0.379 0.011
15.76 1.57
[36] Torcello Island 7 2.202 0.207 0.295 0.287 0.094 0.033
2.069 0.360
0,317 0.231
97.72 42.96
0.123 0.041
4.324 0.271
0.578 0.518 0 , 2 1 1 0.161
14.43 1.48
[37] Torcello Island 6 2.313 0.127 0.210 0.221 0.079 0.041
1,909 0.341
0.239 0.048
63,38 21.83
0,136 0,030
3 . 1 4 1 0,549 0.624 0.078
1.449 0.509 0.136 0.249
167,53 27,62
0,041 0,016
35.718 11.004
1.783 0.280 0.924 0.176
149.67 2.36
0,049 0.020
5.205 2.487
[35] Silone 35 1.615 0,196 0.520 0 . 0 8 1
0.212 0.121
14.97 2.07
0.530 0.128
0.246 0.041
24.96 2.12
0.300 0.106
0.299 0.100
16.23 6.77
[38] Canal of Burano Island 9 1.815 0.083 0.806 0.085
0,273 0.045
[39] Burano Island 10 1.877 0.151 0.806 0.072
0.248 0,002
34
P. ZA'I'fA ET AL
TABLE 1 As
(Continued)
Cd
Co
Cu
Cr
Fe
Hg
Mn
Ni
Pb
Zn
[40] Canal of Burano Island 15 1.552 0 . 0 5 1 0.438 0.048
0.082 0.032
1.082 0 . 4 1 1 107.64 0.624 0.374 51.26
0.130 0.020
5 . 0 1 1 0.334 1 . 4 7 1 0.127
0.351 0.095
15.83 7.97
1 . 4 9 9 0.213 0.060 0.075
98.98 11.44
0.133 0.009
4.700 2.492
0.513 0.079
0.519 0.207
23.75 7.62
[42] S. Francesco delDeserto Island 1.808 0.266 0.220 1.576 0.519 0.232 0.057 0.085 0.430 0.329
68.42 1.24
0.156 0.036
4.486 0.413 1 . 3 3 8 0.147
0.416 0.306
19.25 3.51
55.35 6.10
0.051 0.040
3.566 1.534
0.280 0.067
0.150 0.007
21.23 3.80
138.26 34.41
0.162 0.009
6.156 0.449 1 . 0 3 6 0.081
0.222 0.040
24.94 5.86
44.719 0.161 11.687 0.181
7.105 2.145
0.460 0.049
0.616 0.487
19.754 8.048
0.229 0.030
46.668 14.671
-
2.082 0.219
0.092 0.003
0.455 0.184
10.619 4.626
1.242 0.197 0.228 0.058
56.261 10.000
-
3.108 0.518
0.359 0.025
0.468 0.153
23.670 4.457
1.227 0.246 0.272 0.093
59.672 16.070
-
4.209 0.286
0.258 0.500 0 .0 1 1 0.016
27.687 6.972
1.759 0.274 0.948 0.146
68.543 9.601
0.043 0.003
3.992 0.757
0.392 0.177
0.526 0.126
18.881 1.882
1.846 0.183
59.508 9.878
-
2.381 0.772
0.268 0.084
0.445 0.123
20.368 4.885
[41]Gravan 72 2.592 1 . 6 3 6 0.101 0.490 0.014 0.103
[43] Sabbioni Point 43 2.284 0.650
0.165 0.081
0.151 0.035
1 . 2 3 0 0.107 0.294 0.005
[44] Certosa Island 4 2.216 0.560
0.169 0.044
0.310 0.095
1.586 0.254
0.585 0.050
[1] S. Servolo Island 5 1.477 0.146 0.365 2.530 0.448 0.0930 0 . 2 4 1 1.606
0.500 0.234
Cen~albasin
[2] S. Maria delleGrazie Island 12 0.940 0.319
0.190 0.115
0.321 0.282
0.723 0.117
[3] Sacca Sessola Island 8A 0.290 0.099
0.196 0.072
0.233 0.016
[4] S. Clemente Island 144 1.362 0.254 0.275 0.120
0.242 0.055
[5] S. Spirito Island 135 1.422 0.220 1.265 0.072
0.126 0.089
[6] Poveglia Island 78 0.902 0.070 0.130 0.142 0.018 0.004
0.154 0.024
35
EVALUATION OF HEAVY METAL POLLUTION IN THE VENETIAN LAGOON
TABLE 1 As
(Continued)
Cd
Co
Cu
Cr
Fe
Hg
[7]Malamocco 70 1.360 0.387 0.369 0.259 0.032 0.010
1.692 0.540
0.348 0.094
89.050 23.997
0.074 0.020
[8]Alberoni 31 1.315 0.197 0.263 0.350 0.094 0.025
1.061 0.091 0.361 0.009
59.638 16.320
Pb
Zn
5 . 5 2 1 0.687 2.069 0.062
0.661 0.221
12.656 1.561
0.064 0.017
4.411 0.603 1 . 3 0 8 0.412
0.850 0.257
18.236 5.574
0.017 0.005
3.186 0.096 1 . 2 5 2 0.029
0.261 0.014
16.295 2.602
-
2.303 0.953
0.602 0.118
17.095 2.638
2.852 0.773 1 . 0 1 2 0.215
0.691 0.214
14.934 1.997
0.556 0.087
16.088 2.284
[9]Alberoni Lighthouse 10 1.959 0.084 0.215 0.665 0.350 0.017 0.135 0.082
0.131 0.017
34.528 18.226
[10]Malamocco 16 1.525 0.066 0.192 0.122 0.004 0.012
0.926 0.236
0.204 0.021
108.374 56.944
[11] S. Leonardo Canal 232 1.089 0.242 0.120 0.012 0.193 0.188 0.051 0.339
0.296 0.023
103.187 0.045 1.936 0.018
Mn
Ni
0.388 0.134
[12] Lussario Canal 163 0.897 0.153 0.227 1.410 0 . 1 8 1 0.247 0.007 0.043 0.505 0.025
58.666 0.032 1 2 . 2 5 5 0.023
2.790 0.980
[13] Fusina 12 0.997 0.387 0.217 0.643 0.129 0.023
1.116 0.238 0.305 0.072
48.854 1.629
0.036 0.002
3 . 4 6 1 0.692 0.665 i.289 0.251 0.358
23.375 7.482
0.165 0.108
0.058 0.304
0.468 0.051
34.510 0.614
0.069 0.012
6.229 3.365
0.575 0.456
0.983 0.045
28.224 1.847
[15] Trezze Island 9 1.025 0.323 0.312 0.326 0.015 0.076
0.970 0.167
0.157 0.025
75.945 2.730
-
4.419 0.608
0.474 0.018
0.658 0.074
30.103 11.921
[16] S. Angelo delle Polverari Island 36 0.841 0.350 0.204 0.669 0.144 44.678 0.198 0.168 0.060 0.082 0.041 12.432
0.029 0.007
4.672 0.198 1 . 8 8 5 0.100
0.329 0.151
28.37 14.662
[17] Giudecca Island 3 0.816 0.135 0.255 1.755 0.196 0.115 0.026 0 . 0 1 1 0.650 0.054
0.033 0.001
6.247 1.30
0.33 0.110
[14] Port Marghera 68 1.110 0.734 0.460 0.072
43.241 5.330
0.240 0.435 0 . 1 0 1 0.081
17.022 4.192
36
P. ZATTA ET AL,
TABLE 1 As
(Continued)
Cd
Co
Cu
Cr
Fe
Hg
Mn
Ni
Pb
Zn
0.241 0.015
1.181 0.450
32.378 11.180
0.171 0.164
15.243 6.293
[18] S. GiorgioMaggiore Island 11 1.652 0.212
0.259 0.083
100.867 22.467
-
5.350 2.491
South lmsin [19] S. Pietro In V o l t a 2 3 1.271 0.047 0.288 0.029
0.529 0.195
1.939 1.100
-
1.256 0.213
0.121 0.043
0.763 0.087
18.057 3.263
-
2.498 0.050
0.101 0.039
0.219 0.092
18.542 4.581
-
0.169 0.119
0.991 0.195
2.323 0.410
-
3.490 1.894
-
0.364 0.094
17.060 5.490
-
0.173 0.080
0.822 0.168
23.997 15.582
-
2.333 0.082
0.123 0.050
0.422 0.092
15.153 3.012
[23] L o m b a r d o Canal 22 1.122 0.094 0.256 0.050
0.888 0.470
20.537 6.149
-
2.055 0.569
-
0.135 0.078
12.633 2.090
-
6.814 2.618
-
0.212 0.117
16.453 1.697
0.517 0.181
0.142 0.007
0.288 0.014
[20] S. Pietro di Pellestrina 70 1.159 0.063
0.052 0.007
-
[21]Pellestrina 138 1.337 0.504
0.058 0.004
[22] Caroman 21 1.063 0.124
0.028 0.016
[24] SS Romea 40 1.265 0.389
0.154 0.043
-
0.204 0.114
1.201 0.832
ND
[25] L o m b a r d o Canal 70 1.921 0.007 0.087 0.126 0.001 0.009
0.771 0.278
29.252 22.024
-
2.443 1.118
-
0.225 0.063
11.564 2.066
0.706 0.127
50.831 36.595
-
2.149 0.814
0.154 0.079
0.272 0.040
14.258 4.238
0.129 0.085
0.629 0.254
35.22 4.25
0.022 0.005
1.856 1.068
0.070 0.045
0.295 0.048
17.163 3.753
[28] Valgrande Canal 22 0.688 0.039 0.109 0.087 0.005 0.073
0.588 0.071
0.019 0.002
1.484 0.598
-
0.228 0.060
8.018 2.351
[26] Perognola Canal 248 0.960 0.184
0.019 0.009
0.044 0.002
0.195 0.103
[27] Perognola Canal 186 1.373 0.200
0.049 0.025
-
ND
37
EVALUATION OF HEAVY METAL POLLUTION IN THE VENETIAN LAGOON
TABLE 1 As
Cd
(Continued) Co
Cu
Cr
0.160 0.104
0.429 0.119
Fe
Hg
Mn
Ni
Pb
-
0.353 0.028
Zn
[29] Canale N u o v o 76 24.877 2.833
-
3.666 1.446
7.095 0.425
- , below detection limit. ND, not determined.
(Suprapur Merck) (5:1 v/v) at room temperature for 48 h, then heated at 70°C in reflux to complete the digestion. The digestion solution was diluted to a known volume and filtered through a 0.40/~m membrane. Metal determination was carried out by means of an atomic absorption spectrophotometer (Perkin-Elmer 4000), following the instrumental guidelines provided by the manufacturer. All analytical procedures were carried out according to the International Mussel Watch procedure (1980). Statistical analyses of the variance was done using the methods of Romeril (1971) and Phillips (1976). Other statistical analyses were carried out according to Johnel et al. (1967). RESULTS AND DISCUSSION
Bernardi et al. (1986) reported that every year about 414 tonnes of iron, 4 tonnes of nickel, 5.5 tonnes of copper, and 4.5 tonnes of lead are discharged into the Venetian lagoon. The total content of the heavy metals in the water consists of the soluble fraction and the fraction absorbed into the suspended particles (Fig. 1). Most of the metals introduced into the lagoon precipitate out as insoluble compounds since the water pH is alkaline, and consequently are deposited in the sediments. It has been observed that high metal concentrations of effluents coincide with the period of major water flow in the rivers which occurs between May and June and late autumn. Data reported here represent the average of the three sampling cruises. Results are expressed in /~g/g of fresh tissue. Table 1 shows the concentration of each metal in mussels collected from the different stations and grouped in each of the three basins A rsenic The most important industrial sources of As are the founderies and glass factories. In agriculture As is used in certain pesticides. We found a relatively high concentration of As in M. galloprovincialis in the north part of the
38
P. ZATTA ET AL.
lagoon (1.5-2.4 ppm) and lower concentrations in the central part of the lagoon (1.1-2.0 ppm) and in the south basin (1.0-1.5 ppm).
Cadmium Cadmium is released both from industrial and domestic waste. Industries with a potential output of cadmium are those involved in the production of non-ferrous metals. Bernardi et al. (1986) reported a high concentration of Cd in several effluents of the Venetian lagoon: 111 ppb in the Dese River, 206-330 ppb in the Osellino Canal, 130 ppb in the Trezze Canal with the highest concentration of 1096 ppb detected in the Naviglio-Brenta Canal. Values in our sampling are higher in the mussels collected in the central lagoon (0.2-0.7 ppm), lower in the north basin (0.05-0.3 ppm) and lowest in the south part (< 0.05 ppm). Our values are lower than the respective average values of 0.4 and 2.3 ppm reported a few years ago by Moretti et al. (1979) and Campesan et al. (1980).
Cobalt Seventy-five percent of the consumption of Co goes to the production of steel and alloys in the Veneto Region, and a marginal quantity is used in the fertilizers since low Co concentration in soil may induce Co deficiency among cattle. While the concentration of this metal is at the limit of instrumental detection in our samples from the southern part of the lagoon, in the north and central basins, values between 0.1 and 0.3 ppm were measured.
Copper The vast majority of copper is utilized by electrical industries of generators, telephones, electric power lines etc. The presence of Cu in our sampling ranges from 0.8 ppm in the south lagoon to 2.4 ppm as a higher concentration in the north lagoon (stations 30-37).
Chromium The presence of this metal in the environment is due exclusively to industrial production. It is worth noting that this chromium is utilized in the tanning industries located in the Vicenza area, a few kilometers from Venice, in numerous small and medium size industries in the Veneto Region and in the industrial area of Port Marghera. Values of chromium reported by other authors in M. galloprovincialis (Campesan et al., 1980) are in the order of 0.3-0.4 ppm, similar to our determinations in the central and south lagoon; higher values (0.6 ppm) were measured in the north basin.
EVALUATION OF HEAVY METAL POLLUTION IN THE VENETIAN LAGOON
39
Mercury Moretti et al. (1979) reported that fish from the Mediterranean sea contain high concentrations of Hg which is caused by a contribution of this metal to the sea from the mining area of Tuscany in the north-central part of Italy and Alpi Giulie in the north-western part of Italy close to the Yugoslavian border (Majori et al., 1973). Our values on Hg are between 0.05 and 0.18 ppm in the south lagoon and lower values were measured in the central basin (0.05 ppm) and, by limited instrumental detection, in the major number of our sampling stations. Values of Hg in the lagoonal effluents (Bernardi et al., 1986) show a higher concentration equal to 2120 ppb in the Osellino Canal, and 321.9 ppb in the Taglio Nuovissimo. These data, as specified by those authors, are due to occasional discharge or mixing of the sediments and do not represent a constant value of pollution.
Manganese Manganese compounds are used in steel alloys, in oxidizing-agent production, in the manufacture of dry batteries, electrical apparatus, ceramics, glass, fertilizers, and animal food additives. Almost all these activities are present in areas surrounding Venice and, consequently, they can be a potential hazard as sources of pollution. Manganese in our samples is between 2 and 6 ppm in the animals collected in the central lagoon, 1.5-4.0 ppm in those collected in the south lagoon and 5.0 ppm in those from the north basin. Average values reported by other authors correspond to our determinations (Campesan et al., 1980).
Nickel Our data on Ni accumulation in M. galloprovincialis give concentrations between 0.2 and 0.8 ppm in the north-central part of the lagoon and lower values in the south and central basin.
Iron In our analysis we found values of Fe accumulation in mussels ranging between 50 and 150 ppm in the north part of the lagoon, 50-100 ppm in the central basin and lower levels in the south lagoon.
Lead The development of industrialization and motorization is coincident with the increase of Pb pollution of the Venetian lagoon. The highest concentra-
40
P. ZATTA ET AL.
tion in the water was reported by Bernardi et al~ (1986) in the Osellino Canal in the range of 30-40 ppb. Concentration of Pb in the sediments was reported to be between four and eight times higher with respect to the average values, in the area of S. Angelo delle Polveri area, which corresponds to our sampling station No. 16 and in good agreement with our values of accumulation in M. galloprovincialis. Our determinations of Pb in the mussels used as biomonitor, range from 0.2 to 0.5 ppm in the north part of the lagoon, 0.4-1.1 ppm in the central basin and the lowest concentration was found in the south lagoon. Our data are lower than those reported by other authors (Campesan et al., 1980).
Zinc Zinc is utilized in the production of light alloys, rubber industries, paints and in some products for agriculture. Moretti et al. (1979) reported values of Zn in M. galloprovincialis at least double with respect to our findings. CONCLUSIONS
The industrial and economic structure of the Veneto Region is characterized by an enormous development and concentration of small and medium size industries which have created some difficulty in controlling the environmental pollution. The Venetian lagoon is a fragile ecosystem with particular characteristics heavily impacted by the Port Marghera, one of the largest industrial areas in Europe, and by the city of Venice. The lagoon is the final part of a drainage basin which carries waste from farming and agricultural activities. In view of the importance of the Venetian lagoon, both from the economic and from the historical standpoints, we carried out this study of biomonitoring and analyzing the accumulation of As and the heavy metal ions in
Mytilus galloprovincialis. Data of highest accumulation were found in the north part of the lagoon and the lowest values concern the south basin. This seems reasonable with the geographical position of rivers and canals and the consequent introduction of pollutants. ACKNOWLEDGEMENTS
Authors acknowledge Mr. Benito Bonora of the Istituto di Biologia del Mare, Venice, of the National Research Council of Italy, for the technical support during the sampling and the ECOLAB laboratory, Padova, Italy for the analysis of arsenic and lead.
EVALUATION OF HEAVY METAL POLLUTION IN THE VENETIAN LAGOON
41
REFERENCES Barbaro, A.A., A. Francescon, B. Polo and M. Bilio, 1978. Balanus amphitrite (cirripeathoracica), A potential indicator of fluoride, copper, lead, chromium and mercury in North Adriatic lagoon. Mar. Biol., 46: 247-257. Bernardi, S., R. Cecchi, F. Costa, G. Germandi and S. Vazzoler, 1986. Trasferimenti di acqua dolce e di inquinanti nella laguna di Venezia. Inquinamento, 1: 46-64. Campesan, G., R. Capelli, G. Pagotto, G. Stocco and G. Zanicchi, 1980. Heavy metals in organisms from the Lagoon of Venice, Italy, 5 journee' Etud. Pollutions, Cagliari, C.I.E.S.M., 6: 179-185. Cossa, D., E. Bourget, D. Pouliot, J. Piuze and J.P. Canut, 1980. Geographical seasonal variations in the relationship between trace metal content and body weight in Mytilus edulis. Mar. Biol., 58: 7-14. Giordani-Soika, A. and G. Perin, 1974. L'inquinamento della laguna di Venezia: studio sulle modificazioni chimiche e del popolamento sottobasale dei sedimenti lagunari negli ultimi vent'anni. Boll. Museo Civico Storia naturalew, 26: 25-68. Goldberg, E.D., 1975. The mussels watch: a first step in global marine monitoring. Mar. Poll. Bull., 6:111. Haug, A.S., S. Melson and S. Omag, 1974 . Estimation of heavy metal pollution in two Norwegian t]ord areas by analysis of the brown alga Ascophyllum nodosum. Environ. Pollut., 7: 173-193. International Mussel Watch, 1980. National Academy of Sciences, USA, Washington DC, pp. 78-132. Johnels, A.G., T. Westmark, W. Berg, P.I Person and B. Sjorstrand, 1967. Pike (Osox lucius L.) as indicator of mercury contamination in environment. Oikos, 18: 323-333. Majori, L. and F. Petronio, 1973. Su una metodologia semplificata del dosaggio del mercurio nei tessuti biologici. Igiene Moderna, Gennaio-Febbraio. Meneghin, M. and G. Zamperoni, 1982. Morfologia dei corpi idrici sversanti nella laguna di Venezia. ISDGM-CNR, Tech. Rep. 117, Venezia. Moretti, G., L. Zuzzi and G.M. Pellizzato, 1979. L'inquinamento marino e lagunare. 1. I metalli pesanti. Lav. Soc. Ven. Sci. Nat., 4: 6-19. Morris, A.W., 1974. Seasonal variations of dissolved metals in inshore waters of Menai Straits. Mar. Poll. Bull., 5: 54-59. Perin, G., 1975. L'inquinamento chimico della laguna di Venezia. In: Problemi dell'inquinamenti lagunare. Cons, Depurazione Acque della Zona Industriale di Porto Marghera, Venezia, pp. 47-89. Phillips, D.J.H., 1976. The common mussel Mytilus edulis as an indicator of pollution of zinc, cadmium, lead and copper. I. Effect of environmental variables on uptake of metals. Mar. Biol., 38: 59-69. Romeril, M.G., 1971. The uptake and distribution of Zn 65 in oysters. Mar. Biol., 9: 347-354. Studio TECNECO, 1978. Valutazione dei limiti di accettabilita' delle sostanze inquinanti agli scarichi versati in laguna. Definizione di un sistema di controllo delle acque lagunari. Comune di Venezia.
29
Evaluation of heavy metal pollution in the Venetian lagoon by using Mytilus galloprovincialis as biological indicator P. Zatta a, S. Gobbo a, P. Rocco a, M. Perazzolo b and M. Favarato b aCNR-Unit for the Study of Biochemistry and Physiology of Hemocyanin and other Metallo-Proteins, University of Padova, Via Trieste 75, 35131 Padova, Italy bDepartment of Biology, University of Padova, Via Trieste 75, 35131 Padova, Italy
ABSTRACT This study reports the analysis of heavy metal (Cd, Co, Cu, Cr, Hg, Fe, Mn, Ni, Pb, Zn) and As accumulated in the mollusc Mytilus galloprovincialis collected in the Venetian lagoon between March and September 1988. This environmental biomonitoring project was carried out using natural population of the molluscsattached to the 'Briccole', which limit the navigation canals into the lagoon. These data were compared with those reported by other authors in analogous studies ~ubtished about a decade ago. A small improvementon the heavy metal pollution of the Ven~etianlagoon can be deduced from this comparison, presumablydepicting a positive signal of a new downward trend in metal concentrations. Continuous monitoring of the fragile lagoonal ecosystemmust be an important commitmentdue to the economic and historical importance of the Venetian lagoon.
Key words: Venetian lagoon; biological indicators; biological monitoring; heavy metals; ecotoxicology; Mytilus
INTRODUCTION The Venetian lagoon is located at the north of the Adriatic Sea. It is situated between the m o u t h o f the Rivers Brenta and Bacchiglione in the south and the River Sile in the north. It extends about 12 km with a total surface area o f about 546 km 2. The average depth is about 500 cm. The lagoon connects with the Adriatic Sea through three port entrances: Lido, Malamocco and Chioggia, and it can be divided into three basins. The first basin in the north part o f the lagoon has an area of 270 km 2 within which the city o f Venice is located. The second basin in the central part of the lagoon has an area of 160 km 2 and includes part of the industrial area of Port Marghera. The third basin is in the south part of the lagoon with a surface area o f 116 km 2 and includes the city o f Chioggia. 0048-9697/92/$05.00
© 1992 Elsevier Science Publishers B.V. All rights reserved
30
P. ZATTA ET AL.
The rivers and artificial canals that flow into the lagoon (Meneghin and Zamperoni, 1982) are the major contributors of the industrial, urban, and agricultural pollution found there. They carry the run-off from the reclamation and irrigation of the surrounding agricultural area. The construction of the industrial area of Port Marghera, the large-scale urban development of the Venice hinterland, and the massive utilization of chemicals in agriculture are the major reasons for the changing and worsening environmental conditions of the very fragile lagoonal ecosystem. Studies of the accumulation and distribution of trace elements in the Venetian lagoon have been done: Perin (1975) and Studio Tecneco (1978) analyzed the water, Giordani-Soika and Perin (1974) examined the sediments, while Barbaro et al. (1978), Moretti et al. (1979) and Campesan et al. (1980) used living organisms. The utilization of living organisms as the marine, and in more general way as the aquatic indicator of environmental pollution is now a well established technique (Goldberg, 1975) recognized by the International Monitoring Programs (IWM, 1980). In spite of the limitation of this approach due to the effects of variability of the physiological conditions of the aquatic medium on the living organisms (Morris, 1974; Phillips, 1976; Cossa et al., 1980), results achieved with this approach are of great interest in the evaluation of the water quality and consequently in detecting the degradation of the aquatic environment. Metal ions can occur in the aquatic environment under different forms (Fig. 1). The toxicity of a metal or of its compound in a biological system, depends upon different factors: (1) metal dose; (2) intrinsic toxicity; (3) binding capacity of the metal per se; (4) specificity of the biological system to
ORGANIC HYDROUTICALLY UNSTABLE COMPLEXES
ORGANIC STABLE ~. COMPLEXES
•
f
n+ Me
PARTICULATE
~OIDS
SEDIMENTS INORGANICCOMPLEXES
Fig. 1. Multiforms in which metal ions appear in aquatic environment.
EVALUATION OF HEAVY METAL POLLUTION IN THE VENETIAN LAGOON
31
transport of metal through a target organ; (5) biotransformation of a metal into a derivative and sometimes more toxic forms; and (6) ability of the living organism to sequester or secrete the metal, etc. Metal can otherwise modify the permeability of the cellular and subcellular membrane, the structure and function of proteins and nucleic acids, the metabolism of neuromodulators and hormones with a consequent influence on the homeostatic phenomena. The solubility of certain metals or of their compounds in water or in lipidic environment can influence their own accumulation in a biological system and consequently their toxic effect. The interaction of a toxic metal with a biological system is almost always complex. All these aspects must be kept in mind when living organisms are utilized as biological indicators of pollution. Biological monitors seem to be very useful tools due to the fact that the accumulation of heavy metals in aquatic organism is sometimes 103-106times higher with respect to the aquatic environment where the animals are sampled (Phillips, 1976). According to some authors (Haug et al., 1974) an ideal biological indicator of trace elements must have a sedentary or sessile existence, be abundant in the area of study and have relative longevity. Ease of sampling, tolerance to brackish water and the ability of accumulating pollutants with a high concentration factor are also important. There should be a strong correlation between metal accumulation and the metal concentration in the surrounding water. Mytilus species satisfies each of these conditions well. In this study, the mollusc Mytilus galloprovincialis has been utilized as a biomonitor of heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Hg, Pb, Zn) and non-metal (As) in the Venetian lagoon during some scientific cruises carried out in March, June and September 1988. As far as we know, this is the most complete study of the metal pollution in the Venetian lagoon carried out utilizing marine organisms as biological indicators. EXPERIMENTAL
Mytilus galloprovincialis was collected from 44 stations in March, June and September 1988, utilizing samples of 3-5 cm from natural population attached to the 'Briccole' that limit canals of lagoonal navigation. Sampling sites are indicated in Fig. 2 and correspond to the number in brackets in Table 1. All 'Briccole' carry a number which corresponds to our sampling sites, and is reported in Table 1 at the right of the location name. Once collected, samples were kept at 4°C during the time of transferring to the laboratory. All mussels were sampled according to the procedure described by Phillips (1976). About 10 individuals per station were collected each time. The shell was removed and the soft tissues digested in a mixture of HNO3/H2SO4
32
P. Z A T T A ET AL.
\ N
.jo:
./
\
/
!
.PORT. ENTRANCE LIDO
ADRIATIC
SEA
MALAMOCCO
NCE CHIOGGIA
i,:'i~:ii!:!
Fig. 2. Study area: numbers correspond to the sampling stations.
33
EVALUATION OF HEAVY METAL POLLUTION IN THE VENETIAN LAGOON
TABLE 1 The first numerical line reports the accumulation of metal ions and As in Mytilus galloprovincialis (#g/g of fresh wt) collected in different sampling stations [#] of the Venetian lagoon. The second numerical line represents the S.D. The number on the right of the sampling location represents the number marked on the 'Briccolas' which delimit the navigation canals As
Cd
Co
North basin [30] Cimitero 7 2,203 0.264 0.195 0.164 0.034 0.044
Cu
Cr
2.024 0,215
-
[31] Light of Murano Island 49 2.218 0.223 0.113 1.94 0.680 0.085 0.073 1.046
Fe
Hg
Mn
Ni
Pb
Zn
46.80 20.04
0.079 0.014
2.127 0.592
0.182 0.063
0.300 0.091
27.34 11.45
63.76 28.99
0.083 0.014
2.430 0.685
0.446 0.085
0.351 0.095
26.49 10.39
46.92 29.08
0.073 0.016
8.30 2.84
0.300 0.106
0.212 0.121
37.32 10.13
50.39 18.19
0.178 0.007
2,090 0,417
0.322 0.164
0.222 0.040
23.78 9.86
60.97 23.55
0.137 0.036
38,480 19.77
0.437 0.204
0.316 0.082
19.12 3.25
[32] S. Giacomo in Palude Island 3 2.272 0.625
0.300 0.203
0.197 0,088
1.60 0.72
-
[33]Madonna delMonte Island 26 2.353 0.186 0.178 1.872 0.20 0,124 0.108 0 . 0 8 1 0.521 0.08
[34]Mazzorbo Island 5 1.757 0.196 0.291 0.083
0.318 0.150
2.033 0.311 1.449 0.154
0,172 0.077
2.085 0,929
0.368 131.37 0 . 1 6 1 10.17
0.132 0.053
5.323 3.555
0.516 0.170
0.379 0.011
15.76 1.57
[36] Torcello Island 7 2.202 0.207 0.295 0.287 0.094 0.033
2.069 0.360
0,317 0.231
97.72 42.96
0.123 0.041
4.324 0.271
0.578 0.518 0 , 2 1 1 0.161
14.43 1.48
[37] Torcello Island 6 2.313 0.127 0.210 0.221 0.079 0.041
1,909 0.341
0.239 0.048
63,38 21.83
0,136 0,030
3 . 1 4 1 0,549 0.624 0.078
1.449 0.509 0.136 0.249
167,53 27,62
0,041 0,016
35.718 11.004
1.783 0.280 0.924 0.176
149.67 2.36
0,049 0.020
5.205 2.487
[35] Silone 35 1.615 0,196 0.520 0 . 0 8 1
0.212 0.121
14.97 2.07
0.530 0.128
0.246 0.041
24.96 2.12
0.300 0.106
0.299 0.100
16.23 6.77
[38] Canal of Burano Island 9 1.815 0.083 0.806 0.085
0,273 0.045
[39] Burano Island 10 1.877 0.151 0.806 0.072
0.248 0,002
34
P. ZA'I'fA ET AL
TABLE 1 As
(Continued)
Cd
Co
Cu
Cr
Fe
Hg
Mn
Ni
Pb
Zn
[40] Canal of Burano Island 15 1.552 0 . 0 5 1 0.438 0.048
0.082 0.032
1.082 0 . 4 1 1 107.64 0.624 0.374 51.26
0.130 0.020
5 . 0 1 1 0.334 1 . 4 7 1 0.127
0.351 0.095
15.83 7.97
1 . 4 9 9 0.213 0.060 0.075
98.98 11.44
0.133 0.009
4.700 2.492
0.513 0.079
0.519 0.207
23.75 7.62
[42] S. Francesco delDeserto Island 1.808 0.266 0.220 1.576 0.519 0.232 0.057 0.085 0.430 0.329
68.42 1.24
0.156 0.036
4.486 0.413 1 . 3 3 8 0.147
0.416 0.306
19.25 3.51
55.35 6.10
0.051 0.040
3.566 1.534
0.280 0.067
0.150 0.007
21.23 3.80
138.26 34.41
0.162 0.009
6.156 0.449 1 . 0 3 6 0.081
0.222 0.040
24.94 5.86
44.719 0.161 11.687 0.181
7.105 2.145
0.460 0.049
0.616 0.487
19.754 8.048
0.229 0.030
46.668 14.671
-
2.082 0.219
0.092 0.003
0.455 0.184
10.619 4.626
1.242 0.197 0.228 0.058
56.261 10.000
-
3.108 0.518
0.359 0.025
0.468 0.153
23.670 4.457
1.227 0.246 0.272 0.093
59.672 16.070
-
4.209 0.286
0.258 0.500 0 .0 1 1 0.016
27.687 6.972
1.759 0.274 0.948 0.146
68.543 9.601
0.043 0.003
3.992 0.757
0.392 0.177
0.526 0.126
18.881 1.882
1.846 0.183
59.508 9.878
-
2.381 0.772
0.268 0.084
0.445 0.123
20.368 4.885
[41]Gravan 72 2.592 1 . 6 3 6 0.101 0.490 0.014 0.103
[43] Sabbioni Point 43 2.284 0.650
0.165 0.081
0.151 0.035
1 . 2 3 0 0.107 0.294 0.005
[44] Certosa Island 4 2.216 0.560
0.169 0.044
0.310 0.095
1.586 0.254
0.585 0.050
[1] S. Servolo Island 5 1.477 0.146 0.365 2.530 0.448 0.0930 0 . 2 4 1 1.606
0.500 0.234
Cen~albasin
[2] S. Maria delleGrazie Island 12 0.940 0.319
0.190 0.115
0.321 0.282
0.723 0.117
[3] Sacca Sessola Island 8A 0.290 0.099
0.196 0.072
0.233 0.016
[4] S. Clemente Island 144 1.362 0.254 0.275 0.120
0.242 0.055
[5] S. Spirito Island 135 1.422 0.220 1.265 0.072
0.126 0.089
[6] Poveglia Island 78 0.902 0.070 0.130 0.142 0.018 0.004
0.154 0.024
35
EVALUATION OF HEAVY METAL POLLUTION IN THE VENETIAN LAGOON
TABLE 1 As
(Continued)
Cd
Co
Cu
Cr
Fe
Hg
[7]Malamocco 70 1.360 0.387 0.369 0.259 0.032 0.010
1.692 0.540
0.348 0.094
89.050 23.997
0.074 0.020
[8]Alberoni 31 1.315 0.197 0.263 0.350 0.094 0.025
1.061 0.091 0.361 0.009
59.638 16.320
Pb
Zn
5 . 5 2 1 0.687 2.069 0.062
0.661 0.221
12.656 1.561
0.064 0.017
4.411 0.603 1 . 3 0 8 0.412
0.850 0.257
18.236 5.574
0.017 0.005
3.186 0.096 1 . 2 5 2 0.029
0.261 0.014
16.295 2.602
-
2.303 0.953
0.602 0.118
17.095 2.638
2.852 0.773 1 . 0 1 2 0.215
0.691 0.214
14.934 1.997
0.556 0.087
16.088 2.284
[9]Alberoni Lighthouse 10 1.959 0.084 0.215 0.665 0.350 0.017 0.135 0.082
0.131 0.017
34.528 18.226
[10]Malamocco 16 1.525 0.066 0.192 0.122 0.004 0.012
0.926 0.236
0.204 0.021
108.374 56.944
[11] S. Leonardo Canal 232 1.089 0.242 0.120 0.012 0.193 0.188 0.051 0.339
0.296 0.023
103.187 0.045 1.936 0.018
Mn
Ni
0.388 0.134
[12] Lussario Canal 163 0.897 0.153 0.227 1.410 0 . 1 8 1 0.247 0.007 0.043 0.505 0.025
58.666 0.032 1 2 . 2 5 5 0.023
2.790 0.980
[13] Fusina 12 0.997 0.387 0.217 0.643 0.129 0.023
1.116 0.238 0.305 0.072
48.854 1.629
0.036 0.002
3 . 4 6 1 0.692 0.665 i.289 0.251 0.358
23.375 7.482
0.165 0.108
0.058 0.304
0.468 0.051
34.510 0.614
0.069 0.012
6.229 3.365
0.575 0.456
0.983 0.045
28.224 1.847
[15] Trezze Island 9 1.025 0.323 0.312 0.326 0.015 0.076
0.970 0.167
0.157 0.025
75.945 2.730
-
4.419 0.608
0.474 0.018
0.658 0.074
30.103 11.921
[16] S. Angelo delle Polverari Island 36 0.841 0.350 0.204 0.669 0.144 44.678 0.198 0.168 0.060 0.082 0.041 12.432
0.029 0.007
4.672 0.198 1 . 8 8 5 0.100
0.329 0.151
28.37 14.662
[17] Giudecca Island 3 0.816 0.135 0.255 1.755 0.196 0.115 0.026 0 . 0 1 1 0.650 0.054
0.033 0.001
6.247 1.30
0.33 0.110
[14] Port Marghera 68 1.110 0.734 0.460 0.072
43.241 5.330
0.240 0.435 0 . 1 0 1 0.081
17.022 4.192
36
P. ZATTA ET AL,
TABLE 1 As
(Continued)
Cd
Co
Cu
Cr
Fe
Hg
Mn
Ni
Pb
Zn
0.241 0.015
1.181 0.450
32.378 11.180
0.171 0.164
15.243 6.293
[18] S. GiorgioMaggiore Island 11 1.652 0.212
0.259 0.083
100.867 22.467
-
5.350 2.491
South lmsin [19] S. Pietro In V o l t a 2 3 1.271 0.047 0.288 0.029
0.529 0.195
1.939 1.100
-
1.256 0.213
0.121 0.043
0.763 0.087
18.057 3.263
-
2.498 0.050
0.101 0.039
0.219 0.092
18.542 4.581
-
0.169 0.119
0.991 0.195
2.323 0.410
-
3.490 1.894
-
0.364 0.094
17.060 5.490
-
0.173 0.080
0.822 0.168
23.997 15.582
-
2.333 0.082
0.123 0.050
0.422 0.092
15.153 3.012
[23] L o m b a r d o Canal 22 1.122 0.094 0.256 0.050
0.888 0.470
20.537 6.149
-
2.055 0.569
-
0.135 0.078
12.633 2.090
-
6.814 2.618
-
0.212 0.117
16.453 1.697
0.517 0.181
0.142 0.007
0.288 0.014
[20] S. Pietro di Pellestrina 70 1.159 0.063
0.052 0.007
-
[21]Pellestrina 138 1.337 0.504
0.058 0.004
[22] Caroman 21 1.063 0.124
0.028 0.016
[24] SS Romea 40 1.265 0.389
0.154 0.043
-
0.204 0.114
1.201 0.832
ND
[25] L o m b a r d o Canal 70 1.921 0.007 0.087 0.126 0.001 0.009
0.771 0.278
29.252 22.024
-
2.443 1.118
-
0.225 0.063
11.564 2.066
0.706 0.127
50.831 36.595
-
2.149 0.814
0.154 0.079
0.272 0.040
14.258 4.238
0.129 0.085
0.629 0.254
35.22 4.25
0.022 0.005
1.856 1.068
0.070 0.045
0.295 0.048
17.163 3.753
[28] Valgrande Canal 22 0.688 0.039 0.109 0.087 0.005 0.073
0.588 0.071
0.019 0.002
1.484 0.598
-
0.228 0.060
8.018 2.351
[26] Perognola Canal 248 0.960 0.184
0.019 0.009
0.044 0.002
0.195 0.103
[27] Perognola Canal 186 1.373 0.200
0.049 0.025
-
ND
37
EVALUATION OF HEAVY METAL POLLUTION IN THE VENETIAN LAGOON
TABLE 1 As
Cd
(Continued) Co
Cu
Cr
0.160 0.104
0.429 0.119
Fe
Hg
Mn
Ni
Pb
-
0.353 0.028
Zn
[29] Canale N u o v o 76 24.877 2.833
-
3.666 1.446
7.095 0.425
- , below detection limit. ND, not determined.
(Suprapur Merck) (5:1 v/v) at room temperature for 48 h, then heated at 70°C in reflux to complete the digestion. The digestion solution was diluted to a known volume and filtered through a 0.40/~m membrane. Metal determination was carried out by means of an atomic absorption spectrophotometer (Perkin-Elmer 4000), following the instrumental guidelines provided by the manufacturer. All analytical procedures were carried out according to the International Mussel Watch procedure (1980). Statistical analyses of the variance was done using the methods of Romeril (1971) and Phillips (1976). Other statistical analyses were carried out according to Johnel et al. (1967). RESULTS AND DISCUSSION
Bernardi et al. (1986) reported that every year about 414 tonnes of iron, 4 tonnes of nickel, 5.5 tonnes of copper, and 4.5 tonnes of lead are discharged into the Venetian lagoon. The total content of the heavy metals in the water consists of the soluble fraction and the fraction absorbed into the suspended particles (Fig. 1). Most of the metals introduced into the lagoon precipitate out as insoluble compounds since the water pH is alkaline, and consequently are deposited in the sediments. It has been observed that high metal concentrations of effluents coincide with the period of major water flow in the rivers which occurs between May and June and late autumn. Data reported here represent the average of the three sampling cruises. Results are expressed in /~g/g of fresh tissue. Table 1 shows the concentration of each metal in mussels collected from the different stations and grouped in each of the three basins A rsenic The most important industrial sources of As are the founderies and glass factories. In agriculture As is used in certain pesticides. We found a relatively high concentration of As in M. galloprovincialis in the north part of the
38
P. ZATTA ET AL.
lagoon (1.5-2.4 ppm) and lower concentrations in the central part of the lagoon (1.1-2.0 ppm) and in the south basin (1.0-1.5 ppm).
Cadmium Cadmium is released both from industrial and domestic waste. Industries with a potential output of cadmium are those involved in the production of non-ferrous metals. Bernardi et al. (1986) reported a high concentration of Cd in several effluents of the Venetian lagoon: 111 ppb in the Dese River, 206-330 ppb in the Osellino Canal, 130 ppb in the Trezze Canal with the highest concentration of 1096 ppb detected in the Naviglio-Brenta Canal. Values in our sampling are higher in the mussels collected in the central lagoon (0.2-0.7 ppm), lower in the north basin (0.05-0.3 ppm) and lowest in the south part (< 0.05 ppm). Our values are lower than the respective average values of 0.4 and 2.3 ppm reported a few years ago by Moretti et al. (1979) and Campesan et al. (1980).
Cobalt Seventy-five percent of the consumption of Co goes to the production of steel and alloys in the Veneto Region, and a marginal quantity is used in the fertilizers since low Co concentration in soil may induce Co deficiency among cattle. While the concentration of this metal is at the limit of instrumental detection in our samples from the southern part of the lagoon, in the north and central basins, values between 0.1 and 0.3 ppm were measured.
Copper The vast majority of copper is utilized by electrical industries of generators, telephones, electric power lines etc. The presence of Cu in our sampling ranges from 0.8 ppm in the south lagoon to 2.4 ppm as a higher concentration in the north lagoon (stations 30-37).
Chromium The presence of this metal in the environment is due exclusively to industrial production. It is worth noting that this chromium is utilized in the tanning industries located in the Vicenza area, a few kilometers from Venice, in numerous small and medium size industries in the Veneto Region and in the industrial area of Port Marghera. Values of chromium reported by other authors in M. galloprovincialis (Campesan et al., 1980) are in the order of 0.3-0.4 ppm, similar to our determinations in the central and south lagoon; higher values (0.6 ppm) were measured in the north basin.
EVALUATION OF HEAVY METAL POLLUTION IN THE VENETIAN LAGOON
39
Mercury Moretti et al. (1979) reported that fish from the Mediterranean sea contain high concentrations of Hg which is caused by a contribution of this metal to the sea from the mining area of Tuscany in the north-central part of Italy and Alpi Giulie in the north-western part of Italy close to the Yugoslavian border (Majori et al., 1973). Our values on Hg are between 0.05 and 0.18 ppm in the south lagoon and lower values were measured in the central basin (0.05 ppm) and, by limited instrumental detection, in the major number of our sampling stations. Values of Hg in the lagoonal effluents (Bernardi et al., 1986) show a higher concentration equal to 2120 ppb in the Osellino Canal, and 321.9 ppb in the Taglio Nuovissimo. These data, as specified by those authors, are due to occasional discharge or mixing of the sediments and do not represent a constant value of pollution.
Manganese Manganese compounds are used in steel alloys, in oxidizing-agent production, in the manufacture of dry batteries, electrical apparatus, ceramics, glass, fertilizers, and animal food additives. Almost all these activities are present in areas surrounding Venice and, consequently, they can be a potential hazard as sources of pollution. Manganese in our samples is between 2 and 6 ppm in the animals collected in the central lagoon, 1.5-4.0 ppm in those collected in the south lagoon and 5.0 ppm in those from the north basin. Average values reported by other authors correspond to our determinations (Campesan et al., 1980).
Nickel Our data on Ni accumulation in M. galloprovincialis give concentrations between 0.2 and 0.8 ppm in the north-central part of the lagoon and lower values in the south and central basin.
Iron In our analysis we found values of Fe accumulation in mussels ranging between 50 and 150 ppm in the north part of the lagoon, 50-100 ppm in the central basin and lower levels in the south lagoon.
Lead The development of industrialization and motorization is coincident with the increase of Pb pollution of the Venetian lagoon. The highest concentra-
40
P. ZATTA ET AL.
tion in the water was reported by Bernardi et al~ (1986) in the Osellino Canal in the range of 30-40 ppb. Concentration of Pb in the sediments was reported to be between four and eight times higher with respect to the average values, in the area of S. Angelo delle Polveri area, which corresponds to our sampling station No. 16 and in good agreement with our values of accumulation in M. galloprovincialis. Our determinations of Pb in the mussels used as biomonitor, range from 0.2 to 0.5 ppm in the north part of the lagoon, 0.4-1.1 ppm in the central basin and the lowest concentration was found in the south lagoon. Our data are lower than those reported by other authors (Campesan et al., 1980).
Zinc Zinc is utilized in the production of light alloys, rubber industries, paints and in some products for agriculture. Moretti et al. (1979) reported values of Zn in M. galloprovincialis at least double with respect to our findings. CONCLUSIONS
The industrial and economic structure of the Veneto Region is characterized by an enormous development and concentration of small and medium size industries which have created some difficulty in controlling the environmental pollution. The Venetian lagoon is a fragile ecosystem with particular characteristics heavily impacted by the Port Marghera, one of the largest industrial areas in Europe, and by the city of Venice. The lagoon is the final part of a drainage basin which carries waste from farming and agricultural activities. In view of the importance of the Venetian lagoon, both from the economic and from the historical standpoints, we carried out this study of biomonitoring and analyzing the accumulation of As and the heavy metal ions in
Mytilus galloprovincialis. Data of highest accumulation were found in the north part of the lagoon and the lowest values concern the south basin. This seems reasonable with the geographical position of rivers and canals and the consequent introduction of pollutants. ACKNOWLEDGEMENTS
Authors acknowledge Mr. Benito Bonora of the Istituto di Biologia del Mare, Venice, of the National Research Council of Italy, for the technical support during the sampling and the ECOLAB laboratory, Padova, Italy for the analysis of arsenic and lead.
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