An evaluation of the inhibitory influence of cyanuric acid upon swimming pool disinfection.

ADEQUATE protection of swimming pool waters has been of paramount importance for many years to health officials who are charged with responsibility for the safety and health of the public. The use of the chlorine compounds or of chlorine gas has been written into practically every regulation concerned with the disinfection of drinking water. The limitations of chlorine for swimming pool water treatment have been discussed thoroughly over the years-its instability, its capacity for forming amines and other substances which are either less effective disinfecting agents or are irritating to the eyes of bathersare well known. New compounds which would eliminate these problems have been sought. One group of chemicals which has been proposed for use as swimming pool disinfectants is the chlorinated cyanurates, which made their appearance as sanitizing compounds and household bleaches in 1958. They appeared to be well adapted for swimming pool water disinfectants as they were soluble, neutral in pH, and provided a relatively stable chlorine residual in the presence of sunlight. A number of these products were placed upon the market and include: (1) trichloroisocyanuric acid, (2) dichloroisocyanuric acid, (3) potassium dichloroisocyanuric acid, (4) sodium dichloroisocyanurate. The literature concerned with these various compounds has been reviewed comprehensively by Anderson1 who undertook an evaluation of the effect of cyanuric acid on the bactericidal properties of chlorine under laboratory conditions at 200 C, approximately the conditions developed by Butterfield, et al.2 In this study, Anderson found that at a pH of 7.0 with Staphylococcus aureus as a test organism and a concentration of 0.25 mg/l of free residual chlorine, the time required to effect a 99 per cent kill was 0.5 minutes; 11 minutes when 25 mg/l of cyanuric acid was added to the chlorine solution; 15 minutes when 50 mg/l of cyanuric acid was used;