Molecular biomarkers of oxidative stress in aquatic organisms in relation to toxic environmental pollutants.

The potential of oxygen free radicals and other reactive oxygen species (ROS) to damage tissues and cellular components, called oxidative stress, in biological systems has become a topic of significant interest for environmental toxicology studies. The balance between prooxidant endogenous and exogenous factors (i.e., environmental pollutants) and antioxidant defenses (enzymatic and nonenzymatic) in biological systems can be used to assess toxic effects under stressful environmental conditions, especially oxidative damage induced by different classes of chemical pollutants. The role of these antioxidant systems and their sensitivity can be of great importance in environmental toxicology studies. In the past decade, numerous studies on the effects of oxidative stress caused by some environmental pollutants in terrestrial and aquatic species were published. Increased numbers of agricultural and industrial chemicals are entering the aquatic environment and being taken up into tissues of aquatic organisms. Transition metals, polycyclic aromatic hydrocarbons, organochlorine and organophosphate pesticides, polychlorinated biphenyls, dioxins, and other xenobiotics play important roles in the mechanistic aspects of oxidative damage. Such a diverse array of pollutants stimulate a variety of toxicity mechanisms, such as oxidative damage to membrane lipids, DNA, and proteins and changes to antioxidant enzymes. Although there are considerable gaps in our knowledge of cellular damage, response mechanisms, repair processes, and disease etiology in biological systems, free radical reactions and the production of toxic ROS are known to be responsible for a variety of oxidative damages leading to adverse health effects and diseases. In the past decade, mammalian species were used as models for the study of molecular biomarkers of oxidative stress caused by environmental pollutants to elucidate the mechanisms underlying cellular oxidative damage and to study the adverse effects of some environmental pollutants with oxidative potential in chronic exposure and/or sublethal concentrations. This review summarizes current knowledge and advances in the understanding of such oxidative processes in biological systems. This knowledge is extended to specific applications in aquatic organisms because of their sensitivity to oxidative pollutants, their filtration capacity, and their potential for environmental toxicology studies.