The sensitivity of the freshwater non-indigenous mollusc Dreissena polymorpha towards fluoride (F) toxicity was examined in short-term (96-hr LC50; lethal concentration fifty) and long-term (18 days) laboratory experiments. The results indicate that the species is very resistant to F in water, much more than other aquatic invertebrates. In addition, they indicate a concentration- and time-dependent induction of oxidative stress by F exposure and a consequent alteration of the activities of antioxidant enzymes such as superoxide dismutase and catalase. The activity of both of these enzymes progressively decreased with increase of the exposure period when the F concentration was kept constant. Moreover, the appearance of pyknotic nuclei, as well as positivity to TUNEL analysis (Terminal deoxynucleotidyl transferase dUTP nick end labelling) suggests activation of the apoptotic machinery in tissues of animals exposed to high F concentration. This result appears to be related to a sustained condition of oxidative stress
