of natural balance, are called economic poisons. 

 If these poisons occur in food, they may also be 

 considered as adulterants or additives. In addition 

 to the loss in healthy condition, productivity, re- 

 productivity, or death, the producer may suffer 

 further loss through condemnation of meat, milk, 

 or other products before they reach the ultimate 

 consumer. Water, much more than the terrestrial 

 environment, has great mobility and can carry 

 economic poisons and adulterants to areas remote 

 from the origin. It is imperative that drinking 

 water quality be maintained so that intolerable 

 levels of either economic poisons or adulterants 

 in livestock or their products will not occur. Such 

 levels do not necessarily endanger livestock health, 

 it should be noted. 



The problem of accumulated pesticides in ani- 

 mal tissue is complicated by the similarity of patho- 

 logical changes induced by naturally occurring 

 dysfunctions, some of which are not clearly under- 

 stood. Potentiation of toxicity may occur particu- 

 larly in young and old animals as the result. The 

 effects of stress and some dysfunctions related to 

 steroid hormones may cause diseases in poultry 

 which are also induced by organic phosphates. The 

 interplay of arsenic in the phosphorus metabo- 

 lism and the role of copper in phosphorus-molyb- 

 denum interplays indicates the complexity which 

 can be influenced by residues. 



Before 1940, the principal insecticides were 

 compounds of arsenic, lead, lime, sulfur, and fluor- 

 ine. Herbicides included the arsenicals, copper 

 compounds, oils, and chlorates. All of these com- 

 pounds have toxic effects and poisoning continues 

 to be a problem when these materials are handled 

 improperly. Criteria for water, on the other hand, 

 recognize that in the absence of demonstrable 

 disease these compounds should be disregarded. 



Herbicides which contaminate water supplies 

 fall into two general categories: those which afi'ect 

 the metabolism and are toxic to animals, and 

 growth regulators of plants. The most important 

 is probably sodium arsenite which is still used for 

 reasons of economy. Mercurial compounds used as 

 fungicides may occasionally enter water supplies. 

 Pentachlorophenol and various derivatives have 

 wide uses as herbicides, fungicides, and insecti- 

 cides, but apparently the reactivity of these com- 

 pounds in the presence of soil or other organic 

 matter is such that toxicity to livestock in water 

 seldom follows. Sulfur dioxide is a well known 

 general protoplasmic poison, but it is more toxic 

 as a gas than in solution. Herbicides which act 

 as growth regulators in plants, causing derange- 

 ments in plant organization and function, are not 

 usually a threat to livestock. The organic herbi- 



cides are primarily toxicants of plants and usually 

 have little toxic effect on other forms of life. 

 Generally, they are less toxic than the solvents, 

 surfactants, granules, or other adjuvants used in 

 their formulation (151). 



Since 1940, a number of organic insecticides 

 have come into general use. As in the case of 

 inorganic compounds, the action is often directed 

 at some important tissue or metabolic function 

 so that toxicity is influenced by the reactivity of 

 the target tissue as it is in turn acted upon or 

 reacts in the whole organism. The net result of 

 the use of organic insecticides sometimes becomes 

 a race between dosage which will kill and resis- 

 tance of the host which will protect. It is seldom 

 that acute poisoning of livestock is anything but 

 accidental, but today's public attitude is that live- 

 stock water as well as livestock food shall not 

 result in unwholesome residues in meat or other 

 animal products. It may be enough to follow the 

 rule that when the insecticide is used properly, 

 no unusual or long time residue problems will 

 follow. But a much wiser course to follow is to 

 use biodegradable insecticides where possible and 

 to phase out those which have a tendency to 

 accumulate. 



If it is true that the principal action of the 

 organic insecticide is to bring about a derangement 

 of a metabolic pathway or enzyme system, then 

 it follows that under some conditions such anoma- 

 lies may occur naturally. Therefore, the mere pres- 

 ence of an insecticide, such as DDT, in the serum 

 or fat of a diseased animal is not proof that the 

 DDT is responsible for the effect. On the other 

 hand, there is a point beyond which the amount 

 of DDT or other adulterant may not occur with- 

 out representing a threat to health or causing 

 financial loss due to an accumulation in excess of 

 the legal tolerance for the compound. 



Microbiological Pathogens: Water has assumed 

 a major role through the ages in the dissemination 

 of infectious bacteria, protozoa, and vifuses. Man, 

 more than livestock, has profited from knowledge 

 of waterborne diseases. Grazing animals herded 

 on common pastures come in contact with orga- 

 nisms which find in the environment the factors for 

 a complete life cycle. Very few pathogenic micro- 

 organisms can resist desiccation, although some 

 form spores or encyst. Waterborne infections arise 

 through contamination of water supplies, life cy- 

 cles involving a water phase, or through organisms 

 with pathogenic capabilities adapting to growth 

 and reproduction in water. 



Water quality, including pH, mineral, and or- 

 ganic composition, may be very important in 



138 



