A multibiomarker approach to assess environmental pollution in the Lagoon of Venice (Italy). I: the clam Tapes philippinarum as sentinel species.

The aim of the present study was to assess effects of environmental contaminants using a multibiomarker approach in the clam Tapes philippinarum from the Lagoon of Venice. Bivalves were collected in June 2007 in 8 sites of the Lagoon (Campalto, Marghera, Palude del Monte, Valle di Brenta, Cà Roman, San Servolo, Fusina and Canale Dese), differently influenced by both anthropogenic impact and natural conditions. The following biomarkers were chosen: total haemocyte count (THC) and lysozyme-like activity in cell-free haemolymph as immunomarkers, acetylcholinesterase (AChE) activity in gills as a biomarker of exposure to neurotoxic compounds, vitellogenin (Vg)-like protein levels in both digestive gland and cell-free haemolymph as a biomarker of exposure to estrogenic compounds, and survival-in-air widely used to evaluate general stress conditions in clams. The results showed that clams sampled at Marghera and Fusina, near the mainland industrial area of Porto Marghera, had significantly reduced THC values with respect to those of animals from the other sites. Conversely, significantly higher THC was observed in clams from Valle di Brenta and Cà Roman, the former close to the inner border of the Lagoon, influenced by wastewater from agricultural areas, the latter near the lagoon inlet, where intense fishing and passage of ships occur. Significantly increased lysozyme-like activity was recorded in cell-free haemolymph of clams collected at Campalto, influenced by effluents from a sewage treatment plant, Marghera and Cà Roman, suggesting that destabilisation of cell membranes occurred in haemocytes. Lower AChE activity was recorded in gills of clams collected at Fusina and San Servolo, indicating a probable exposure of animals to neurotoxic compounds, which originate from both agricultural and industrial effluent discharge and the urban area of the city of Venice, San Servolo being particularly influenced by municipal effluents from the city. Interestingly, higher Vg-like protein levels were observed in digestive gland and haemolymph of both male and female clams from Campalto, Marghera, Cà Roman, Valle di Brenta and San Servolo. Vg induction is generally recognised as a biomarker of exposure to estrogenic compounds. However, in the light of recent findings concerning involvement of Vg in immune responses (Zhang et al., 2005, Fish Shellfish Immunol., 19: 93-95), evaluation of Vg induction as potential immunomarker in laboratory and field studies is suggested. Significant variations in clam resistance to air exposure were also shown. LT50 values fell from 13 days in clams from Canale Dese, far from urban and industrial sources of pollution, to 6 days in animals collected at Marghera and Fusina, and to 5 days in bivalves from Cà Roman and San Servolo. On the basis of the biomarkers analysed, a homogeneous spatial distribution of contaminants in the Lagoon can be hypothesised, and no hot spot was highlighted. However, clams from less impacted sites in the northern Lagoon, such as Canale Dese and Palude del Monte (the latter used as a licensed area for clam culture), exhibited an overall better condition. For a more exhaustive evaluation of the results obtained, influence of both exogenous (i.e., water temperature and salinity, food availability) and endogenous factors (i.e., reproductive cycle) on functional responses investigated have to be taken into proper account.