ABSTRACT
Many heavy metals such as lead and mercury may also harm the nervous system. It is not surprising that most insecticides are nerve poisons. They have LD50 values in mammals between 1 and 1000 mg/kg.
The structure and functional elements of the nervous system in different animals are quite different, and some selectivity between animals from different groups is expected. On the contrary, various types of nerve cells have a rather
similar general anatomy and chemical organization in widely different animals. We may therefore expect that nerve poisons used as pesticides seldom are very selective between animals, and may harm nontarget insects, earthworms, vertebrates, and birds as much as the pest itself. In spite of this, selective poisons are developed. The selectivity is often based on differences between organisms in uptake, distribution, and detoxication or bioactivation, but finer structural differences in the receptor sites for the poisons may make a big difference in sensitivity between various animal taxa. Cartap owes much of its selectivity to difference in bioactivation to the toxic agent, nereistoxin, whereas the neonicotinoids are selective due to differences in the nicotinic acetylcholine receptor sites in insects and mammals. The pyrethroids are selective mainly due to differences in uptake and distribution.
