Abiotic Degradation: prominent abiotic degradative processes occur due to the influences of light (photolysis) and water (hydrolysis).
Photolysis – Light, primarily in the ultraviolet range, has the potential to break chemical bonds and thus can contribute significantly to the degradation of some chemicals. Photolysis is most likely to occur in the atmosphere or surface waters where light intensity is greatest.
Hydrolysis – Water, often in combination with light energy or heat, can break chemical bonds. Hydrolytic reactions commonly result in the insertion of an oxygen atom into the molecule with the commensurate loss of some component of the molecule.
Biotic Degradation: Environmental degradationof chemical contaminants can occur at greatly accelerated rates through the action ofmicroorganisms. Microorganisms (primarily bacteria and fungi) degrade chemicals in n effort to derive energy from these sources. These biotic degradative processes are enzyme mediated and typically occur at rates that far exceed abiotic degradation. Biotic degradative processes can lead to complete mineralization of chemicals to water, carbondioxide, and basic inorganic constituents. The process by which microorganisms are used to facilitate the removal of environmental contaminants is called bioremediation.
Bioaccumulation is defined as the processby which organisms accumulate chemicals both directly from the abiotic environment (i.e., water, air, soil) and from dietary sources (trophic transfer). Environmental chemicals are largely taken up by organisms by passive diffusion. Primary sites of uptake include membranes of the lungs, gills, and gastrointestinal tract. While integument (skin) and associated structures (scales, feathers, fur, etc.) provide a protective barrier against many environmental Toxins
Chronic Toxicity: Chronic toxicity is defined as toxicity elicited as a result of long-term exposure to a toxicant. Sublethal end points are generally associated with chronic toxicity. These include reproductive, immune, endocrine, and developmental dysfunction.
Environmental Contaminants and Disease among Marine Mammals.
Massive mortality have occurred over the past 20 years among populations of harbor seals, bottlenose dolphins, and other marine mammals worldwide. In many instances this mortality has been attributed to disease. For example, nearly 18,000 harbor seals died in the North, Irish, and Baltic seas in the late 1980s due to phocine distemper virus. Incidences of the disease outbreak were highest in areas containing high levels ofpollutants, and seals that succumbed to the disease were found to have high tissue levels of polychlorinated biphenyls (PCBs).