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Unit 4

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Lesson Plan 2




toxin: poisonous
pollution: contamination of air, soil or water by the discharge of harmful substances
industrial wastes: waste products produced by factories and other industries that often contain harmful chemicals
DDT (Dichloro Diphenyl Trichloroethane): a colorless insecticide, toxic to humans and animals when swallowed or absorbed through the skin
bioaccumulation: toxins building up in each organism as they eat animals in the food web who have already eaten a toxin.


Pollution comes from many sources. It is more difficult to control when it is in water because water itself is a common solvent for many things and transfers pollutants throughout the ecosystem. Southern California has many problems with pollution in the marine environment.

There are many types of pollution, some of the worst are DDT and PCBs (polychlorinated biphenyls--used as insulation in the 1970's). Industrial wastes pollute wetlands, bays, estuaries, and the ocean itself.

Pollutants enter the marine ecosystem in a variety of ways. Until the 1960's some chemicals were allowed to be disposed of off-shore; we did not know then about their long-term toxic effects. Today urban street runoff, farm fields and industrial sites contribute to the toxins in the ocean. Some, such as mercury, which is spewed out by coal burning power plants, fall from the air.

Another important way pollutants enter the marine ecosystem is through sewage plants (outfall sites). They impact the environment through the effects at the outflow site (where the final treatment is deposited into the ocean). Soft, muddy sediments are like sponges that slowly soak up all of the chemicals and toxins. Small animals that live in the sediment pick up tiny particles of it and are then eaten by larger animals. Poisons are then spread throughout the food web. Southern California's Hyperian Sewage Plant is unfortunately a very good example. DDT has been found in the sludge from the Hyperian outfall site. It was thought that by depositing the sludge far out in the bay that the ocean would dilute and cleanse the outfall, but this did not happen.

Benthic (bottom dwelling) animals that live in the soft muddy sediment take the toxins and chemicals into their system, by eating the particles or through taking in the water with the dissolved contaminants. For example, on Catalina Island mussels have been found to contain arsenic. Small fish eat small animals and crustaceans in the sediment. Bigger fish such as the white croaker and California Halibut, eat these smaller fish as well as crustaceans who have already been contaminated. Essentially, fish that eat bottom-dwelling organisms become contaminated over time, as do the bigger fish who eat those fish.

Fish-eating birds and mammals also then become contaminated. Brown pelicans were nearly wiped out along the West Coast because they ate anchovies and other fish contaminated by DDT that flowed into waters off Palos Verdes from a pesticide plant. Scientist say that the DDT that destroyed the egg shells of the bald eagles and led to their extinction on Catalina Island, is related to the DDT in the San Pedro Channel. Years later after DDT had been outlawed, bald eagles were reintroduced to Catalina Island but once again they began to die out. It was discovered that the eagles were eating the seagulls' chicks and eggs who eat the fish which have levels of DDT in them. So although DDT was no longer being put into the San Pedro channel it was still present in the food causing the new group of eagles to have problems in hatching their young.

Dolphins in the San Pedro Channel have higher levels of toxins in them than dolphins found elsewhere. In general dolphins and seals off of Los Angeles County remain highly contaminated. They may grow tumors or lose their ability to fight off disease.

DDT (and other toxins that bioaccumluate) never leaves the system of an organism. Every time an animal is eaten by another animal the DDT or other toxin goes into the new animal and becomes even more concentrated, because the bigger the animal, the more contaminated food they will eat. It is important to note that people are not immune to this problem. People can get very sick from eating tainted fish or shellfish. These toxins can cause cancer or birth defects.