Evaluation of nonylphenol toxicity in the clam Tapes philippinarum

Nonylphenol (NP) is widely used in nonionic surfactant formulation, especially in producing nonylphenol ethoxylates (NPEs). NPEs are commonly employed in plastics, latex paints, lubricating oils, emulsifi ers, pesticides, paper and textile industries, and both household and industrial detergents. As a consequence of their wide use, high levels of NPEs are discharged in the aquatic environment, either directly from untreated effl uents or indirectly from sewage treatment plants, where they are biologically degraded to de-ethoxylated intermediates, of which NP is the fi nal product. In water, NP is more persistent than NPEs; moreover, because of its high lipophilicity NP can rapidly be accumulated by aquatic organisms, especially by bivalve molluscs. In the present study, we evaluated lethal and sublethal effects of NP on the clam Tapes philippinarum, ecologically and commercially important in the lagoon of Venice. In 96 hour lethality test, animals were exposed to 0, 0 plus acetone, 0.19, 0.38, 0.75, 1.5, 3 mg NP l-1. The 96-h LC50 was 1.12 mg l-1. To evaluate alterations of physiological responses (fi ltration rate, respiration rate, scope for growth and survival in air) clams were exposed to various sublethal NP concentrations (0, 0 plus acetone, 0.025, 0.05, 0.1, 0.2 mg NP l-1) for seven days. Adverse effects of NP were observed on physiological parameters of clams. Filtration rate signifi cantly decreased at 0.1 and 0.2 mg NP l-1 (p<0.001 and p<0.01, respectively). A signifi cant decrease in respiration rate was also observed at all tested NP concentrations. Moreover, scope for growth, which represents the difference between the energy absorbed from food and the energy lost via respiration processes, was signifi cantly reduced at 0.1 and 0.2 mg NP l-1 (p<0.01 and p<0.05, respectively). Finally, the highest tested NP concentrations signifi cantly decreased the resistance of clams to air exposure and enhanced the mortality rate (P<0.01 at 0.1 mg NP l-1 and P<0.001 0.2 mg NP l-1 ). The results of this study demonstrate that the analysed physiological parameters are responsive to NP short-term exposure. Moreover, as tested NP concentrations are similar to environmentally realistic levels, a condition of potential risk for the preservation of coastal biocenoses is highlighted.