vestigations of stream basins {178, 180) have 

 demonstrated the value of these criteria in assessing 

 the quahty of raw water. Maintenance of quality 

 within these recommendations should insure suffi- 

 ciendy low concentrations of pathogenic micro- 

 organisms that no hazard to animals or man should 

 result from the use of the water on even those crops 

 which are consumed raw. 



In the study of the Red River of the North, 

 North Dakota-Minnesota (178), Salmonella were 

 not recovered from a reference point upstream 

 from the Fargo and Moorhead municipal treatment 

 plants and from a sugar company plant at Moor- 

 head. Total and fecal coliforms at this upstream 

 reference point were 500/100 ml and 100/100 

 ml, respectively. Salmonella were recovered in the 

 three sources of waste and in the river below the 

 discharges, the river samples showing 75,000 coli- 

 forms/ 100 ml and 15,500 fecal coli/100 ml. It is 

 suggested in that report that the stream should be 

 maintained at not more than 5,000 coliforms/100 

 ml even at critical periods of riverflow. Such a 

 standard could be maintained by secondary treat- 

 ment plus disinfection of the waste sources. 



In a similar, but more extensive, study of the 

 South Platte River Basin in Colorado {180), Sal- 

 monella recoveries have not yet been reported, but 

 maximum total coliforms of 5,000/100 ml and 

 maximum fecal coli of 1,000/100 ml were recom- 

 mended. In this study also, attention was given to 

 dissolved oxygen (DO) and 5-day, 20 C BOD 

 levels. Minimum levels of 4 mg/1 DO and a maxi- 

 mum of 20 mg/1, 5-day 20 C BOD levels were also 

 recommended for water used primarily for irriga- 

 tion. These criteria likewise are consistent with 

 quality that can be maintained by secondary treat- 

 ment plus disinfection of all waste sources. 



Toxicity to Animals or Humans Through 

 Accumulation in Plants 



Selenium is an example of an element which 

 may occur in soils in trace amounts, yet which may 

 be accumulated in certain cereals and pasture 

 plants without apparent injury, but in quantities 

 harmful to animals or humans when consumed. 

 Deficiencies of this element in animal diets may 

 result in white muscle disease, but an excess pro- 

 duces conditions known as "alkali disease" and 

 "blind staggers." Trelease and Beath (767) have 

 noted that selenium absorbed by grasses and ce- 

 reals enter the food chain of animals and humans. 

 Molybdenum is another example of an element 

 which can accumulate in plants and become detri- 

 mental to livestock. 



There is no evidence to date to indicate that 

 selenium or molybdenum occurrence in natural ir- 

 rigation water is a significant factor. It is important 

 to point out, however, that pollution of irrigation 

 waters by industrial sources could introduce harm- 

 ful concentrations of these and other elements. 



Suspended Solids: Suspended solids in irrigation 

 water can affect plant growth and quality in sev- 

 eral ways. Deposition of colloidal particles on the 

 soil surface can produce crusts which inhibit water 

 infiltration and seedling emergence. This same de- 

 position and crusting can reduce soil aeration to a 

 level where it impedes plant development. High 

 colloidal content in water used for sprinkler irriga- 

 tion could result in deposition of films on leaf sur- 

 faces which could reduce photosynthetic activity 

 and thereby deter growth. Where sprinkler irriga- 

 tion is used for leafy vegetable crops such as let- 

 tuce, sediment may accumulate on the growing 

 plant, affecting the marketability of these products. 



Radionuclides: There are no generally accepted 

 standards for control of radioactive contamination 

 in irrigation water. For most radionuclides, the 

 use of USPHS Drinking Water Standards (775) 

 appear to be reasonable for irrigation water. Sup- 

 plies containing not in excess of 3 and 10 pc/1, 

 respectively for radium-226 and strontium-90 

 would be acceptable without consideration of other 

 radioactive sources. In the known absence of 

 strontium-90 and alpha-emitting radionuclides, the 

 water supply is considered acceptable if the gross 

 beta activity does not exceed 1,000 pc/1. If the 

 gross beta activity is in excess of this amount, a 

 more complete radiochemical analysis is required 

 to determine that the sources of radiation exposure 

 are within the limits of the Radiation Protection 

 Guides. One state, Washington, has proposed such 

 a standard for irrigation water {188). 



The limiting factor for radioactive contamina- 

 tion in irrigation is its transfer to foods and even- 

 tual intake by humans. Such a level of contamina- 

 tion would be reached long before any damage to 

 plants themselves could be observed. Plants can 

 absorb radionuclides in irrigation water in two 

 ways: direct contamination of foliage through 

 sprinkler irrigation, and indirectly through soil con- 

 tamination. The latter presents many complex 

 problems since eventual concentration in the soil 

 will depend on the rate of water application, the 

 rate of radioactive decay, and other losses of the 

 radionuclide from the soil. Some studies relating to 

 these factors have been reported {96, 107, 108, 

 112,114,127). 



Calculations, using the drinking water standards 

 listed above, indicate that irrigation water having 



163 



