DDT is a neurotoxin. It affects the nerve impulses that tell muscles when to contract and relax. When an organism is poisoned with DDT, it dies by either convulsions (random, uncontrolled contraction of the muscles) or paralysis (total loss of muscle control).

We can measure the amount of DDE or other pollutants found in air or water using the unit ppm, or parts per million. 1 ppm is one part in 1,000,000, like one penny in $10,000.

The lethal concentration of DDE in birds ranges between 35 and 181 ppm.

However, chemicals can have negative effects at levels lower than the lethal concentration. Although these smaller amounts will not kill the adult animal, they can cause damage to the body's nervous system and reproductive system.

Now that you've learned about the environmental science relevant to peregrines, review this timeline of major environmental events from the 20th century to see if you can find a clue about the decline in peregrines.