opportunities for copper contamination of water 

 supplies since copper in various forms is widely 

 used in agriculture. One reference indicates that 

 levels of about 160 mg/1 copper inhibits water in- 

 take for turkeys whereas 500 to 600 mg/1 is 

 "harmful" to turkeys when such water is the only 

 drinking water available (67). Even these levels, 

 however, are generally higher than those recom- 

 mended for control of fungus infections in turkeys, 

 suggesting that any damage would be accidental. 



Fluorine may become a ground water contami- 

 nant from underlying strata containing fluorides 

 and may perhaps enter in effluents from certain 

 types of manufacturing processes. The latter, 

 however, are more likely to be airborne than 

 waterborne. The U.S. Public Health Service rec- 

 ommends rejection of drinking water supplies con- 

 taining from 1.4 to 2.4 mg/1, depending on pre- 

 vailing temperatures {175). It is noteworthy that 

 addition of up to 500 mg/1 of fluoride to either 

 the feed or drinking water for cattle did not raise 

 the fluoride level in their milk above 0.5 mg/1 

 (157). 



Iron: Reports on direct toxicity resulting from 

 iron in water are not available. However, it has 

 been suggested that intake of water by livestock 

 may be inhibited if it is high in iron {164). 



Lead may arise as a contaminant of ground 

 waters, both from natural sources (deposits of 

 galena) or as a constituent of various industrial 

 and mining effluents. A complication as far as lead 

 is concerned in livestock waters is caused by the 

 fact that it is a cumulative poison. There is a report 

 of chronic lead poisoning among animals by 0.18 

 mg/1 of lead in soft water {198), and there is 

 fairly general agreement that 0.5 mg/1 of lead is 

 the maximum safe limit in a drinking water supply 

 for animals {129). There is a considerable differ- 

 ence in the relative toxicities of various forms of 

 lead. 



Magnesium: Some salts of magnesium, particu- 

 larly magnesium chloride, may contaminate 

 ground water supplies as a component of waste 

 waters from oil wells, road runoff, and industry. 

 Certain magnesium salts such as the sulfate caused 

 scouring or diarrhea among livestock; however, 

 the level they can tolerate safely appears to be 

 fairly high. It has been reported that livestock 

 will tolerate 2,050 mg/1 of magnesium sulfate 

 in their drinking water without laxative effects 

 (9). 



Manganese: Toxicity data on manganese con- 

 tents in drinking water are not readily available. 

 However, cattle are reported to have suffered no 



serious effects following dosages of up to 600 

 mg/kg in their diet for 20 to 45 days. 



Mercury: Contamination by mercury may re- 

 sult from natural soil sources, tailings from lead 

 mining, or from a variety of chemical wastes. Like 

 lead, mercury is a cumulative poison and its con- 

 tinued ingestion should be carefully controlled. 

 Wide variations in responses to various mercury 

 salts make generalizations dangerous. For exam- 

 ple, the LD50 value for mercuric chloride for rats 

 is 37 mg/kg, while that for mercurous chloride 

 was 210 mg/kg {5, 158). The use of mercury in 

 American agriculture has been restricted. 



Molybdenum salts can be significant water pol- 

 lution problems. Plant growth is not a sufficiently 

 sensitive criterion of molybdenum occurrence to 

 be used as an indicator of water safety for live- 

 stock since some plants can apparently accumulate 

 fairly large stores of molybdenum. Effects of mo- 

 lybdenum toxicity are aggravated by conditions 

 of copper deficiency in livestock. In Nevada, with 

 unusual local forage copper levels, molybdenosis 

 occurs only above forage levels of 5 to 6 mg/kg 

 for cattle and 10 to 12 mg/kg for sheep {46). 

 Although specific data on molybdenum toxicity 

 from drinking water sources are not readily avail- 

 able, some Florida waters where molybdenum 

 toxicity has occurred have contained up to 8.5 

 mg/1 molybdenum {38). 



Nitrates: Heavy application of nitrogenous ferti- 

 lizer can lead to leaching of nitrates in percolating 

 ground waters {128). Nitrates may also be sup- 

 plied as end products of aerobic stabilization of 

 organic nitrogen in sewage lagoons. There are 

 some indirect effects which complicate the nitrate 

 contamination picture. In ruminant animals, ni- 

 trates may be reduced in the rumen by the micro- 

 flora to nitrites which then exert toxic effects on 

 the animals. When present in waters in high con- 

 centrations, nitrates may also stimulate growth 

 of undesirable plants. 



Despite considerable interest in the potential 

 problems of nitrate toxicity, there are few specific 

 data. Campbell and others have reported met- 

 hemoglobinemia in catfle receiving water contain- 

 ing 2,790 mg/1 of nitrate. 



Selenium: Another case where plants cannot 

 serve as satisfactory indicators for animals is 

 presented by selenium, as previously indicated. 

 In some cases drainage water from irrigated areas 

 has been found to contain appreciable quantities 

 of selenium {143). Also, some selenium reaches 

 ground water by leaching from seleniferous plants. 



136 



