Evaluation of surficial sediment toxicity and sediment physico-chemical characteristics of representative sites in the Lagoon of Venice (Italy)

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Abstract

Toxic hazard in sites with varying types and levels of contamination in the Lagoon of Venice was estimated by means of toxicity bioassays based on the early life-stages of the autochthonous sea urchin Paracentrotus lividus. Elutriate was chosen as the test matrix, due to its ability to highlight potential toxic effects towards sensitive biological components of the water column caused by sediment resuspension phenomena affecting the Lagoon. Surficial sediments (core–top 5 cm deep), directly influenced by resuspension/redeposition processes, and core sediments (core 20 cm deep), recording time-mediated contamination, were sampled in some sites located in the lagoonal area most greatly influenced by anthropogenic activities. Particle size, organic matter and water content were also analysed. In two sites, the results of physical parameters showed that the core–top sediments were coarser than the 20-cm core sediments. Sperm cell toxicity test results showed the negligible acute toxicity of elutriates from all investigated sites. The embryo toxicity test demonstrated a short-term chronic toxicity gradient for elutriates from the 20-cm core sediments, in general agreement both with the expected contamination gradient and with results of the Microtox® solid-phase test. Elutriates of the core–top 5-cm sediments revealed a totally inverted gradient, in comparison with that for the 20-cm core sediments, and the presence of a “hot spot” of contamination in the site chosen as a possible reference. Investigations on ammonia and sulphides as possible confounding factors excluded their contribution to this “hot spot”. Integrated physico-chemical and toxicity results on sediments at various depths demonstrated the presence of disturbed sediments in the central basin of the Lagoon of Venice.

Introduction

The lagoon of Venice is a complex system characterized by high macro- and microvariability and by dynamics greatly influenced by anthropogenic activities (Ravera, 2000). A recent monitoring program (Venice Water Authority, 1999) has been carried out to assess the distribution of priority micropollutants in surface sediments, highlighting the presence of heavy metals, hydrocarbons, PAHs, PCBs and PCDD/Fs. A pollution gradient from the Industrial Zone towards the sea inlets was evidenced and pollutant loadings estimated (Critto and Marcomini, 2001). Recent studies have demonstrated that, in the last few decades, several modifications have occurred in hydrodynamics (Melaku Canu et al., 2001) and throphic conditions Sfriso and Marcomini, 1996, Sfriso et al., 2003. High levels of suspended particulate matter were evidenced by remote sensing (Rosselli et al., 2002), particularly in the most highly anthropized central basin of the Lagoon, where other studies have demonstrated that sediment fluxes into the water column have increased by about 4- to 11-fold on a yearly basis Facca et al., 2002, Sfriso et al., 2003. Moreover, since the early 1980s, the introduction and rapid diffusion in the Lagoon of the allochthonous bivalve Tapes philippinarum (Adams and Reeve, 1950) has determined a sharp increase in the number of bivalve fisheries and also illegal fishing (Facca et al., 2002). Exploitation of this resource by means of high impact gears (Pranovi and Giovanardi, 1994) causes increased sediment resuspension. Large quantities of resuspended particulate matter and associated pollutants may have, as direct consequences, redistribution of contaminants and biological effects on the benthic community and water column organisms Orel et al., 2000, Volpi Ghirardini et al., 2003.

Estimating toxic hazard due to sediment contamination by means of toxicity bioassays is valuable, because only “biological instruments” are able to integrate the various complex effects of pollutant mixtures. In the present work, toxicity bioassays based on the early life-stages of the autochthonous sea urchin Paracentrotus lividus (Lamark, 1816) (sperm cell toxicity and embryo toxicity tests) were used to assay elutriates, to assess potential toxic effects due to sediment resuspension.

Sea urchin toxicity bioassays are internationally recognized as reliable, sensitive and ecologically important tools for biomonitoring marine and estuarine environments ICES, 1997, US EPA, 2000 and standard methods are available in some countries Environment Canada, 1992, US EPA, 1994, US EPA, 1995, ASTM, 1995. Toxicity bioassays using gametes and embryos of P. lividus are being studied in some Italian research laboratories by means of several methodologies (Arizzi Novelli et al., 2001). Two tests have been developed for P. lividus with reference to standard procedures, a sperm cell toxicity test (Volpi Ghirardini and Arizzi Novelli, 2001) and an embryo toxicity test (Arizzi Novelli et al., 2002a), both of which have been demonstrated to be reliable, effective predictive and protective biological tools. In addition, on the basis of data available for pure compounds compared with results obtained on other acute and chronic tests, the sperm cell toxicity test may be considered as acute and the embryo toxicity test as short-term chronic. The sensitivity and discriminatory ability of both tests were evaluated using elutriates from sediments in the Lagoon of Venice as test matrices Arizzi Novelli et al., 2002b, Volpi Ghirardini et al., 2004. Sea urchin toxicity tests have been recommended for toxicity assessment of elutriates Environment Canada, 1992, ICES, 1997, Nendza, 2002, and P. lividus male gametes and embryos have been used in previous studies to assess the toxicity of elutriates from sediments both of the historical city centre of Venice Da Ros et al., 1997, McFadzen, 2000 and of other sites (industrial, estuarine and shallow waters) in the Lagoon Volpi Ghirardini et al., 1999, Volpi Ghirardini et al., 2003.

In order to evaluate toxicity by taking into account anthropogenic sediment alteration, two different types of sediment samples were collected: (i) a surficial sediment (5 cm deep), directly influenced by resuspension/redeposition processes, and (ii) a deeper sediment (20 cm deep), recording time-integrated contamination. As contaminant concentrations often correlate with the finest fractions of sediments, physical parameters (grain size, organic matter, water content) were also analyzed. High gradients of sediment contamination in the Lagoon of Venice from the Industrial Zone to the sea inlets (Venice Water Authority, 1999) indicated the most suitable areas for sediment collection. Elutriate was chosen as the matrix for toxicity tests because it is representative of water-extractable components. It is recommended in cases of sediment dredging, resuspension and movement in aquatic environments (US EPA and US ACE, 1998) for its ability to give information on potential effects towards sensitive biological components of the water column, including gametes, embryos and larvae.

In recent years, the occurrence in test matrices (elutriates and particularly porewater) of “confounding factors” (such as ammonia, sulphides) has given rise to frequent “false positives” which may lead to inaccurate conclusions (Lapota et al., 2000). At present, indications for acceptable ranges of ammonia and sulphides in these matrices are not available in the literature (Lapota et al., 2000) and sediment toxicity identification evaluation (TIE) studies have been proposed (Wang and Chapman, 1999). For these reasons, we chose to proceed with caution, investigating potential contributions to the toxicity of ammonia and sulphides, identifying their concentrations in environmental samples, and comparing them with the sensitivity data available for sea urchin methods.

Section snippets

Sediment sampling

Four sampling sites (Fig. 1) covering varying types and levels of contamination were selected in co-ordination with other research groups (Co.Ri.La. Project, Line 3.3. “Efficiency of the lagoon metabolism”) and based on previous data. Three sites (SE, CEL, TR) were located in zones influenced by anthropogenic activities, in shallows characterized by bare substrates. A fourth sampling site (DE) was located in an estuarine area.

One station (SE) was close to the island of Sant'Erasmo, in an area

Sediment characterization

Results of grain size and organic matter analyses, and water content for the two core sediment samples (5 and 20 cm deep) are listed in Table 1, together with the geographical co-ordinates of sites. The table highlights different sedimentological environments for the four sites. Samples from site SE show very similar percentages of sand, silt and clay. Sample CEL-5 shows a larger amount of sandy fraction (65%) compared with sample CEL-20 (51%), taking into account that CEL-20 is a homogenized

Sediment characterization

Results of particle size distribution, volatile organic matter and water contents confirm that sediments from site DE were significantly different from sites located in the open Lagoon, highlighted by the highest clay values and water contents (Table 1). Sediment samples from sites DE and SE did not show any grain size differences between the top 5 cm and top 20 cm. Instead, samples from sites CEL and TR showed a coarser sediment composition in surficial sediment cores (5 cm), indicating

Conclusions

This work aimed at providing evidences of sediment toxicity using acute and short-term chronic tests with sea urchin on elutriates, identifying possible confounding factors of toxicity (such as ammonia and sulphides) and taking into account the physico-chemical characteristics of sediments (particle size, organic matter and water content). Integrated physico-chemical and toxicity results on sediments at different depths demonstrated the presence of disturbed sediments in the central basin of

Acknowledgements

This work was partly funded by the Consorzio Ricerche Laguna (Co.Ri.La.) of Venice (Italy). The authors are very grateful to Emanuele Argese for his kind collaboration and Mario Pistolato for sedigraphic analyses. Gabriel Walton revised the English text.

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