The marine ecosystem consists of seas, oceans and estuaries. Although it is very vast but it interacts with human life in various ways the oceans are used for navigation, fisheries, aquaculture, and acquisition of water, naval and military exercises. It is also used for discharge and dumping of variety of wastes.
The ocean reservoir is continuously subjected to sites of natural fluxes. Once material is delivered to the ocean, it is subjected to transport via marine circulation system. The very vastness of the ocean has led to the assumption that all wastes dumped into them can be harm less observed.
Pollutants derived to the oceans enter the circulation driven transport and biogeochemical driven removal processes, unless degraded are finely deposited in the sediment compartments of the ocean reservoir” and tends to have the greatest impact in coastal and marginal seas.
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Amongst the number of pollutant oil, sewage persistent organic compounds, trace metals and artificial radio-nuclides are considered to be most important. The ever increasing range and volume of polluting activities tend to seriously affect marine production. Marine pollution is most evident in coastal waters and estuarine areas.
Oil is the most important pollutant of the oceans. It is a complex substance which includes any elements of different kinds of organic molecules. The main elements are carbon and hydrogen but nitrogen, oxygen, sulphur and metals such as Nickel and Vanadium are also present, components of petroleum undergo a large number of compositional changes such as evaporation, dispersion, adsorption, emulsification, sedimentation, chemical oxidation and degradation.
Petroleum hydrocarbons enter sea in a variety of ways including run-off, air borne contaminants, and leaks from pipelines, and underground storage tanks. Oil wastes discharged from ship, tankers and refineries have been a major source of pollution especially for beaches. It has been estimated that each liter of spilled oil may cover an area of about 4000 square metres over the water surface. As per estimates from 3 billion tonnes of oil produced per year about 3 million tonnes enter the marine environment each year.
In general, the aliphatic compounds of oils are relatively less toxic while the monohydric compounds ire generally toxic. The degree of toxicity increases with increasing unsaturation. The surface active substances which they contain weak membranes more permeable and thus increase the penetration of toxic compounds in animals.
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When petroleum hydrocarbons enter the environment, a variety of micro-organisms participate in their degradation. It has been found that prior adaptation to hydrocarbons in the environment enhances the subsequent rate of hydrocarbon degradation.
In soils, oil spoils more predominantly in a vertical direction in aquatic environment in a horizontal direction on the water surface. In soils, it becomes more difficult or the volatile water compounds to escape and thus there is increased toxicity risk for the microorganisms.
The effects of both discharges and accidental release of petroleum hydrocarbons have been studies with a wide variety of organisms and biological processes. The physical properties of floating oil are of special threat to higher vertebrates be especially aquatic birds. All animals depend on plankton food directly or indirectly. The oil films inhibit the growth of plankton. Hydrocarbon when incorporated into particular organisms becomes stable. Thus, the oils droplets react the marine products. Which are harvested for human consumption?
Many aspects of oil polluting are still largely unknown. The tremendous burden of pollutants is affecting the health and integrity of the world’s oceans due to oceanic pollution, a 30-40 per cent decline n the overall productivity of pelagic organisms from shrips to whales has been observed in the past 25 fears. When oil covers the rocks and sea weeds, molluscs, growing on them die.
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Many control strategies are being developed and implemented to combat global oil pollution. Better environment awareness and understanding have helped in improving marine water quality.