enteritis, typhoid and paratyphoid fevers, leptospi- 

 rosis, cholera, vibriosis, and infectious hepatitis. 

 Other infections less commonly seen, at least in 

 the United States, are tuberculosis, brucellosis, lis- 

 teriosis, coccidiosis, swine erysipelas, ascariasis, 

 cysticercosis and tapeworm disease, fascioliasis, 

 and schistosomiasis. Isolation of the pathogens 

 themselves is far too slow and costly to consider 

 other than for research purposes and correlation. 



Of the types of irrigation commonly practiced, 

 sprinkling undoubtedly requires the best quality of 

 water from a microbiological point of view, as the 

 water and organisms are frequently applied directly 

 to that portion of the plant above the ground, and 

 especially for fruits and leafy crops such as straw- 

 berries, lettuce, cabbage, alfalfa, clover, etc., 

 which may be consumed raw. Flooding the field 

 may pose the same microbiological problems if the 

 crop is eaten without thorough cooking. Subirriga- 

 tion and furrow irrigation present fewer problems 

 as the water rarely reaches the upper portions of 

 the plant; and root crops, as well as normal leafy 

 crops and fruits, ordinarily do not permit penetra- 

 tion of the animal and human pathogens to the in- 

 side of the plant. Criteria for these latter types may 

 also depend upon the characteristics of the soil, 

 climate, and other variables which affect the sur- 

 vival of the microorganisms. 



Benefits can be obtained by coordinated opera- 

 tion of reservoir releases with downstream inflows 

 to provide sedimentation and dilution factors to 

 reduce markedly the concentrations of pathogens 

 in the water applied in irrigation (31, 84). 



Tanner (755) and Rudolfs, Falk, and Ragotzkie 

 {146) have reviewed the literature on the occur- 

 rence and survival of pathogenic and nonpatho- 

 genic enteric bacteria in soil, water, sewage, and 

 sludges, and on vegetation irrigated or fertilized 

 with these materials. It would appear from these 

 reviews that fruits and vegetables growing in in- 

 fected soil can become contaminated with patho- 

 genic bacteria and that these bacteria may survive 

 for periods of a few days to several weeks or more 

 in the soil and on vegetation. 



Falk (55) and Rudolfs, Falk, and Ragotzkie 

 {144) studied the relative incidence of coliform 

 organisms on tomatoes grown on three plots of 

 ground : one plot irrigated with settled sewage con- 

 currently with growth, one irrigated previous to 

 planting but not further, and one with no previous 

 or concurrent irrigation. Except for the tomatoes 

 wth abnormal stem ends, there was no material 

 difference in coliform counts per gram of tomatoes 

 from the three plots. These same authors further 

 found that Salmonella cerro and Shigella alkales- 

 cens organisms sprayed on growing tomatoes dis- 



appeared within 2 to 7 days, whereas organisms of 

 the coliform group remained for considerably 

 longer periods. 



Norman and Kabler {121) made coliform and 

 other bacterial counts in samples of sewage-con- 

 taminated river and ditch waters and of soil and 

 vegetable samples in the fields to which these 

 waters were applied. They found that although the 

 bacterial contents of both river and ditch waters 

 were very high, both soil and vegetable washings 

 had much lower counts. For example, where irri- 

 gation water had coliform counts of 230,000/100 

 ml, leafy vegetables had counts of 39,000/100 

 grams and smooth vegetables, such as tomatoes 

 and peppers, only 1,000/100 grams. High entero- 

 coccus counts accompanied high coliform counts 

 in water samples, but enterococcus counts did not 

 appear to be correlated in any way with coliform 

 counts in soil and vegetable washings. 



Dunlop and Wang {43) have also endeavored 

 to study the problem under actual field conditions 

 in Colorado. Salmonella, Ascaris ova and Enta- 

 moeba coli cysts were recovered from more than 

 50 percent of irrigation water samples contami- 

 nated with either raw sewage or primary-treated, 

 chlorinated effluents. Only one of 97 samples of 

 vegetables irrigated with this water yielded 5a/- 

 monella, but Ascaris ova were recovered from two 

 of 34 of the vegetable samples. Although cysts of 

 the human pathogen. Entamoeba histolytica, were 

 not recovered in this work, probably due to a low 

 carrier rate in Colorado, their similar resistance to 

 the environment would suggest that these orga- 

 nisms would also survive in irrigation water for a 

 considerable period of time. It should be pointed 

 out, however, that this work was done entirely 

 with furrow irrigation on a sandy soil in a semiarid 

 region, and the low recoveries from vegetables 

 cannot necessarily be applied to other regions or 

 to sprinkler irrigation of similar crops. In fact, 

 MUller {116) has reported that two places near 

 Hamburg, Germany, where sprinkler irrigation 

 was used, Salmonella organisms were isolated 40 

 days after sprinkling on soil and on potatoes, 10 

 days on carrots, and 5 days on cabbage and 

 gooseberries. 



MUller {117) has also reported that 69 of 204 

 grass samples receiving raw sewage by sprinkling 

 were positive for organisms of the typhoid-paraty- 

 phoid group {Salmonella). The bacteria began to 

 die off 3 weeks after sewage application; but 6 

 weeks after application, 5 percent of the samples 

 were still infected. These findings emphasize the 

 importance of having good quality water for 

 sprinkler irrigation. 



161 



