Elsevier

Chemosphere

Volume 47, Issue 4, April 2002, Pages 443-454
Chemosphere

Heavy metal contamination in the seaweeds of the Venice lagoon

https://doi.org/10.1016/S0045-6535(01)00292-2Get rights and content

Abstract

The concentrations of heavy metals (Fe, Zn, Cu, Cd, Ni, Pb, Cr, As) were determined in seven seaweeds of environmental and commercial relevance (Ulva rigida C. Ag., Gracilaria gracilis (Stackhouse) Steentoft, L. Irvine and Farnham, Porphyra leucosticta Thuret, Grateloupia doryphora (Montagne) Howe., Undaria pinnatifida (Harv.) Suringar, Fucus virsoides J. Agardh, Cystoseira barbata (Good. et Wood.) Ag.) collected in four sampling sites in the lagoon of Venice, in spring and autumn 1999. Metals were extracted using hot concentrated acids in a Microwave Digestion Rotor and analysed by absorption spectrophotometry using a flame mode for Fe and Zn and a graphite furnace for Pb, Cr, Cd, Cu, Ni and As. High contamination levels, especially for Pb, were detected in Ulva and to a lesser extent in Gracilaria. Brown seaweeds, especially Cystoseira was highly contaminated by As. The least contaminated genera with all metals except As were Porphyra and Undaria. A concentration decrease for Zn and Cd was observed from the inner parts of the central lagoon, close to the industrial district, towards the lagoon openings to the sea.

Introduction

The use of seaweeds as animal and human food, soil manure, salt extractions (soda, iodine, etc.), colloid production (agar, alginates, carrageenan, furcellaran, etc.), cosmetics, pharmaceuticals, energy production is a very old and widespread practice (Chapman and Chapman, 1980; Bird and Benson, 1987; Bressan and De Luca, 1987; COST 48, 1989 and references therein, Bradford and Bradford, 1996). Seaweeds represent an important economical resource mostly in the Indian and Pacific countries where they are not only largely harvested but also intensively and largely employed in the human nutrition.

In Europe the collection and utilization of seaweeds have a lower diffusion than in the Indian and Pacific areas. Except for the extraction of iodine and soda from fucoids, which has been practiced since the 17th century, and the use of fresh seaweeds as fodder for sheep, cattle and horses, which browse on the shore in some northern countries (Scotland, Norway, Iceland, etc.), the attention to seaweeds has been drawn mostly after the Second World War. The excessive growth of some species (especially Ulva, Enteromorpha, Chaetomorpha, Cladophora, Gracilaria, etc.), which colonized many lagoons and shallow coastal areas, created serious problems for the environment quality, the local populations and economies (Casabianca-Chassany, 1984, Casabianca-Chassany, 1989; Sfriso et al., 1987, Sfriso et al., 1992; Schramm, 1991; Schramm and Nienhuis, 1996 and references therein; Briand, 1991; CEVA, 1993; Menesguen and Piriou, 1995; Morand and Briand, 1996; Sfriso and Marcomini, 1996; Viaroli et al., 1992, Viaroli et al., 1994; etc.). In these areas seaweeds are mainly harvested to prevent or mitigate the effects of an abnormal biomass proliferation and possible anoxic events. However, in European countries the collected biomass is more a problem than a profit. As a consequence, many seaweed studies and projects have been addressed to the biomass conversion and digestion (COST 48, 1987 and references therein; Croatto, 1982; Morand et al., 1990, Morand et al., 1991; Cuomo et al., 1993, Cuomo et al., 1995; Orlandini, 1994; Morand and Briand, 1996).

Another actual European application of seaweeds deals with the environmental monitoring and restoration. Some seaweeds are used or indicated as appropriate biomonitors to study the environment contamination (Munda, 1982; COST 48, 1987; Munda and Hundnik, 1991 and references therein; Marcomini et al., 1993; Haritonidis and Malea, 1995, Haritonidis and Malea, 1999; Sfriso et al., 1995; Malea and Haritonidis, 1999a, Malea and Haritonidis, 1999b, Malea and Haritonidis, 2000). Seaweed crop is also used for nutrient and contaminant abatement (Croatto, 1982; COST 48, 1987 and references therein; Morand and Briand, 1996).

The lagoon of Venice, is the widest shallow area populated by macrophytes, in Italy. Starting from the 60s, the lagoon has been affected by an abnormal production of nitrophilic species, especially Ulva rigida C. Ag., which caused a change in the benthic-flora structure (Sfriso, 1987), the alteration of the nutrient cycles and the occurrence of dystrophic crises (Sfriso et al., 1992). In the 1970's and 1980's, in the central basin, about a third of the entire lagoon, a gross seaweed production of ten million tonnes was estimated (Sfriso and Marcomini, 1994). Since the late 1980's, to prevent the effects of this abnormal biomass proliferation and decomposition, the local administration provided for the seaweed biomass to be harvested (up to ∼55.000 m3 yr−1). Many projects explored the use of seaweed crops in agriculture, in the production of compost and biogas without obtaining economically satisfactory results (Croatto, 1982; Cuomo et al., 1993, Cuomo et al., 1995). Finally, a method for converting the biomass in paper pulp, after a suitable pre-treatment, to produce the “Ulva carta” has been developed from a local paper company, thus solving the problem of the macrophyte crops in an economically convenient way.

Since 1990 a new trend emerged: a strong reduction of Ulva distribution and production was coupled with a re-population of native seagrass and seaweed species. At the same time new seaweeds of eastern origin entered the lagoon of Venice through fishing and commercial traffic. Among these the hard-bottom species: Sargassum muticum (Yendo) Fensholt, Undaria pinnatifida (Harvey) Suringar and Grateloupia doryphora (Montagne) Howe spread over the whole lagoon, while Cystoseira barbata (Good. et Woodw.), a species very common before the Ulva proliferation, re-colonized some areas.

At present, the Venice lagoon is populated by over 250 seaweed taxa differently spread and distributed in the inner and outer littorals. Many of these have a possible economic relevance or can be used as biomonitors for waters (Levine, 1984, Phillips, 1995, Moy and Walday, 1996 and references therein; Haritonidis and Malea, 1995, Haritonidis and Malea, 1999; Malea and Haritonidis, 1999a, Malea and Haritonidis, 1999b, Malea and Haritonidis, 2000), especially for dissolved heavy metal contamination (Rönnberg et al., 1990; Ganesan et al., 1991; Kureishy, 1991; Rajendran et al., 1993, Rainbow and Phillips, 1993; Tariq et al., 1993; Karez et al., 1994; Küçüksezgin and Balci, 1994; Rainbow, 1995; Riget et al., 1995; Leal et al., 1997).

The objective of this paper is to investigate on the contamination level and the capacity of some highly widespread seaweeds growing in the Venice lagoon (viz. Ulva rigida C. Ag., Gracolaria gracilis, Grateloupia doryphora (Montagne) Howe, Porphyra leucosticta Thuret, Fucus virsoides J. Ag., Undaria pinnatifida (Harvey) Suringar, Cystoseira barbata (Good, et Woodw.) Ag.) to selectively accumulate inorganic contaminants: Fe, Zn, Cu, Cd, Ni, Pb, Cr, As. These species were selected for their abundance, biomonitoring capacity and actual (paper pulp making, gas production, soil amendment) and potential uses (as nutrient and contaminant traps, for the extraction of phycocolloids, agar and alginate, and use in cosmetics, pharmacology and animal or human nutrition (Bressan and De Luca, 1987; Penso, 1987, Keiji and Kanji, 1989).

Section snippets

Study area

The lagoon of Venice is a shallow water body with a mean depth of ∼1 m and a total surface of ∼549 km2 (Fig. 1). It is subdivided into three main sections, named the southern, the northern and the central basins. The city of Venice is located in the central basin. The mean tidal excursion is ∼62 cm and the water change is guaranteed by three inlets, which enable the renewal of ≈60% of the lagoon water every 12 h.

The industrial district of Porto Marghera has severely affected the lagoon

Results and discussion

In Table 2 the collected seaweed genera are listed as per sampling station and per session. The seaweeds sampled at Ponte della Libertà were only Ulva and Gracilaria, which are known to be the most pollution-tolerant species among the collected ones. Porphyra, Undaria, are seasonal genera, which were collected in spring only. The contamination level of these genera will be discussed as an indication of spatial variability. Fucus, the species more sensible to eutrophication, was found in the

Conclusions

By these results it is possible to conclude that:

  • 1.

    The heavy metal contamination of the considered seaweed species was in ranges comparable to those reported in the literature for industrialized coastal areas.

  • 2.

    Porphyra and Undaria show the lowest heavy metal contamination. As these seaweeds are seasonal, it is evident that time exposure is a key factor in the metal uptake.

  • 3.

    Ulva exhibited the highest contamination for many of the considered metals, i.e. Fe, Cu, Pb and Cr, and together with Fucus the

Acknowledgements

This work was partly supported by the Consorzio Ricerche Lagunari, (CORILA, Consortium for the coordination of the scientific research on the Lagoon of Venice). The authors are grateful to Mrs. Sonia Ceoldo for technical assistance and to Dr. Orietta Zucchetta for reviewing the English text.

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