biomonitoring of metal availability in the southern basin of the lagoon of venice (italy) by means...

BIOMONITORING OF METAL AVAILABILITY IN THE SOUTHERNBASIN OF THE LAGOON OF VENICE (ITALY) BY MEANS OF

MACROALGAE

NOEMI FAVERO∗ and MARIA GRAZIA FRIGODepartment of Biology, University of Padova, Padova, Italy

(∗ author for correspondence, e-mail: [email protected], fax: 39 049 8276300)

(Received 27 March 2001; accepted 23 January 2002)

Abstract. Macroalgae of the following species: Ulva laetevirens, Enteromorpha intestinalis, Gra-cilaria verrucosa and Sargassum mutycum, were used to monitor metal concentrations (Al, Mn, Fe,Cu, Zn, Cr, Co, Ni, Cd) in the waters of the southern basin of the Lagoon of Venice. Sampling wasperformed at 5 sites, gradually moving north from the town of Chioggia. Species-specific seasonalvariability was observed, with significant increases of Cd in U. laetevirens in January, Al and Pbin E. intestinalis in May, and Al and Ni in S. mutycum in January. Seasonal relative frequencies ofmetal peak concentrations emphasize the occurrence of Pb peaks in May for all the studied species.Analysis of inter-site variability shows significant increases of Al, Fe, Cr and Pb in U. laetevirens atthe Hydro-Biological Station, located within the town of Chioggia. Metal concentrations in algae arecomparable with those in other areas of the lagoon, although Fe, Cr and Ni concentrations are lowerthan in the northern and central basins. This result fits dissolved metal concentrations determined byother authors, but does not correspond to the reported presence of Cr in the sediments of the southernbasin. The hypothesis is discussed according to which low Cr levels in algae reflect Cr speciation insediments.

Keywords: algae, metals, pollution, Venice

1. Introduction

The Lagoon of Venice, an interface between land and sea, clearly represents coastalenvironments heavily affected by anthropogenic pollution in other parts of theworld (Chua, 1997). It is a semi-enclosed body of water with a surface area ofabout 500 km2, connected to the Adriatic Sea through the three ‘mouths’ of Lido,Malamocco and Chioggia. The lagoon exchanges water and sediments with the seaaccording to tidal cycles.

From a geological point of view, the lagoon is characterized by a network ofchannels of various depths, estuaries, tidal marshes and mud flats; the mean waterdepth is about 0.6 m, and the tidal range is less than 1 m. The average waterturnover is two days, and water dynamics decrease near the mainland (Frignaniet al., 1997).

This shallow-water system receives contaminants from rivers, streams, landrunoff, wastewater inputs, industrial discharges and from the atmosphere.

Water, Air, and Soil Pollution 140: 231–246, 2002.© 2002 Kluwer Academic Publishers. Printed in the Netherlands.

232 N. FAVERO AND M. G. FRIGO

Heavy metals are present among the toxic elements produced by industrial andanthropogenic pollution. The horizontal distribution of heavy metals in the sedi-ments of the Lagoon of Venice is reported by Donazzolo et al. (1984) and indicatestheir common origin in the industrial area of Marghera, from where the metalsare mobilised to larger lagoon areas by biological and physical processes (Luoma,1995). Only the extreme southern part of the lagoon, south west of the town ofChioggia, still seems to be unaffected by industrial pollution. But chromium, whichis described in moderate concentrations only in the sediments of the southern basin,probably reaches the lagoon from the Adriatic Sea through the Chioggia port en-trance. Basu and Molinaroli (1994) used these data to mathematically verify thehypothesis that tidal circulation in the Lagoon of Venice is the primary controlagent of toxic metal distribution.

However, knowledge of sediment metal distribution does not permit us to de-termine the real extent of bioavailable metals and, consequently, to state the riskof their introduction into the alimentary chain, since sediment composition is verycomplex and varies according to rates of deposition, particle size, rate of particlesedimentation, and presence of organic matter (Blackmore, 1998). Determinationof dissolved bioavailable metals is not easy and requires speciation studies in orderto discriminate free metal ions from those which are either inorganically or organ-ically complexed (Martin et al., 1995), as different organisms and species showdifferent response mechanisms to metal ions in solution (Bryan and Langston,1992).

Metal biomonitors are organisms which accumulate metals in their tissues andmay therefore be analysed as a measure of bioavailability of metals in the ambienthabitat (Rainbow, 1995). The ability to concentrate metals observed in many mac-rophytic algae has indicated their use as biomonitors in coastal areas all over theworld. Seaweeds respond essentially to dissolved metals only (Rainbow and Phil-lips, 1993): the choice of the ideal species is based on the condition that the organ-isms are not able to regulate metal uptake, and so passively reflect environmentalmetal availability and provide a time-integrated measure of metal supply over longperiods of time (weeks, months or even years) depending on the species (Phillipsand Segar, 1986). Based on the hypothesis that suitable biomonitors should exhibitthe same correlations between contaminant content and ambient concentrations atall locations and in all conditions, comparisons should be performed between thedifferent sites at the same time, or at the same sites on successive occasions in anyenvironmental monitoring project.

Ulva spp. and Enteromorpha spp., both belonging to the Ulvaceae family, havebeen extensively used to monitor environmental contamination in various geo-graphical areas (Drude de Lacerda et al., 1985; Sawidis and Voulgaropoulos, 1986;Ho, 1990; Schuhmacher et al., 1995; Leal et al., 1997; Blackmore, 1998; Muse etal., 1999). Ulvaceae have also been used in environmental contamination studiesof central (Sfriso et al., 1995) and northern areas (Palude della Rosa, marsh) of theLagoon of Venice (Favero et al., 1996).

METALS IN MACROALGAE FROM THE LAGOON OF VENICE (ITALY) 233

In this study, many species of macroalgae have been collected in order to mon-itor the availability of dissolved metals in the southern basin which, on the basisof sediment analysis, shows contamination levels partially comparable to northernand central basins (Donazzolo et al., 1984).

2. Materials and Methods

The study area is situated in the southern basin of the Lagoon of Venice, near thetown of Chioggia. Algae were collected from 5 sites gradually moving away fromChioggia (Figure 1): Lombardo Channel (site 1) and Hydro-Biological Station(site 2) within the town, San Felice Fort (site 3) and Ca Roman (site 4), respectivelyplaced south and north of the port entrance and Ca Roman Octagon (site 5) to thenorth in the lagoon. Samples of Enteromorpha intestinalis were collected once ina short branch of the Lombardo Channel, called Lombardo Vena (site 1a).

According to both the growth cycles of the studied species and the technicalpossibility of collecting samples, in particular the atmospheric conditions, the fourseasons of the year were monitored as follows: June 1994 (summer), Septem-ber 1994 (autumn), January 1995 (winter) and May 1995 (spring). Sampling wascarried out at low tide.

Four species of macroalgae were collected, which have been consistently foundin the lagoon over the last few years, though with varying distribution (Sfriso etal., 1993; Sfriso et al., 1994). Most of them may be considered as cosmopol-itan species, well adapted to the lagoon environment, characterized as it is bywidespread pollution and heavily euthrophized (Bendoricchio et al., 1993). Thespecies are: Ulva laetevirens (Areschouf) and Enteromorpha intestinalis (L.) Link(Chlorophyta), Gracilaria verrucosa (Hudson Papenfuss) (Rhodophyta) and Sar-gassum mutycum (Yendo) (Phaeophyta). The latter is a native species of Japan, firstcollected in the Mediterranean in 1980 and now widespread within the Lagoon ofVenice, but mainly in the southern basin near Chioggia (Curiel et al., 1995). In thediscussion, data relating to preliminary irregular samplings of E. intestinalis, U.laetevirens and G. verrucosa, performed during 1992 and 1993 at the same sites,will also be reported.

Whole plants were collected by hand from rocky substrates and by means of ascraper from sandy sediments. Approximately 250 g of each species were collectedeach time.

In S. mutycum, the apices of the ultimate branchlets were separated from therest of the plant in order to study differences in metal contents in relation to plantage.

Samples were directly washed in seawater at the sampling sites and transferredto the laboratory in polyethylene boxes under refrigeration (4 ◦C). After their ar-rival at the laboratory, they were washed carefully in seawater to remove sand,particulate matter, and epiphytal and epifaunal species. Then they were rapidly


Figure 1. Map of the sampling sites at Chioggia (Lagoon of Venice).


rinsed in bidistilled water (Milli Q), lyophilized and pulverized, and finally frozenat –20 ◦C until the moment of metal analysis.

Three subsamples (0.150 g) of each sample were submitted to acid digestionusing 70% HNO3 ARISTAR (BDH) in a Teflon-lined vessel by means of a mi-crowave oven (CEM model MDS-2000) in pressure-controlled conditions. Diges-ted samples were diluted to 50 mL with bidistilled water (Milli Q) and analysedfor metal contents. Analysis of aluminum (Al), copper (Cu), chromium (Cr), cobalt(Co), nickel (Ni), cadmium (Cd) and lead (Pb) were performed with a Zeemanflameless atomic absorption spectrophotometer (Perkin-Elmer model 5100 PC,equipped with an HGA 600 Graphite Furnace and a A560 autosampler). Man-ganese (Mn), iron (Fe), Cu and zinc (Zn) were analysed by flame atomic absorptionspectrophotometer (Perkin-Elmer model 4000). Al and Pb analysis was performedseparately to avoid sample contamination. Procedural blanks were run within eachbatch. Algal samples of certified metal composition (Lagarosiphon major AP1,CEE Common Research Center, Ispra, Italy) were employed as standard referencematerials to verify the analytical quality of metal determinations. Analytical preci-sion gave a mean error of 5%. Variability between months and sampling sites wasstatistically analysed for each metal by a one-way ANOVA.

3. Results and Discussion

3.1. SEASONAL VARIABILITY

Table I shows the complete set of data measured with regard to the Lagoon ofChioggia. U. laetevirens was the species most frequently sampled (18 collections),followed by G. verrucosa (11), E. intestinalis (9) and S. mutycum (8). This pat-tern of frequencies agrees with the dominant growth, in the Lagoon of Venice, ofUlvaceae (Sfriso et al., 1992, Sfriso et al., 1993). G. verrucosa was extensivelycollected, although it highly dominates near the edges of the channel outlets wherethe water currents affect algal growth and where particulate suspension and set-tlement are high. Gracilaria indeed is adapted to these environmental conditionsbecause of its ribbon like structure (Sfriso et al., 1994). As regards the other spe-cies, characteristic growth cycles were observed: E. intestinalis proliferates both inlate spring and in autumn, S. mutycum grows from winter to late spring.

In U. laetevirens seasonal mean metal concentrations (Figure 2) do not showsignificant variations for most of the metals, with the exception of Cd, whose levelis higher in winter time. Therefore, these metal trends do not allow us to confirm theseasonal differences in metal accumulation described for U. rigida sampled in thePalude della Rosa during the years 1992 and 1993 (Favero et al., 1996). However,environmental differences together with different collection strategies may wellexplain such variance, as well as possible inter-specific differences.


TAB

LE

I

Met

alco

ncen

trat

ions

(µg

g−1

dry

wt.)

inm

arcr

oalg

aefr

omC

hiog

gia

Sit

eM

onth

Al

Mn

Fe

Cu

Zn

Cr

Co

Ni

Cd

Pb

U.l

aete

vire

ns

1Ju

ne19

9475

1±10

545

.00±

4.02

510±

6.66

10.9

1±0.

8433

.0±0

.06

1.95

±0.0

20.

27±0

.02

1.80

±0.8

40.

07±0

.05

3.22

±0.2

0

Sep

t.19

94n.

d15

.00±

0.39

109±

1310

.88±

0.95

24.0

±0.7

20.

50±0

.05

0.25

±0.0

32.

02±0

.19

0.10

±0.0

21.

48±0

.23

Jan.

1995

827±

5737

.00±

0.07

594±

326.

97±0

.34

33.0

±1.2

31.

59±0

.09

0.50

±0.0

42.

26±0

.12

0.17

±0.0

03.

93±0

.16

May

1995

390±

328.

23±0

.21

239±

208.

06±0

.48

94.0

±4.2

50.

56±0

.03

0.18

±0.0

21.

51±0

.06

0.09

±0.0

02.

30±0

.05

2Ju

ne19

9416

48±2

2542

.00±

8.03

1020

±183

9.07

±1.3

127

.0±3

776.

94±0

.15

0.57

±0.0

93.

68±0

.36

0.03

±0.0

05.

49±1

.01

Jan

1995

2133

±224

33.0

0±1.

4284

1±23

7.29

±0.9

945

.0±1

.03

5.78

±0.4

80.

52±0

.04

2.87

±0.1

80.

17±0

.02

9.58

±0.1

0

May

1995

1972

±42

20.0

0±0.

7097

8±23

14.7

1±0.

1969

.0±1

.67

1.87

±0.1

40.

20±0

.01

1.21

±0.0

40.

09±0

.00

27.5

0±0.

53

3Ju

ne19

9415

2±10

115.

00±1

219

5±10

12.6

6±0.

0624

.0±0

.18

0.76

±0.3

91.

26±0

.17

3.99

±0.5

40.

03±0

.01

2.55

±0.7

5

Sep

t.19

9448

8±28

17.0

0±1.

2446

4±19

5.63

±0.3

525

.0±1

.89

1.74

±0.1

00.

12±0

.02

1.85

±0.0

30.

04±0

.01

2.32

±0.1

7

Jan.

1995

112±

868

186.

00±8

.73

285±

2219

.19±

0.64

43.0

±2.5

50.

54±0

.07

1.93

±0.0

83.

76±0

.41

0.17

±0.0

24.

17±0

.08

May

1995

126±

3.65

28.0

0±0.

8925

8±1.

9912

.56±

0.33

23.0

±0.3

90.

39±0

.04

0.57

±0.0

02.

19±0

.10

0.05

±0.0

03.

49±0

.42

4S

ept.

1994

121±

1514

8.00

±2.6

929

0±6.

506.

63±0

.48

8.5±

0.40

0.92

±0.5

51.

65±0

.08

6.10

±0.3

20.

11±0

.00

2.41

±0.0

5

Jan.

1995

93±6

.08

39.0

0±23

127±

3.35

13.8

4±1.

8230

.0±3

.85

0.31

±0.0

50.

63±0

.11

1.67

±0.2

60.

47±0

.11

2.39

±0.4

5

May

1995

269±

4027

.00±

2.31

326±

9.37

7.30

±0.3

417

.0±0

.57

0.68

±0.0

30.

54±0

.05

2.27

±0.0

50.

06±0

.00

3.29

±0.3

4

5Ju

ne19

9485

±8.5

934

.00±

4.01

203±

404.

91±0

.40

13.0

±0.5

20.

92±0

.26

0.57

±0.0

02.

96±0

.05

0.04

±0.0

01.

83±0

.12

Sep

t.19

9410

3±10

225.

00±8

.61

346±

7412

.49±

1.52

29.0

±1.7

91.

16±0

.19

1.30

±0.2

75.

36±0

.88

0.22

±0.0

04.

94±0

.18

Jan.

1995

334±

3344

.00±

0.34

491±

419.

80±2

.09

43.0

±8.1

41.

28±0

.15

0.73

±0.0

12.

54±0

.12

0.22

±0.0

26.

03±1

.44

May

1995

539±

477.

09±0

.71

288±

257.

09±0

.66

16.0

±1.2

51.

06±0

.07

0.29

±0.0

21.

45±0

.08

0.06

±0.0

01.

90±0

.19

Val

ues

expr

esse

das

mea

ns±S

Dof

thre

ean

alys

es.


TAB

LE

I

(con

tinu

ed)

Sit

eM

onth

Al

Mn

Fe

Cu

Zn

Cr

Co

Ni

Cd

Pb

E.i

ntes

tina

lis

1S

ept.

1994

9.79

±3.4

921

±2.3

411

7±5.

1111

.4±0

.86

14±1

.18

0.54

±0.2

80.

26±0

.04

3.72

±0.5

40.

07±0

.02

1.06

±0.1

7

May

1995

11.0

0±2.

3220

±1.8

571

6±86

11.2

±0.7

261

±2.0

02.

69±0

.19

0.33

±0.0

41.

99±0

.21

0.13

±0.0

05.

78±0

.57

1aS

ept.

1994

n.d.

20±0

.37

61±0

.85

14.3

±0.3

320

±1.3

50.

47±0

.09

0.29

±0.0

32.

07±0

.17

0.04

±0.0

10.

54±0

.05

May

1995

1673

.00±

136

27±2

.07

1011

±63

15.4

0±1.

0939

±1.0

93.

49±0

.02

0.40

±0.0

92.

05±0

.20

0.06

±0.0

03.

74±0

.13

2S

ept.

1994

21.0

0±0.

2726

±3.6

815

4±14

20.6

±1.3

538

±8.0

81.

42±0

.53

0.14

±0.0

12.

04±0

.32

0.13

±0.0

20.

46±0

.23

May

1995

2732

.00±

235

29±0

.06

1778

±142

39.1

±2.3

677

±5.0

66.

06±0

.67

0.24

±0.0

11.

92±0

.09

0.09

±0.0

115

.96±

0.59

3S

ept.

1994

39.0

0±9.

8345

±2.2

626

6±18

12.7

±3.0

136

9±2.

570.

45±0

.09

0.74

±0.0

50.

54±0

.00

0.84

±0.0

11.

28±0

.07

May

1995

1212

.00±

3232

±1.2

579

6±44

12.3

±0.0

048

±1.3

62.

74±0

.34

0.23

±0.0

41.

76±0

.06

0.06

±0.0

18.

13±0

.60

5S

ept.

1994

173.

00±9

.69

27±3

.69

183±

8.11

3.69

±0.6

526

±1.7

30.

31±0

.02

0.40

±0.0

32.

35±0

.13

0.07

±0.0

11.

23±0

.25

May

1995

6.00

±0.8

914

±0.9

241

6±45

4.87

±0.5

122

±1.6

81.

15±0

.00

1.18

±0.0

01.

54±0

.09

0.08

±0.0

02.

78±0

.11

G.v

erru

cosa

1S

ept.

1994

n.d

270±

8.78

327±

8.35

1.44

±0.1

910

±0.8

70.

55±0

.11

2.67

±0.0

91.

13±0

.11

0.05

±0.0

24.

13±0

.12

3Ju

ne19

9423

.00±

0.69

77±2

.55

116±

8.02

2.38

±0.6

933

±0.9

70.

44±0

.13

0.31

±0.1

3n.

d.0.

08±0

.02

2.26

±0.4

5

Sep

t.19

9414

9.00

±0.0

051

±2.3

117

0±2.

913.

15±0

.33

28±1

.67

9.52

±2.0

80.

26±0

.10

3.55

±0.9

00.

15±0

.02

1.12

±0.1

5

Jan.

1995

40.0

0±19

66±2

.65

360±

114.

88±0

.41

46±3

.32

0.48

±0.0

40.

40±0

.03

0.28

±0.0

30.

16±0

.02

3.64

±1.1

2

May

1995

52.0

0±6.

4619

7±2.

3921

0±1.

015.

31±0

.34

45±0

.41

0.52

±0.0

21.

03±0

.07

0.33

±0.0

10.

11±0

.00

5.80

±0.6

0

4S

ept.

1994

128.

00±7

.84

77±1

.98

405±

123.

80±0

.01

21±0

.20

5.68

±0.7

30.

63±0

.05

3.92

±0.2

10.

17±0

.05

2.56

±0.1

0

Jan.

1995

24.0

0±4.

8812

±0.6

9n.

d4.

32±0

.27

22±2

.08

n.d.

0.05

±0.0

10.

45±0

.05

0.08

±0.0

10.

76±0

.10

May

1995

88.0

0±2.

8319

±0.6

413

0±2.

211.

88±0

.19

20±0

.25

0.17

±0.0

00.

03±0

.00

0.33

±0.0

20.

04±0

.00

1.41

±0.0

6

Val

ues

expr

esse

das

mea

ns±S

Dof

thre

ean

alys

es.


TAB

LE

I

(con

tinu

ed)

Sit

eM

onth

aA

lM

nF

eC

uZ

nC

rC

oN

iC

dP

b

5S

ept.

1994

19.0

0±5.

5177

±0.6

813

0±1.

3410

.89±

1.10

28±0

.55

0.30

±0.0

50.

24±0

.03

0.50

±0.0

40.

12±0

.03

0.81

±0.1

2

Jan.

1995

58.0

0±4.

2125

±1.5

729

5±8.

076.

44±0

.41

19±0

.93

0.35

±0.4

00.

08±0

.01

0.83

±0.1

0.10

±0.0

13.

50±0

.15

May

1995

52.0

0±1.

8527

±0.8

719

3±15

3.32

±0.3

332

±1.0

10.

31±0

.03

0.11

±0.0

00.

33±0

.03

0.12

±0.0

02.

00±0

.21

S.m

utyc

um

1Ja

n.19

95Y

321±

828.

44±1

.01

420±

5616

.90±

1.95

71±5

.91

0.32

±0.1

40.

22±0

.11

1.21

±0.3

81.

55±0

.19

2.98

±0.1

4

Jan.

1995

O55

0±64

23.0

0±2.

0144

7±23

7.93

±0.2

746

±4.9

10.

95±0

.15

0.47

±0.0

31.

99±0

.23

0.63

±0.0

43.

62±0

.18

May

1995

Y30

±0.3

77.

27±0

.68

68±0

.98

3.47

±0.2

533

±1.3

20.

07±0

.00

0.49

±0.0

31.

04±0

.03

1.25

±0.1

01.

42±0

.10

May

1995

O71

±7.6

617

.00±

0.66

180±

2016

.96±

0.88

46±0

.99

0.39

±0.0

10.

91±0

.02

1.51

±0.1

40.

81±0

.06

2.32

±0.0

5

2Ju

ne19

9412

1±41

188.

00±7

.86

117±

2.34

44.4

5±4.

3231

1±11

.60.

96±0

.15

0.49

±0.2

60.

86±0

.20

0.26

±0.0

11.

10±0

.00

Jan.

1995

Y12

8±2.

9726

.00±

0.23

270±

137.

17±0

.82

43±0

.45

0.55

±0.0

40.

34±0

.00

1.23

±0.0

91.

06±0

.09

1.42

±0.0

8

Jan.

1995

O28

1±63

84.0

0±6.

6571

0±18

38.

93±2

.01

43±0

.31

1.31

±0.3

50.

93±0

.17

2.28

±0.3

30.

39±0

.00

2.76

±0.5

7

May

1995

Y44

±4.0

316

.00±

0.32

111±

3.43

5.41

±0.5

211

2±1.

220.

18±0

.00

0.22

±0.0

10.

39±0

.00

0.67

±0.0

316

.45±

0.36

May

1995

O86

±5.8

516

.00±

0.01

182±

184.

64±0

.02

87±7

.63

0.21

±0.0

10.

35±0

.02

0.63

±0.0

60.

57±0

.00

16.4

4±0.

15

3Ju

ne19

9417

5±12

30.0

0±0.

5987

±15

1.27

±0.3

833

±0.2

70.

49±0

.17

1.18

±0.0

50.

84±0

.08

0.46

±0.1

30.

86±0

.07

Jan.

1995

Y24

2±21

24.0

0±0.

0216

5±11

7.63

±0.6

664

±0.5

40.

48±0

.03

0.26

±0.0

20.

79±0

.08

1.33

±0.0

70.

98±0

.07

Jan.

1995

O47

2±42

72.0

0±4.

8218

2±1.

384.

95±0

.91

23±1

.11

0.50

±0.0

20.

80±0

.07

1.59

±0.1

70.

34±0

.00

1.20

±0.0

2

May

1995

Y85

±11

14.0

0±0.

3612

5±0.

837.

79±0

.21

56±1

.47

0.08

±0.0

40.

40±0

.03

0.63

±0.0

61.

13±0

.130

2.01

±0.2

7

May

1995

O10

3±72

27.0

0±0.

0017

9±0.

728.

15±0

.24

74±0

.13

1.18

±0.0

20.

34±0

.00

0.73

±0.0

50.

67±0

.03

3.00

±0.4

2

Val

ues

expr

esse

das

mea

ns±S

Dof

thre

ean

alys

es.

aY

=yo

ung,

O=

old.


Fig

ure

2.M

ean

seas

onal

conc

entr

atio

nsof

the

met

als

inm

acro

alga

efr

omC

hiog

gia:

Y=

youn

g,O

=ol

d,st

atis

tica

lsig

nifi

canc

e(∗)

p<

0.05

.


In E. intestinalis, the seasonal mean significantly differs (p < 0.05) for Al, Znand Pb and higher mean metal concentrations of Al, Fe, Cr and Pb occur in spring(May) (Figure 2).

As regards S. mutycum, most of the metals show higher concentrations in theoldest parts of the plants (the basal portion of branches and the stipe) and lowerconcentrations in the youngest ones (the apices), with the exception of Cu, Znand Cd. The apices show higher metal levels in January (Al, Mn, Fe, Cu, Cr, Ni,Cd) with significant differences (p < 0.05) in Al and Ni. Significant differences inresults for Al and Ni were also in the oldest parts of the plants (Figure 2). Thesemetal trends may be due both to the biological cycle of S. mutycum, which beginsits growth in winter, and to specific bioavailability conditions. Riget et al. (1995)suggest that primary production may control Cd concentrations in the surface wa-ters, thus inducing an increase in Cd bioavailability in the cold season, when themetal is released back into water. The slow growth of plants in winter also impliesthe longer permanence of thalli in the water and prolongs exposure to dissolvedmetals (Shimshock et al., 1992). In the present study, in which algae from varyingtaxa were examined, winter metal increases seem to depend mainly on the differentbiological cycles and the metal bioavailability conditions.

Despite interspecies differences, Figure 2 shows higher mean Pb levels in Mayfor all the studied species. Therefore, in order to draw final conclusions about theseasonal metal trends, seasonal relative frequencies of peak concentration valueswere calculated for each metal, as algae species were not collected uniformlyrelative to seasons and sites.

Calculation of the relative frequencies was performed for each season and eachmetal. It is based on the ratio between the number (n) of peaks of each metal in eachseason, taking into consideration all the studied species (in this study n will not begreater than 4), and the total number (N) of peaks among all studied metals in thatseason, taking into consideration all the studied species. N is a number which isderived from the number of studied species and the number of determined metalsand, in this study, is: 6 in June, 15 in September, 10 in January and 9 in May. Thecalculated ratios emphasize that peak Pb values were measured in May (n = 4) forall the considered species (Figure 3). A possible increase of atmospheric Pb fall-out, as a direct consequence of the rainy season, may be the origin of this. Cochranet al. (1998) indeed point out that atmospheric input dominates Pb input to thelagoon, except near the mainland industrial area.

With the other metals, peak relative frequencies are distributed differently amongthe four seasons: toxic metals Al and Cd show higher frequencies in winter, whereasthe essential metals (Mn, Fe, Cu, Zn, Cr, Co and Ni) in warm weather (June andSeptember) when light exposure and temperature activate metabolic rates.


Figure 3. Seasonal relative frequencies of the metal peaks in macroalgae from Chioggia.

3.2. SAMPLING SITE VARIABILITY

U. laetevirens showed significantly higher levels of Al (p < 0.001), Fe (p < 0.001),Cr (p < 0.01) and Pb (p < 0.05) at site 2 (Hydro-Biological Station) (Figure 4).E. intestinalis also presented higher values (Fe, Cu, Cr, Pb) at this site, but thedifference was significant only for copper. Similarly, S. mutycum showed higher Pbconcentrations at site 2. As regards G. verrucosa, which was not present at site 2,some of its higher values (including Pb), were at site 1 (Lombardo Channel), insidethe town.

In conclusion, some typical trends in metal distribution appear quite evident: a)lower concentrations at site 5 (Ca Roman Octagon), far from the town, with a fasterwater turnover; and b) recurrence of higher metal concentrations at site 2, probablydue to a slower water turnover in front of the Hydro-Biological Station.

3.3. COMPARISON WITH OTHER AREAS OF THE LAGOON OF VENICE AND

THE ADRIATIC SEA

For the three species described in Table II, the mean concentration values of Fe, Crand Ni were lower than those reported for algae collected either from the centralbasin of the Lagoon of Venice (Sfriso et al., 1995) or from the northern one (Faveroet al., 1996).

These data fit those published by Scarponi et al. (1998) who report unexpectedlow levels of Cr, Fe and Ni dissolved in the water of the southern basin. Theseauthors however describe the sediments of the southern lagoon as richer in Ni,Fe and Cr. The reason for this apparent discrepancy may be partially explained ifspeciation analysis of sediments is taken into deep account. In fact, in the study of


Fig

ure

4.M

ean

site

conc

entr

atio

nsof

the

met

als

inm

acro

alga

efr

omC

hiog

gia:

Y=

youn

g,O

=ol

d,st

atis

tica

lsig

nifi

canc

e(∗)

p<

0.05

,(∗∗

)p

<0.

01,(

∗∗∗)

p<

0.00

1.


TAB

LE

II

Mea

nm

etal

conc

entr

atio

ns(µ

gg−

1dr

yw

t.)in

mac

roal

gae

from

the

Lag

oon

ofV

enic

e(V

L)

and

the

Adr

iati

cS

ea(A

S)

Ref

eren

ceF

eC

rN

iC

uC

dP

b

Ulv

asp

p.

Palu

dede

lla

Ros

a(V

Lno

rth)

(Fav

ero

etal

.,19

96)

912

2.67

4.39

8.89

0.14

2.43

Chi

oggi

a19

92–1

993

(VL

sout

h)(F

aver

o,un

publ

ishe

dda

ta)

481

1.57

3.29

120.

1

Chi

oggi

a19

94–1

995

(VL

sout

h)(T

his

stud

y)42

01.

612.

749.

990.

124.

93

Alb

eron

i(V

Lce

ntra

lbas

in)

(Sfr

iso

etal

.,19

95)

1904

7.9

9.5

0.22

2.6

Sac

caS

esso

la(V

Lce

ntra

lbas

in)

(Sfr

iso

etal

.,19

95)

1750

8.2

14.5

0.09

1.4

San

Giu

lian

o(V

Lce

ntra

lbas

in)

(Sfr

iso

etal

.,19

95)

4240

10.0

522

.04

0.16

4.09

Rav

enna

(AS

)(L

ocat

elli

etal

.,19

99)

230.

096.

96

Po

rive

rde

lta

(AS

)(L

ocat

elli

etal

.,19

99)

270.

155.

69

Istr

ia(A

S)

(Mun

da,1

991)

8.00

0.30

E.i

ntes

tina

lis

Chi

oggi

a19

92–1

993

(VL

sout

h)(F

aver

o,un

publ

ishe

dda

ta)

411

1.37

4.73

150.

04

Chi

oggi

a19

92–1

995

(VL

sout

h)(T

his

stud

y)55

01.

931.

9914

.55

0.15

4.09

Alb

eron

i(V

Lce

ntra

lbas

in)

(Sfr

iso

etal

.,19

95)

2444

13.7

8.9

2.80

<0.

051.

70

San

Giu

lian

o(V

Lce

ntra

lbas

in)

(Sfr

iso

etal

.,19

95)

4190

15.1

720

.40.

063.

6

G.v

erru

cosa

Palu

dede

lla

Ros

a(V

Lno

rth)

(Fav

ero,

etal

.,19

96)

353

3.62

5.66

9.77

0.29

Chi

oggi

a19

92–1

993

(VL

sout

h)(F

aver

o,un

publ

ishe

dda

ta)

379

0.67

1.18

4.47

0.10

Chi

oggi

a19

94–1

995

(VL

sout

h)(T

his

stud

y)23

41.

911.

924.

350.

112.

54

Alb

eron

i(V

Lce

ntra

lbas

in)

(Sfr

iso

etal

.,19

95)

530

7.9

9.1

5.4

0.25

1.1

San

Giu

lian

o(V

Lce

ntra

lbas

in)

(Sfr

iso

etal

.,19

95)

1790

4.4

3.6

16.3

0.24

6.6


Scarponi et al. (1998), total metal amounts are reported together with those boundto three fractions: (A) ionic exchangeable form and carbonate fraction, (B) metalsbound to Fe-Mn oxides, (C) metals bound to sulphides and to the organic phase.These fractions are distributed in nature from the top of the sediments, the oxiczone, down to anoxic (reduced) sediments (Luoma, 1995). Chromium and nickelincrease their concentration from (A) to (C), indicating that these metals are moreabundant in anoxic sediments and, consequently, are less available for suspensionin water. As regards toxic metals Cu, Pb and Cd, typical expressions of industrialand urban pollution, E. intestinalis and Ulva show mean concentration values sim-ilar to those in the central and northern basins. These data fit the levels of dissolvedCd and Cu reported by Scarponi et al. (1998), which are similarly distributed fromthe mainland towards the sea, with a peak only in the industrial area of Marghera.

The relative homogeneity in Pb levels within the Lagoon of Venice, as well asin the northern Adriatic Sea, (Munda and Hudnick, 1991, Locatelli et al., 1999) in-dicate that Pb pollution of water is a widespread phenomenon, probably ascribableto atmospheric pollution rather than to local inputs.

4. Conclusions

Heavy metals in algae from the southern basin of the Lagoon of Venice are partiallycomparable to those in other areas of the lagoon.

Particularly, Cr concentrations are lower than expected based on the higherCr levels in the sediments of the southern basin reported in the literature. Thisfact contributes towards an understanding of the risk of transferring Cr from thesediments to the water.

The widespread presence of Pb peaks in May supports the hypothesis that at-mospheric inputs, due to the rainy season, largely contribute to determine Pb inputsto the lagoon.

Final conclusions on metal biomonitoring in this area of the lagoon by meansof macroalgae do fit dissolved metal levels measured in water by other authorsworking on the same research project ‘Venice Lagoon Ecosystem Project’, as inprevious studies on the northern basin (Martin et al., 1994). The importance ofmacroalgae as biomonitors of dissolved metals is, therefore, confirmed.

Acknowledgements

Grateful thanks are due to Prof. V. Albergoni, for giving me the opportunity ofcollaborating in the ‘Venice Lagoon Ecosystem Project’, Prof. C. Tolomio for de-fining the taxonomy of studied species, Dr. L. Pivotti for guiding and assisting usin collecting samples, Mr. F. Cattalini for precious technical assistance in metal de-terminations by atomic absorption spectrophotometer. This research was supportedby a UNESCO-MURST grant for the ‘Venice Lagoon Ecosystem Project’.


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