BURSIAN 77THE EFFECTS OF AGRI-CHEMICALS ON ANIMALSStevenJ.BursianDepartment of Animal Science, M.S.U.East Lansing, MIDomestic animals are raised in environments that can result in exposure to a wide variety ofagricultural chemicals. Because of the desire to maximize agricultural yields, whether related to crops orto food-producing animals, there is extensive use of insecticides, herbicides, fungicides, and otherchemicals to control economically significant pests. Exposure of animals to these types of chemicals maybe intentional, such as the dermal application of various pesticides for control of insect and parasiteinfestation, or exposure may be accidental, such as the consumption of chemically-contaminated feed.In either situation, there are concerns. One concern is the potential deleterious effect of the chemical onthe animal itself.Asecond concern, particularly to producers of food animals, is a commodity, whetherit be meat, milk, or eggs, that is not contaminated with chemicals. While these concerns are not trivial,use of commercial pesticide formulations in accordance with the label, in general, poses minimal risks toanimals and ultimately to the human consumer of food products derived from those animals.However, loss of animals, whether they be domestic or wildlife species, through the use of pesticidesand other agricultural chemicals does occur. For example, the most common causes of poisoning in catsand dogs are insecticides and rodenticides. Insecticides are the second most common cause of poisoningin cattle. When combined with other agricultural chemicals, insecticides, herbicides, and fungicides areamong the most commonly cited sources of chemical toxicity in horses, swine, sheep, and goats. Thisinformation indicates that there are circumstances which can and do result in animal intoxication byagricultural chemicals, particularly pesticides.The primary reason for domestic animal poisoning by pesticides and other agricultural chemicals ishuman error. For example, the miscalculation of concentrations for spraying and dipping procedures andfor oral dosing preparations can result in animals being exposed to a chemical at a concentration severaltimes higher than what it should be. Another common cause of poisoning is the use of insecticides notrecommended for animals or the use of insecticide formulations designed for soil or crop application. Forexample, few of the chlorinated hydrocarbon insecticides are recommended for use on animals becauseof their high toxicity or because of their persistence in tissues. Wettable powders and emulsifiableconcentrates intended for spraying on plants are not suitable for animal application because the particlesize of these formulations is larger than the particle size for animal formulations. Thus, when a plant, preparation is sprayed on an animal or used as a dip, there is a tendency for the heavy particles to78 GENERAL SESSION - ENVIRONMENTAL ISSUESconcentrate on the hair of the animal, resulting in excessive exposure and possible toxicity. The use ofseed grain or other plant components which have been treated with pesticides such as heptachlor foranimal feed has resulted in situations where large numbers of food producing animals have been exposedto toxic and persistent chemicals. The spraying of pesticides on crops or land has resulted in animalexposure either through direct contact with the spray or via consumption of treated vegetation. Improperstorage of chemicals is a common cause of animal poisoning. Granular or powdered pesticideformulations, when stored with feed ingredients, can easily be mistaken for salt or mineral preparationsand, as a result, be inadvertently mixed into animal feeds. Chemicals stored or disposed of in areas whereanimals have access to them is a potential problem because of their indiscriminating eating habits. Placingfeed or water in containers which previously held chemicals can lead to poisoning if the containers arenot properly decontaminated.The previous examples of circumstances in which animals are inappropriately exposed to chemicalsare preventable. The vast majority of pesticide problems in domestic animals results from ignorance ormismanagement. This carelessness can affect a few animals of a single producer or it can impact a wholeindustry.Itis important to realize in the following description of agri-chemical effects on animals that,based on our present knowledge, these effects are not likely to occur in the field if the chemical is usedand stored properly. The effects described are often the results of controlled experiments utilizinglaboratory animals which have been administered doses of the chemical which exceed the concentrationthat an animal is likely to be exposed to in the field.Itis also important to realize that there is aconsiderable degree of uncertainty in using toxicological data obtained in a very controlled and artificiallaboratory situation to predict events in our environment which is considerably less controlled.Of the agricultural chemicals that animals can potentially be exposed to, insecticides are of primaryconcern. This can be attributed to the fact that insecticides can be applied to animals as well as plantsand what makes a chemical toxic to insects can also make it toxic to other species of animals. Theinsecticides most commonly used are the organophosphates and carbamates. Examples of organophos-phorus insecticides include chlorpyrifos (Dursban), isofenphos (Oftanol), trichlorfon (Proxol, Dylox),ethoprophos (Mocap), acephate (Orthene), isazofos (Triumph), and diazinon. Isazofos and diazinon aretwo examples of compounds that have restricted use because of harmful effects in the field which werenot anticipated in the laboratory. Carbamates include carbaryl (Sevin) and bendiocarb (Turcam). Theorganophosphates were introduced as insecticides after World War II and eventually replaced most of theenvironmentally persistent organochlorine insecticides such as DDT. The carbamate carbaryl wasintroduced in 1957 and this class of insecticide has gained in popularity because the carbamates tend tobe less acutely toxic than the organophosphates.Organophosphate and carbamate chemicals have the same mechanism of action and thus have similareffects on animals. In order to understand how these insecticides affect an animal, it is necessary to havea general understanding of how a nerve cell works. A typical nerve cell (Figure 1) is comprised of a cellbody and a single long axon. When