She warned the public about DDT & pesticides. When the book initially came out Monsanto discredited her claims to a large extent. (Copy from wiki below) ⬇️

Fierce opposition my left foot… Monsanto was brutal.

In the late 1950s, Carson began to work on environmental conservation, especially environmental problems that she believed were caused by synthetic pesticides. The result of her research was Silent Spring, which brought environmental concerns to the American public. The book was met with fierce opposition by chemical companies, but it swayed public opinion and led to a reversal in U.S. pesticide policy, a nationwide ban on DDT for agricultural uses,[2] and an environmental movement that led to the creation of the U.S. Environmental Protection Agency.[3][4]

In 2006, Silent Spring was named one of the 25 greatest science books of all time by the editors of Discover magazine.[5]