General Discussion 209 



of copper per acre a year, the net addition of copper to the soil 

 would be approximately ten pounds, or about 0.00025 per cent. 

 It would therefore require about forty years to accumulate 0.01 

 per cent of copper in the surface foot of soil. Inasmuch as, under 

 field conditions, this is not an injurious amount, there is little 

 likelihood, considering the district in a general way, that the 

 small residues of copper now coming down stream will accumu- 

 late to an injurious extent within a reasonable period of time. 

 Incidentally, it is of interest to note the large total losses of 

 copper (3094 lb. and 9720 lb. per day observed) formerly result- 

 ing from mining operations in the district. 



Possible Effects upon Health 

 With reference to the question of poisonous effects upon man 

 and animals of dissolved copper in irrigating and well-waters, 

 such effects, in general, are much less upon animals than upon 

 plant life. Moore and Kellerman state, for instance, that 0.02 

 gms. of copper may be absorbed daily by a man with safety." 

 This amount of copper would be contained in five gallons of 

 water containing one part per million of copper, the largest 

 amount of copper observed in a well-water in the district studied 

 being 0.53 p. p.m. It is of interest in this connection to note a 

 belief of the copper miners of the Rio Tinto in southern Spain, 

 where the wells are impregnated with copper, that one part of 

 copper per million of drinking water is permissible, but that two 

 parts per million result in "copper colic." "" In view of experi- 

 ments upon human subjects, however, it is more than likely that 

 deleterious effects observed are due to associated compounds in 

 the water. It is of importance to note that a strength of as 

 little as one part per million of copper in pure water will de- 

 stroy algae, which are common in clear water supplies freely 

 exposed to light and air. This fact may be made of use in clean- 

 ing ditches and reservoirs of aquatic growth, where the expense 

 is not too great. 



The germicidal effects of small amounts of copper in waters 

 of the district studied also have a bearing upon human health. 



11 U. S. D. A. Bur. PI. Ind., Bull. 64, p. 23. 



iia Conversation of J. W. Bennie, Clifton, Arizona. 



