ABSTRACT
In the previous chapters there have been many examples of environmental chemicals, both natural and human-made, that have harmful effects on the nervous system of animals. Many of these compounds are toxic both to vertebrates and invertebrates. Interestingly, ve major groups of insecticides, organochlorine insecticides (OCs), organophosphorous insecticides (OPs), carbamate insecticides, pyrethroids, and neonicotinoids, all owe their insecticidal toxicity largely or entirely to their action on sites in the nervous system. A few of these compounds have also been used to control vertebrate pests (e.g., the cyclodiene endrin has been used for vole control, and the OP insecticides fenthion and parathion for controlling birds). Separate chapters have been devoted to the OCs (Chapter 5), OPs and carbamates (Chapter 10), and the pyrethroids (Chapter 12). Other human-made pollutants also have harmful effects on the nervous system of animals, although they are not used with the intention of doing so. Examples include the organomercury fungicides and tetraethyl lead, which has been used as an antiknock in petrol (both in Chapter 8). It would appear, therefore, that the nervous system represents an “Achilles heel” within both vertebrates and invertebrates when it comes to the toxic action of chemicals. When pesticide manufacturers have screened for insecticidal activity across a wide diversity of organic chemicals, many of the substances that have proved successful in subsequent commercial development have been neurotoxic.
