Long term exposure to pesticides may result in the gradual accumulation of a lethal dose. Carson cites noted failures to control gypsy moth, fire ants, and elm bark beetle as notable examples. Pesticides may not remain in the area where they are applied. Pesticides applied by air may drift, and those applied to the ground may be washed into streams and lakes. One environmental mishap in Austin, Texas in 1961 resulted in fish kills for several hundred miles downstream.
Persons applying pesticides often apply in heavier rates than labelled rates.
Certification and training of pesticide applicators was not required in the 1950's and 1960's. Few pesticides target one pest. Beneficial insects including pollinators and predators often are eliminated. Pests regularly and predictably develop resistance to chemicals. The first strategy to offset resistance is to increase the amount applied, Eventually, a completely different chemistry must be used.