phorus concentrations are associated with the 

 eutrophication of waters that is manifest in un- 

 pleasant algal or other aquatic plant growths when 

 other growth-promoting factors are favorable; that 

 aquatic plant problems develop in reservoirs or 

 other standing waters at phosphorus values lower 

 than those critical in flowing streams; that reser- 

 voirs and other standing waters will collect phos- 

 phates from influent streams and store a portion of 

 these within the consolidated sediments; that phos- 

 phorus concentrations critical to noxious plant 

 growths will vary with other water quality char- 

 acteristics, producing such growths in one geo- 

 graphical area but not in another. 



Because the ratio of total phosphorus to that 

 form of phosphorus readily available for plant 

 growth is constantly changing and will range from 

 two to 17 times or greater, it is desirable to estab- 

 lish limits on the total phosphorus rather than the 

 portion that may be available for immediate plant 

 use. Most relatively uncontaminated lake districts 

 are known to have surface waters that contain 10 

 to 30 /ig/1 total phosphorus as P; in some waters 

 that are not obviously polluted, higher values may 

 occur (4). Data collected by the Federal Water 

 Pollution Control Administration, Division of Pol- 

 lution Surveillance, indicate that total phosphorus 

 concentrations exceeded 50 /tg/1 (P) at 48 percent 

 of the stations sampled across the Nation (6). 

 Some potable surface water supplies now exceed 

 200 /xg/1 (P) without experiencing notable prob- 

 lems due to aquatic growths. Fifty micrograms per 

 liter of total phosphorus (as P) would probably 

 restrict noxious aquatic plant growths in flowing 

 waters and in some standing waters. Some lakes, 

 however, would experience algal nuisances at and 

 below this level. 



Critical phosphorus concentrations will vary 

 with other water quality characteristics. Turbidity 

 and other factors in many of the Nation's waters 

 negates the algal-producing effects of high phos- 

 phorus concentrations. When waters are detained 

 in a lake or reservoir, the resultant phosphorus 

 concentration is reduced to some extent over that 

 in influent streams by precipitation or uptake by 

 organisms and subsequent deposition in fecal pel- 

 lets or dead organism bodies. See the report of the 

 Subcommittee for Fish, Other Aquatic Life, and 

 Wildlife, and the section on Plant Nutrients and 

 Nuisance Organisms for a more complete dis- 

 cussion of phosphorus associations with the en- 

 richment problem. 



At concentrations of complex phosphates of 

 the order of 100 /xg/1, diflSculties with coagulation 

 are experienced. 



Paragraph 16: Total Dissolved Solids (Filterable 

 Residue) 



Drinking Water Standards (70) recommend 

 that total dissolved solids not exceed 500 mg/1 

 where other more suitable supplies are available. 

 It is noted, however, that some streams contain 

 total dissolved solids in excess of 500 mg/1. For 

 example, the Colorado River at the point of with- 

 drawal by the Metropolitan Water District of 

 Southern California has a total dissolved solids 

 concentration up to 700 mg/1. 



High total dissolved solids are objectionable 

 because of physiological effects, mineral taste, or 

 economic effect. High concentrations of mineral 

 salts, particularly sulfates and chlorides, are asso- 

 ciated with corrosion damage in water systems. 

 Regarding taste, on the basis of limited research 

 work underway in California, limits somewhat 

 higher than 500 mg/1 are probably acceptable to 

 consumers of domestic water supplies. It is likely 

 that levels set with relation to economic effects are 

 controlling for this parameter. 



Increases in total dissolved solids from those 

 normal to the natural stream are undesirable and 

 may be detrimental. 



It is recommended that the permissible value 

 for total dissolved solids be set at 500 mg/1 in 

 view of the above evaluation. Further, it is recom- 

 mended that research work be sponsored to obtain 

 more information on total dissolved solids in 

 water relating to physiological effects, consumer 

 attitudes toward taste, and economic considera- 

 tions. 



Paragraph 17: Uranyl Ion 



The standard for uranyl ion (UOj^) is estab- 

 lished on the basis of its chemical properties rather 

 than on the basis of its being a radioactive mate- 

 rial. It is being added to Drinking Water Stand- 

 ards (10). Uranyl ion is of concern in drinking 

 water because of possible damage to the kidneys. 

 The threshold level of taste and the appearance of 

 color due to uranyl ion occur at about 10 mg/1 

 which is much less than the safe limit of ingestion 

 of this ion insofar as adverse physiological effects 

 are concerned. 



The Public Health Service adopted the figure 

 of 5 mg/1 which is one-haff the limit based on taste 

 and color and, therefore, there is a considerable 

 factor of safety in the adoption of 5 mg/1. 



Paragraph 18: Carbon Chloroform Extract (CCE) 



A limit of 0.2 mg/1 carbon chloroform extract 

 in drinking water is recommended in the Drinking 

 Water Standards "as a safeguard against the intru- 

 sion of excessive amounts of potentially toxic ma- 



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