DDT is a pesticide that is long lasting and can stay in the environment for years. It was sprayed during WWII to try to erradicate Malaria mosquitoes. It was also used as a pesticide to kill insect pests on crops and in the environment. Unfortunately, due to runoff, it ended up in the water supply and ultimately in rivers, lakes and streams. In food chains and webs, as you proceed from producer, to primary consumer, to secondary consumer, the amount of DDT magnifies as each level progresses. This is known as bioaccumulation. Unfortunately, the bald eagle almost became extinct because of DDT. The prey they ate like fish and small mammals had DDT in their tissues and the presence of DDT weakened the eggshells of their young. DDT has even been traced to humans because the milk had DDT in it, due to the cows feeding on grass, sprayed with pesticides. In Lake Apopka Florida, the effect of DDT has feminized many of the male alligators, and due to this occuring, the levels of the alligator population dropped significiantly. DDT is an endocrine disruptor. It can mimic other hormones in the body, causing males to become feminized, for example. In 1962, the author Rachel Carson wrote the important novel, Silent Spring which highlighted what could occur to the environment if people used these chemicals indiscriminantly. By 1972, the use of DDT was banned in the U.S. and most countries in the world have followed suit. The eagles have rebounded as have other organisms. However, the chemical DDT is still in the environment all of these years later.
DDT kills off insects but also has the nasty habit of affecting larger organisms as it bioaccumulates and biomagnifies going up the food chain. DDT is soluble in lipids and will accumulate in fat. DDT kills by permeabilizing the plasma membranes in insects, impacting nerve function. In birds, it thins eggshells, and eventually the birds will die off. This is what happened to the bald eagles before DDT was banned. People who eat fish in which the DDT has bioaccumulated will accumulate DDT until it poisons them, leading to nausea, tremors and confusion. Ultimately, as DDT is an estrogen mimic, it might cause birth defects and affect children's development. It would take a long time to accumulate and magnify up the food chain, but the bigger animals would eventually die off as well. In the short term, insects would get killed off, beneficial and non-beneficial ones. If too many insects die, there will be no food at the bottom of the food chain, the fish woill be hungry and the people will go hungry as well. DDT use would also lead to the selection of insects immune to the pesticide. So, eventually, the bigger animals would suffer, but the insects would be as strong as ever.