Pesticides like many other groups of chemicals can be segregated into families based upon their chemical makeup and characteristics including toxicity (photo 8.4). Common pesticide families are organophosphates carbamates chlorophenols and organochlorines. Organophosphates are derivatives of phosphoric acid and are acutely toxic but are not enduring (Photo 8.5). They are generally known as all insecticides which contain phosphorus. The chemical formulas of the organophosphates contain carbon hydrogen phosphorus and at least one sulfur atom and some may contain at least one nitrogen atom. Organophosphates break down rapidly in the environment and do not accumulate in the tissues. They are generally much more toxic to vertebrates than other classes of insecticides and are therefore associated with more human poisonings than any other pesticide (Table 8.11). They are also closely related to some of the most potent nerve agents including sarin and VX. Organophosphates function by overstimulating and then inhibiting neural transmission primarily in the nervous respiratory and circulatory systems. Signs and symptoms of exposure include pinpoint pupils blurred vision tearing salivation and sweating. Pulse rate will decrease and breathing will become labored. Intestines and bladder may evacuate their contents. Muscles will become weak and uncomfortable. Additional symptoms include headache dizziness muscle twitching tremor or nausea. Examples of organophosphate pesticides include malathion methyl parathion thimete counter lorisban and dursban (Figure 8.18).