While Rachel Carson spends much of Silent Spring explaining the effects of chemicals on the environment, she also details the causes leading to those effects. She especially reveals the harm that nonorganic chemicals used as pesticides wreak on species, particularly certain types of birds—notably America’s national bird, the bald eagle. More specifically, she explains the processes by which eggs are damaged and the accumulated effects of insecticides over time and far along the food chain.
A specific effect of DDT, a chemical commonly used as an insecticide before its 1972 ban in the U.S., was to weaken, and ultimately destroy, the eggs of some birds Carson explains the processes of calcium absorption necessary to proper shell formation. She then details how DDT blocks the absorption so that shells lack the building blocks to form properly. Because the thin shells cannot survive the nesting process, too many babies die and the population declines.
Carson also uses the concept of biomagnification. Even when the animals did not themselves ingest the chemicals, they would be harmed later because they ate plants or other animals that had ingested them. Through biomagnification, the quantity of a given substance in an animal much lower on the food chain is greatly concentrated and continues present in higher levels than in animals higher on the food chain. Thus, the targeting of “harmful” insects (e.g., mosquitoes) through application of pesticides causes a ripple effect by damaging every species that would eat not only those insects but also beneficial ones.