Final answer:
DDT sprayed on plants biomagnifies as it moves up the food chain, leading to higher concentrations in top predators such as humans and causing ecological harm. This disruption affected bird population sizes and eggshell formations due to the high persistence of DDT in the environment.
Step-by-step explanation:
The phenomenon of DDT being sprayed in minute amounts on food plants and then detected in high concentrations in humans is known as biomagnification. This occurs because the chemical, due to its persistent nature and resistance to breakdown in the environment, accumulates in the tissues of organisms. When smaller animals that contain DDT are eaten by larger predators, the concentration of DDT increases at each successive level of the food chain.
For example, plants sprayed with DDT might be consumed by insects, which are then eaten by small fish. These small fish might be prey for larger fish, which could then be eaten by birds or humans. By the time DDT reaches the top predators, the concentration has greatly increased. This is especially problematic for carnivores at the top of food chains because high levels of chlorinated hydrocarbons like DDT can interfere with the formation of eggshells, making them brittle and causing declines in population sizes of these species.
The widespread and indiscriminate application of DDT led to environmental and health concerns, with significant impacts on wildlife, as documented in Rachel Carson's influential book Silent Spring. It's important to note that biomagnification is not exclusive to DDT but can also apply to other persistent pollutants such as PCBs.