Some major types of pollutants that have been the focus of recent research are oil, sewage, garbage, chemicals, radioactive waste, thermal pollution and also eutrophication.

1. Sewage: This type of pollution is discharged into the oceans all over the world. Sewage adds to the amount of small particles suspended in the water column and contributes large amounts of nutrients. The effect of sewage is difficult to detect on the open coast, but in semi-enclosed areas the effects are devastating. Near sewage outflow areas in temperate waters of California , the benthic invertebrate communities have degraded, kelp beds have disappeared and diseased fish have become more prevalent. In tropical waters, outflows near coral reefs have caused a bloom of algal species that grows over the coral, and eventually smothers them to death.

2. Chemicals: These are toxic substances that are released by the industrialized nations and make their way into ocean systems. They are not visible like garbage and sewage and therefore can sneak their way into ocean systems undetected. Toxic chemicals often enter ocean systems through food chains and affect organisms at different times and places from where they were released. An example of this type of pollution is DDT (Dichlorodiphenyltrichloroethane). DDT was used for years as a pesticide on farms. Later it was found that it does not breakdown, but in fact persists for years; just how long is unknown. This compound is relatively insoluble in water and bonds strongly to particles. Although DDT is not used in the marine environment it enters marine food webs through land runoff, precipitation and dumping. DDT is absorbed by plankton but cannot be metabolized. Since, it is not metabolized it accumulates in the food chain until it reaches the top carnivore, where more drastic effects are seen. For example, in marine birds, DDT interferes with calcium deposition in the eggshells. The eggs shells are extremely thin and therefore easily broken. For more information on toxic chemical effects, check out the copper toxicity answer on the OceanLink website at 3. Radioactive waste: The world's oceans have been a sink for radioactive waste from the production of nuclear weapons and electric power since 1944. Radioactive waste enters the ocean from nuclear weapon testing, the releasing or dumping of wastes from nuclear fuel cycle systems, and nuclear accidents. Dumping of high-level radioactive waste is no longer permitted in the ocean, but dumping of low-level wastes is still permitted. Low-level waste contains less radioactivity per gram than high-level waste. High-level wastes usually have longer half-lives. For example, one common high-level waste that is produced by spent nuclear fuel has a half-life of 24,100 years! It has been suggested that contained nuclear waste should be disposed in the deep sea. So little is known about the deep sea environment or the consequences of containment leakage and failure, that the effects could be devastating.

4 .Thermal pollution : Electrical generating plants along the ocean coastlines use the marine waters for cooling purposes which leads to heated water expelled into the marine environment. Few studies have been done on the effects of thermal pollution on the marine environment. Thermal pollution seems to only effect the communities immediately adjacent to the discharge. Thermal discharge is most noted in the tropical areas, where organisms are near their thermal maximum. For example, mangrove trees in a thermal heated bay no longer reproduce and no new seedlings can be found in the lagoon.

5.  Eutrophication : The release of excess nutrients into coastal waters. Fertilizers used on land are washed into the ocean via rivers and streams. High nutrient concentrations cause phytoplankton blooms such as, red tides, various yellow and green foams, slimes, and slicks. Although algal blooms are natural, a higher frequency of their occurrence in the past twenty years indicates an unhealthy ecosystem. The toxicity of recent blooms are increasing, which can have a direct effect on the organisms that feed on them. Also, phytoplankton naturally contains DMS (dimethyl sulfide) which is released from dead phytoplankton into the atmosphere and can be changed to sulfuric acid to eventually contribute to acid rain.

Ozone depletion brought about by the burning of fossil fuels, such as oil and gasoline, is also thought to be indirectly harmful to whales. This is particularly true in the southern hemisphere where ozone depletion has resulted in increased levels of ultra-violet B radiation (UV-B) reaching the earth's surface. UV-B is known to have significant negative biological effects on phytoplankton, the species of marine algae which form the basis of the marine food chain, and krill, a diet staple for many species of baleen whales. By limiting the consumption of fossil fuels, we can actually help protect the whale's ecosystem by keeping the food chain intact. Greater protection of the world's oceans, seas and rivers is vital to provide a livable habitat for whales and other marine species.

Some methods used to clean-up oil spills in the sea:

1. Dispersants: Oil can be broken down more quickly by spraying dispersants (chemicals) on the oil slick from boats or planes. This method only works on fresh, small oil spills.

2. Booms: A boom has a floating skirt suspended down in the water and a sail holding it above the water line. The floating skirt stops the oil from passing. These are used to prevent oil from entering delicate and protected areas.

3. Slick-lickers: This method uses a belt of oil absorbing material that sucks up the oil from the ocean water. The oil is then squeezed out of the absorbing material into a collecting bin.

Some of the methods used to clean-up oil spills on beaches:

1.High Pressure Water: Spraying water at high pressure, in an attempt to "spray" rocks and flat surfaces clear of oil. The sad fact is that by using this method they are also killing all the plants and animals that may have survived the oil spill.

2.Dispersants: Use chemical agents to break up the oil on the beach.

3.Removal: Dispersants are useless on pebble or sand beaches, because the chemicals are readily washed away, so surface sand or pebbles are physically removed by bulldozers or by hand.

4.Plants: Using cut vegetation or straw to absorb the oil. Sometimes the algae growing on the rocks absorb the oil and can cut off the rock.