Final answer:
DDT reaches lizards and predatory birds through biomagnification, accumulating in higher concentrations as it moves up the food chain from plants to insects to lizards and finally to birds, leading to weakened eggshells in birds and population declines.
Step-by-step explanation:
The toxin DDT can reach lizards and predatory birds through a process known as biomagnification, which occurs when a substance like DDT accumulates in the bodies of organisms across different trophic levels of a food chain. When insects consume plants sprayed with DDT, they absorb the chemical. Lizards, which may eat these insects, then accumulate higher concentrations of the toxin in their bodies. Predatory birds, in turn, eat the lizards and thus the concentration of DDT accumulates even further in their system. This high concentration of DDT leads to the weakening of bird eggshells, making them susceptible to shattering. As such, even though the birds are not directly exposed to DDT, they are affected due to their position at the top of the food chain.
The catastrophic impact of DDT on wildlife, particularly predatory birds such as eagles, was highlighted in Rachel Carson's 'Silent Spring', and the persistence of the chemical in the environment led to a ban on its use in many countries, including the United States in 1972. Before its ban, the use of DDT had unintended consequences, causing a sharp decline in the populations of birds of prey. Once the ban was put into place, there was a noticeable recovery of these affected bird populations.