Marine pollution refers to a range of threats from land-based sources, and it generally involves contamination of bodies of water such as rivers, streams and oceans. Major causes of marine pollution include oil spills, untreated sewage, marine litter, radioactive substances, heavy metals from mine tailings, persistent organic pollutants, eutrophication and heavy siltation. It also encompasses overfishing and marine habitat destruction.
Oil spills and discharges, industrial discharges and heavy metal emission significantly contribute to marine pollution. Moreover, the discharge of untreated sewage in areas near the shore spreads tremendous amounts of contaminants into the ocean and coastal zones. These human activities severely damage marine life. Wastewater discharged into the sea is hazardous to coral reefs and marine animals.
Agricultural run-off, especially Nitrogen, are heavily discharged into rivers and are eventually carried to oceans. This presents a serious threat to marine ecosystems and also human health. Common man-made pollutants that contaminate the ocean include sewage, oil, chemical fertilizers, pesticides, herbicides, detergents and plastics. Most of these pollutants accumulate at the depths of oceans and are ingested by small marine organisms, thereby entering the global food chain. Plastics, which are typically disintegrated and consumed by fish, are hazardous to marine animals and the people eat the contaminated fish.