Organophosphates and carbamates work by inhibiting the enzyme acetylcholine esterase, which is necessary for normal nerve function. Organophosphates have high toxicity to both birds and mammals and these pesticides have been responsible for thousands of documented bird kills. Birds and other animals can be killed or exposed to pesticides by direct ingestion of pesticide granules, by ingestion of pesticide residues from feathers or fur during preening or grooming, by eating treated plants or insects, or by scavenging carcasses of animals already dead from pesticide exposure. Pesticides can also have less dramatic and noticeable effects, which may eventually result in death. Pesticides can interfere with the ability of parents to care for young, cause disorientation that may lead to increased predation, depress normal immune system function making those exposed more susceptible to disease, and, as mentioned previously, disrupt the endocrine system.
Pesticides are never safe and often have far reaching and unintended effects.
For example, most rodenticides cannot discriminate between rodents and other non target animals, including domestic pets. Pesticide use can affect the ecosystem as a whole. Aquatic invertebrates are extremely sensitive to many pesticides. Since they are near the bottom of the food chain in many wetland, estuarine, and marine ecosystems, their deaths mean less food is available for other animals in these environments. The use of insecticides has lead to the scarcity of bees and other pollinator insects in some agricultural areas.