Rating somewhere between 3 to 4.  Published in 1962 Rachel Carson documents the environmental issues with use of insecticides and pesticides, in particular the chlorinated chemicals such as DDT. Many of the issues were known and published but buried in scientific journals and government documents.  At times heavy on science but she does a good job of bringing awareness of the issues to the general public who then pressured Congress to act.  She writes in an easy to understand style.  These chemicals were used heavily in the US and globally.  Many times the insects targeted were not eradicated.  Birds, fish, animals and humans (farmers, gardens, general population) were all subject to side effects including death.  I can't image reading this in the 1960s when most of this wasn't known by the general public.