Within the framework of a Weight of Evidence (WoE) approach, a set of four toxicity bioassays involving the amphipod Corophium volutator (10 d lethality test on whole sediment), the sea urchin Paracentrotus lividus (fertilization and embryo toxicity tests on elutriate) and the pacific oyster Crassostrea gigas (embryo toxicity test on elutriate) was applied to sediments from 10 sampling sites of the Venice Lagoon (Italy). Sediments were collected during three campaigns carried out in May 2004 (spring campaign), October 2004 (autumn campaign) and February 2005 (winter campaign). Toxicity tests were performed on all sediment samples. Sediment grain-size and chemistry were measured during spring and autumn campaigns. This research investigated (i) the ability of toxicity tests in discriminating among sites with different contamination level, (ii) the occurrence of a gradient of effect among sampling sites, (iii) the possible correlation among toxicity tests, sediment chemistry, grain size and organic carbon, and (iv) the possible occurrence of toxicity seasonal variability. Sediment contamination levels were from low to moderate. No acute toxicity toward amphipods was observed, while sea urchin fertilization was affected only in few sites in just a single campaign. Short-term effects on larval development of sea urchin and oyster evidenced a clear spatial trend among sites, with increasing effects along the axis connecting the sea-inlets with the industrial area. The set of bioassays allowed the identification of a spatial gradient of effect, with decreasing toxicity from the industrial area toward the sea-inlets. Multivariate data analysis showed that the malformations of oyster embryos were significantly correlated to the industrial contamination (metals, polynuclear aromatic hydrocarbons, hexachlorobenzene and polychlorinated biphenyls), while sea urchin development to sediment concentrations of As, Cr and organic carbon. Both embryo toxicity tests were significantly affected by high ammonia concentrations found in the elutriates extracted from some mudflat and industrial sediments. No significant temporal variation of the toxicity was observed within the experimental period. Amendments to the set of bioassays, with inclusion of chronic tests, can certainly provide more reliability and consistency to the characterization of the (possible) toxic effects.

The 96-h water-only exposure and 10-d sediment toxicity tests with the amphipod Corophium orientale were performed in order to enhance the knowledge about its overall sensitivity and its applicability to Venice Lagoon sediments. The values obtained with cadmium as reference toxicant demonstrated a certain variability of the LC(50); the higher value was found in spring and the lower in late summer. Tests with other pure chemicals (Ni, Total Ammonia, Sodium Dodecyl-Sulphate) showed good discriminatory power; the toxicity gradient observed was: Cd (LC(50) of 3.3 mg/L)>SDS (LC(50) of 8.7 mg/L)>total ammonia (LC(50) of 126mg/L)>Ni (LC(50) of 352 mg/L). Sediment toxicity test results were used to obtain information on non-treatment factors (grain-size, TOC content) that could act as confounding factors, and to develop a site-specific toxicity-score based on minimum significant difference approach. Confounding factors seem not to affect test results. The procedure to develop the toxicity score took into account the relatively lower sensitivity of C. orientale with respect to other amphipods commonly used in toxicity tests (Ampelisca abdita and Rhepoxynius abronius).

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A toxicity identification evaluation phase-I (TIE-1) procedure was carried out on five pore water samples extracted from sediments of the Venice Lagoon previously investigated to assess both chemical contamination and toxic effects on the biota. Two different sequential TIE procedures were tested. A first sequence (TIE-1) provided for adding Na2S2O3, adding Na-EDTA, filtering, elution through a C18-SPE column and removing ammonia using the macroalgae Ulva rigida Agardh 1823, while a second procedure (TIE-2) was set up using U. rigida treatment for ammonia removal as first step, keeping unchanged the sequence of the other manipulations. Two different exposure time to the macroalgae were tested (3-h and 15-h). Sperm-cell toxicity test with the echinoid Paracentrotus lividus and embryotoxicity tests with the bivalves Mytilus galloprovincialis and Crassostrea gigas were performed on pore-water samples to assess the effect of the sequential treatments on the overall toxicity. The results confirmed that ammonia contribution to toxicity is strong in most of the samples and that metals, specially Cu, are of concern at least in three sites. The TIE-2 procedure provided more reliable results for the samples characterized by high ammonia contribution to the overall toxicity, whereas the results of TIE-1 and TIE-2 were equivalent for the samples where ammonia contribution was not prevailing. Chemical analyses and test results showed that a 3-h U. rigida exposure is suitable to remove ammonia toxicity minimizing potential metal up-take.

A whole-sediment test with the infaunal amphipod Monocorophium insidiosum has been developed to assess the long-term effects exerted by sediment contamination on survival, growth rates and attainment of sexual maturity. Juvenile amphipods were exposed for 28 days to a control sediment (native sediment) and three sediment samples collected in sites of the Venice Lagoon, characterized by contamination levels ranging from low to moderate, and absence of acute toxicity toward amphipods. Growth rate was estimated as daily length (μm d) and weight increments (μg d). The long-term exposure to the test sediments affected significantly both growth rate and attainment of sexual maturity of the females of M. insidiosum. In contrast, survival was high and uniform among all the samples, despite the contamination gradient. The results suggest growth to be the more reliable and statistically relevant endpoint. Attainment of sexual maturity, although allowed the identification of detrimental effects, was affected by a higher among-replicates variance as compared with growth rates, and thus less reliable than growth for the identification of impairments. The significant impairments observed both on growth and attainment of maturity evidenced the need to address the monitoring, also in the Lagoon of Venice, towards the assessment of the long-term effects on benthic species.