more units of pH higher or lower than pH-7.4, a 

 pain response may be elicited. 



In addition to the factors concerning hydrogen- 

 ion concentration and buffer capacity, the tonicity 

 of the fluid in contact with the eye is an important 

 consideration to minimize irritation or pain re- 

 sponse. Lacrimal fluid is isotonic (i.e., having the 

 same osmotic pressure) with blood and has a to- 

 nicity equivalent to that of a 0.9-percent sodium 

 chloride solution. Early studies by Hind and 

 Goyan ( 7 ) showed that a sodium chloride equiva- 

 lent range of 0.5 percent to 2.0 percent concentra- 

 tion was well tolerated. Later, Riegelmann, 

 Vaughan and Okumoto (5 ) , and Riegelmann and 

 Vaughan (4) suggested that the range be nar- 

 rowed to the equivalence of between 0.7 percent 

 to 1.5 percent sodium chloride. 



Tonicity of water used for recreation will be 

 important in reducing or preventing eye irritation 

 only in those cases where there is prolonged ex- 

 posure of the eye to water. The usual type of 

 recreational bathing and swimming which most 

 people engage in does not usually involve pro- 

 longed exposure of the eye to water. Hence, tonic- 

 ity of recreation waters is of much less importance 

 than the hydrogen-ion concentration and the buffer 

 capacity in preventing or reducing eye irritation to 

 bathers and swimmers. 



An ideal water that would be non-irritating to 

 the majority of bathers would be one that is rela- 

 tively unbuffered and has a sodium chloride 

 equivalent of 0.9 percent and a pH of 7.4. Since 

 the ideal can seldom, if ever, be achieved, alter- 

 nate values are necessary. While the lacrimal fluid 

 can adjust the pH of an unbuffered solution from 

 as low as 3.5 or as high as 10.5 to within tolerable 

 limits withm a short time, these limits of pH have 

 no practical value as unbuffered water is not 

 found in nature under usual conditions. Almost 

 all natural waters have some buffer capacity. 

 Therefore, to minimize eye irritation to bathers, it 

 seems desirable to suggest that for natural waters 

 with low buffer capacity, the pH range be between 

 5.0 and 9.0. Since most natural waters have more 

 than a low buffer capacity, a more desirable range 

 of pH would be 6.5 to 8.3. 



In summary, when water quality standards are 

 proposed for swimming, bathing, and other similar 

 uses, consideration should be given to those 

 physico-chemical properties that may cause or 

 contribute to eye irritation. Of principal impor- 

 tance is the hydrogen-ion concentration with code- 

 pendence upon the buffer capacity of the water. 

 Ideally, the pH of water should be approximately 

 the same as the pH of lacrimal fluid which is about 

 7.4 for most people. Since the lacrimal fluid has a 

 high buffering capacity, a range of pH values from 



6.5 to 8.3 can be tolerated under average condi- 

 tions. If the recreation water is relatively free of 

 dissolved solids and has a very low buffer capacity, 

 pH values from 5.0 to 9.0 should be acceptable. 

 However, for recreation water having a pH less 

 than 6.5 or greater than 8.3, waste discharge 

 standards should include prohibition against re- 

 leases that will increase the buffer capacity of the 

 receiving waters and yet maintain the pH below 

 6.5 or greater than 8.3. Tonicity standards do not 

 seem to have any practical value. 



references 



(/) Hind, H. W., and F. M. Goyan. 1947. A new 

 concept of the role of hydrogen-ion concentration 

 and buffer systems in the preparation of ophthalmic 

 solutions. J. Am. Pharm. Assoc. (Sci. Ed.), 36: 33- 

 41. 



(2) Hind, H. W., and F. M. Goyan. 1949. The hydro- 

 gen-ion concentration and osmotic properties of 

 lacrimal fluid. J. Am. Pharm. Assoc. (Sci. Ed.), 

 38: 477-479. 



(i) Johnson, R. D. Role of tonicity, pH, and buffers as 

 they apply to pharmaceutical development of 

 ophthalmic preparations (unpublished article). 



(4) Riegelmann, S., and D. G. Vaughan, Jr. 1958. 

 A rational basis for the preparation of ophthalmic 

 solutions. Part 1. J. Am. Pharm. Assoc. (Prac. 

 Pharm. Ed.), 19: 474-477. 



(5) Riegelmann, S., D. G. Vaughan, Jr., and M. 

 Okumoto. 1955. Compounding ophthalmic solu- 

 tions. J. Am. Pharm. Assoc. (Prac. Pharm. Ed.), 

 16: 742-746. 



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