br Conclusion B esterases and reproductive parameters

Conclusion B-esterases and reproductive parameters can be used as effect biomarkers of the aquatic contamination with chlorpyrifos. In P. corneus exposed for 14 days to the insecticide, the carboxylesterases determined with p-NFB proved to be the most sensitive biomarker. However, exposure to environmental concentrations showed a decrease in the reproduction ability suggesting that the presence of pesticide in the water could be one of the reasons for which many freshwater mollusc species have become threatened or extinct in the past years.
Acknowledgments This work was supported by Grants from the University of Buenos Aires (20020100100455) We thank L. C. Cacciatore.
Introduction Ecological assessment of water quality is fundamental to the management of surface waters and the protection of aquatic ecosystems. Traditionally, biomonitoring of fresh waters has been based on measures of simvastatin zocor structure, focussing on benthic macroinvertebrates (Rosenberg and Resh, 1993). Various indices exist to quantify changes in community composition and these are often combined in multi-metric indices to improve the chances of detecting adverse ecological effects. Such indices are notoriously unspecific and hence cannot be used for diagnostic purposes of specific pollutants. Identifying indicators of adverse change in ecological systems that can diagnose causal agents is a major challenge in environmental risk assessment (Baird and Burton, 2001). Although diagnostic measures have been demonstrated for communities impacted by organic pollution (e.g. saprobity indices, BMWP scores; Ruse, 1996, Wu, 1999, Zamora-Muñoz and Alba-Tercedor, 1996), acidification (e.g. Acid Index and Acid Class; Sandin et al., 2004) or flow modification (e.g. LIFE scores; Attrill et al., 1996, Extence et al., 1999), there are no reliable indicators of ecological impairment caused by contaminants (Baird and Burton, 2001). Furthermore, these indices can respond to disturbances other than those they were developed to detect, making diagnosis of the actual disturbance more difficult. The integrated use of chemical analyses, biochemical and cellular responses to pollutants is considered to be one of the best procedures for detecting impacts of contaminants on aquatic systems (Walker and Livingstone, 1992, Fernandes et al., 2002). Therefore, studying contaminant levels and biochemical effects in key benthic macroinvertebrate species can be a reliable method to diagnose ecological impairment due to contaminants. In general, long-term exposure of living organisms to contaminants results primarily in their accumulation in organs and tissues and secondly in irreversible molecular alterations due to their continuous deleterious action. A general pathway of toxicity induced by many chemical contaminants (quinones, nitroaromatic compounds, polychlorinated biphenyls (PCBs), Orbea et al., 2002, Winston and Di Giulio, 1991; transition metals, Stohs and Bagghi, 1995), is related to their capacity for catalyzing oxidative reactions, leading to the production of reactive oxygen species (ROS) causing oxidative stress. These ROS include superoxide anion radical (O2−), hydrogen peroxide (H2O2) and the highly reactive hydroxyl radical (OH). Of particular interest are transition metals like iron (Fe), copper (Cu), chromium (Cr) and vanadium (V) that through the Fenton reaction are able to facilitate the conversion of superoxide anion to the highly reactive hydroxyl radical. Other metals including cadmium (Cd), nickel (Ni), lead (Pb) and mercury (Hg) may also produce oxidative stress indirectly, depleting glutathione levels or via metal-induced displacement of redox metal ions (Stohs and Bagghi, 1995). To minimize oxidative damage to cellular components, organisms have developed antioxidant defenses. Important antioxidant enzymes are the enzymes superoxide dismutase (SOD, EC 1.15.1.1 converts O2− to H2O2), catalase (CAT; EC 1.11.1.6 – reduces H2O2 to water) and glutathione peroxidase (EC 1.11.1.9 – detoxifies H2O2 or organic hydroperoxides produced, e.g., by lipid peroxidation) (Di Giulio et al., 1995, Halliwell and Gutteridge, 1999). Glutathione S-transferases (GST; EC 2.5.1.18) catalyses the conjugation of glutathione (GSH) with various electrophilic substances, and play a role preventing oxidative damage by conjugating breakdown products of lipid peroxides to GSH (Ketterer et al., 1983). Some GST isozymes in insects also display peroxidase activity (Ahmad, 1992).