Integration of biological responses from a suite of bioassays for the Venice Lagoon (Italy) through sediment toxicity index – Part A: Development and comparison of two methodological approaches
Introduction
Toxicity bioassays are routinely employed for sediment quality assessment, in order to estimate possible effects of contamination on living organisms (Chapman et al., 2002). Such toxicity data are often difficult to join into a single response since bioassays involve various phases of exposure, are conducted on a variety of aquatic organisms and consider a lot of endpoints. There is now the need to classify the continuous toxicity response into discrete categories since the European Water Framework Directive (WFD) established five different categories of ecological status for the European water bodies (including marine and coastal waters) according to the degree of anthropogenic alteration (EC Directive 2000/60/EC).
Toxicity indices are intended to synthesize toxicity information translating the results into simple terms for decision-makers, representing them on a common, easily-interpreted scale (Shin and Lam, 2001). Several indices were recently proposed for sediment quality (Wildhaber and Schmitt, 1996, Bombardier and Bermingham, 1999, Shin and Lam, 2001, Mowat and Bundy, 2002, Grapentine et al., 2002, Kiddon et al., 2003), using different mathematical approaches.
This work aims to develop a toxicity index for the Venice lagoon where sediment quality assessment is needed since large amounts of dredged materials are managed and decision-makers would like maximize their reuse in the lagoon for morphological restoration (Apitz et al., 2007). It was estimated that 20 million m3 of material with various levels of contamination will be produced by the dredging activities for the construction of the mobile gates to protect Venice from high tides, for navigation of the Porto Marghera industrial canals and the enlargement of the Port of Chioggia (Apitz et al., 2007).
In this study, a stepwise procedure is followed to select a minimum number of bioassays on suitable matrices in order to integrate their responses into a multimetric toxicity index. This procedure takes its cue from the general one proposed to develop multimetric indices reported by US EPA (2000). The integration of toxicity data is performed using two different approaches: a) starting from the SED-tox index proposed by Bombardier and Bermingham (1999); b) considering the easier concept of the weighted mean, developing the Weighted Average Toxicity Index (WATI).
Finally, this study attempts to evaluate if the developed indices are able to discriminate sediment toxicity among sampling sites characterized by different levels and types of chemical impact.
Section snippets
The stepwise procedure
The stepwise procedure shown in Fig. 1 was adopted.
The first step regards the collection of available toxicity data, with the following requirements: test, test matrix, study site, toxicity data, data quality; reference for data availability.
In the second step, data are selected according to the use of standardized protocols and Quality Assurance/Quality Control criteria for sampling and preparing the matrix and for performing bioassays.
The third step regards the identification of the
Results and discussion
Both indices are applied to the toxicity data concerning 110 sediment samples collected between 1994 and 2005 from 22 sites in the Lagoon, most of which were investigated twice in different seasons. Unfortunately, there are only 52 samples with more than one CM-tox. TEI shows values from 0 to 2.42: 10 samples are classified as toxicity absent, 14 as low, 13 as medium, 10 as high and 5 as very high (Table 4). Samples at very high and high toxicity are from the industrial area of Porto Marghera
Conclusions
Two toxicity indices were developed, according to two different approaches, in order to classify the continuous toxicity responses into five different categories as required by the European Water Framework Directive (Fig. 4). The comparison between the two indices allowed to the following considerations:
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The TEI and the WATI, applied to the available database for the Venice Lagoon, evidence similar responses. Both indices can discriminate among sites with different levels and types of chemical
Acknowledgement
This work was partly funded by the Consorzio Ricerche Laguna (Co.Ri.La.) of Venice (Italy).
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