Failure of antioxidant defenses to remove exogenous

Failure of antioxidant defenses to remove exogenous ROS produced by redox cycling chemicals either by being inhibited by those compounds or overwhelmed by an excess ROS, will disrupt the balance between antioxidant/prooxidant system within the organisms leading to oxidative damage (Livingstone, 2003). In this study oxidative tissue damage was evaluated determining lipid peroxidation measured as TBARS (Sohal, 1981, Sukhotin et al., 2002). There was evidence for increased lipid peroxidation measured as TBARS in whole individuals of sites 4, 6, and 7 when compared to less polluted reaches, the exception being organisms collected in site 2 in spring. The presence of illicit chemical discharges from nearby salt mines in site 2 could explain the unexpected high levels of lipid peroxides found in this location. It is worth mentioning that the relatively high levels of lipid peroxides found in individuals collected along the Llobregat river paralleled with altered patterns of antioxidant gaboxadol synthesis (enhanced CAT and/or GST activity for sites 2, 4, 5 and 7; inhibition of GSTPX for site 4 in spring), thus suggesting that an excess of ROS not being removed by the antioxidant defensive systems may have caused an increase in the pro-oxidant status of the organism.
Conclusions In a complex environment affected by many chemical contaminants like the Llobregat River system, toxic interactions between different contaminants and biological systems are likely to be responsible for the observed biological responses. The set of biomarkers used in this and previous studies (Solé et al., 2000, Fernandes et al., 2002) indicate increasing levels of stress in fish and invertebrate species towards downstream reaches or locations nearby industrial and urban areas. For Hydropsyche larvae, increasing levels of metal body burdens and salt in water, enhanced CAT and GST enzymatic activities and lipid peroxidation, in conjunction with new evidence of increasing levels of developmental morphological malformations measured as fluctuating asymmetry (Bonada, 2003) in individuals collected downstream the Llobregat River system, are indicative of increasing levels of stress towards downstream reaches.
Acknowledgements
Introduction Tannery industries produce a large amount of solid and liquid wastes which can impart significant damage to the aquatic environment, as well as, the terrestrial and atmospheric system if not treated adequately. Effluent from a typical tanning unit is usually rich in various organic and inorganic pollutants having high values of suspended solids, chemical and biochemical oxygen demand, ammonia, oil and grease, surfactants and salts like sulfates and chlorides, etc. In addition, the presence of components like sulfides, chromium, chlorinated phenols, azo dyes, cadmium compounds and polychlorinated biphyenls (PCB), etc. turn the effluent more toxic which can potentially damage the aquatic world (Mwinyihija, 2010). Walsh and O’Halloran (1998) investigated on the toxicity of a leather effluent on a population of blue mussels Mytilus edulis in an estuary. While they observed an enhanced growth and condition possibly due to the high nutritive content of the effluent, however lipid peroxidation of digestive glands and amoebocyte proliferation in gills were observed after 1 year of exposure which could be attributed due to fungicide exposure. The ecotoxic potential of tannery wastewater and the associated chromium based components was analyzed by Shakir et al. (2012) employing different bioassays like cytotoxic assay, artemia bioassay and phytotoxicity assay. The results suggested that hexavalent chromium, as well as, the tannery wastewater hold significant environmental damaging potential. Toxicity of tannery effluent in raw, coagulated and biologically treated form was analyzed by Meriç et al. (2005) using sea urchin and microalgal system. The coagulated effluent resulted in higher toxicity than raw effluent in sea urchin embryos and sperm, however the biological treatment improved the effluent quality considerably thus minimizing the environmental damage. The high salinity of tannery wastewater often inhibits the biological treatment, therefore application of salt tolerant mixed microbial consortium have been studied for biodegradation of organics in saline tannery effluent (Sivaprakasam et al., 2008). While the biological treatments are environment friendly, however they often fail to eliminate the recalcitrant pollutants in tannery effluent. A combined process of advanced oxidation or membrane technology with bioprocesses can be an effective solution (Lofrano et al., 2013).