Pollutants in the sea sometimes originated from land; they are toxic chemicals that are synthetic, that is, manufactured by humans. Although they are organic, being artificial, they are foreign to many forms of life. One major group of synthetic chemical pollutants are the chlorinated hydrocarbons, used in pesticides to kill insects and to control weeds. Many of these pesticides saved people from diseases and starvation, but they also are harmful tom any other organisms if used unchecked.

Pesticides have not been used directly in the ocean; however, they are very mobile. They are carried by wind, especially when crops are sprayed from planes. They are brought into the ocean from rivers, runoff from land, and domestic sewage. Pesticides are then absorbed by plankton and move up the levels of the food chain. S

ince chlorinated hydrocarbons are synthetic, organisms have not learned a way to break them down; thus, they are nonbiodegradable. Chlorinated carbons are not very soluble in water, persist through many years in the environment and accumulate in fats. Because the pesticides are persistent, the higher an organism is on the food chain, the higher concentration of toxic pesticides are in it. The pesticides are passed from one organism to the next, getting more and more harmful because it cannot be broken down through digestion or by the liver of the animals that eat them. Whales are one of the top carnivores in the ocean; thus, they are very susceptible to biological magnification. Furthermore, chlorinated carbons accumulate in fast, and pups rely on their blubber and their mom's milk (which is made directly from fat) for food. Toxin is passed onto the pups with a weak immunity system in this way. Therefore, many pups die before the age of one.

For each group of 4 students:

• 5 different size beakers,
• water (about 250 mL),
• food coloring,
• a piece of bread,
• construction paper and crayons/colored pencils,
• tape/paste.

• A diagram of the food chain

Creating the animals: This is done by the students in groups of 4.
-Draw the animals on construction papers: algae/plankton, small fish, salmon (medium size fish), herring, whale/shark.
-Color the animals with colored pencils and crayons
-Paste/tape the paper animal on the outside of the beakers. (One animal per beaker).
-Fill the beakers with approximately 50 mL of water. Discussion: This is done with the class as a whole.
-Ask for the definition of a food chain.
-Explain the concepts of a food chain as needed.
-Explain that the beakers represent different organisms in the ocean.
-Ask students to point out members that are the top/bottom of the food chain among the beakers.
-Ask for a definition of toxic chemicals.
-Explain biodegradable vs. nonbiodegradable Main activity:
-Have the students go back into their original groups of 4 and give them food coloring and their set of decorated beakers filled with 50 mL of water.
-Give out instructions as follow:

1. Add one drop of food coloring to all beakers, exposing all animals to the pesticides.
2. Starting with the plankton: what eats the plankton?
3. Small fish eats the plankton, thus concentrating more toxin in itself, demonstrate this by adding one more drop of food coloring ot the small fish beaker.
4. What eats the small fishes?--salmon. Add 2 drops of food coloring to the salmon beaker. (One drop comes from the plankton, the other from the small fish).
5. Continue with the herring. Add 3 drops.
6. With the shark/whale, add 4 drops.
7. Can human eat the top predators of the ocean?
8. Soak the piece of bread into the shark/whale beaker, adding 5 drops of food coloring to the bread, thus concentrate it further.
9. Calculate the amount of toxin humans get if we eat a fish that is at the top of the food chain (how many drops?)
10. Any volunteers to eat the piece of bread?