Cyanuric Acid (CYA)

Cyanuric acid or stabilized CHLORINE products shall not be used at the following for all new construction, SUBSTANTIAL ALTERATION, or DISINFECTION equipment replacements after the effective date of this CODE: 1) SPAS; and 2) THERAPY POOLS.

Cyanuric acid (CYA) is effective in protecting available CHLORINE from UV degradation. The chemical associates with CHLORINE to form chlorinated isocyanurates: trichlor (trichloroisocyanuric acid) and dichlor (sodium dichloroisocyanururic acid). It can also be added as a separate chemical in the form of isocyanuric acid, commonly referred to as cyanuric acid. Trichlor is commonly found as tablets or sticks. Dichlor is a granular material, as is the isocyanuric acid. Products containing or forming cyanuric acid (CYA) must be clearly labeled and directions provided to the user for proper use, limitations, toxicity, cautions, and effects. The most important factor in POOL DISINFECTION is the presence of sufficient levels of free CHLORINE. CYA helps maintain free CHLORINE levels in outdoor POOLS. CYA is not a disinfectant, so it is not registered by the EPA. Stabilized CHLORINES are registered with the EPA as disinfectants; however, EPA has not reviewed efficacy data on CHLORINE in the presence of increasing stabilizer to date. The EPA reviewed efficacy data on dichlor and trichlor when it approved registrations for drinking water DISINFECTION. However, these data are not directly applicable to swimming POOLS where repeated doses lead to higher CYA levels. Minimum Disinfection Minimum CHLORINE levels should be increased by a factor of at least two when using CYA. Robinton et al. found that “50 MG/L of cyanuric acid produced pronounced retardation of the bactericidal efficiencies of solutions of calcium hypochlorite, trichloroiso-cyanuric acid, and potassium dichloroisocyanurate such that a four- to eightfold increase in the amount of "free" available residual CHLORINE may be necessary to attain the same degree of inactivation of the same organisms in the same interval of time”³⁴⁹. Laboratory studies by Warren and Ridgway show that addition of 50 MG/L cyanuric acid to 0.5 - 1.0 MG/L available CHLORINE resulted in a significant increase in the CT of Staphylococcus aureus, in parallel with the increase in available CHLORINE stability in sunlight. However, higher concentrations of cyanuric acid resulted in little to modest further increases in CT over that for 50 MG/L cyanuric acid. For example, the data suggest that for 50, 100 and 200 MG/L of cyanuric acid, the level of CHLORINE required for 99% kill of Staphylococcus aureus in one minute would be 1.9, 2.15, and 2.5 MG/L, respectively³⁵⁰. The MAHC has adopted a SAFETY factor of 2 so that 2 PPM is the minimum concentration of using stabilized products. More data are needed to understand the impact of increasing cyanurate levels on pathogen inactivation to assess what this level should be so the MAHC has adopted less than or equal to 100 PPM, as has the World Health Organization³⁵¹. The level of cyanurate allowed in outdoor AQUATIC VENUES is double that for non-stabilized CHLORINE, which is a SAFETY factor for the decrease in oxidative capacity. The MAHC has decided that from a public health standpoint it cannot support a prohibition of the use of cyanurate in most INCREASED RISK AQUATIC VENUES. The SAFETY margin of two times the level of non-stabilized product would also apply for increased indoor settings in addition to the requirement for a SECONDARY DISINFECTION SYSTEM and therefore prohibition in an INCREASED RISK VENUE cannot, at this time, be supported with a public health argument. The exception to this is operation of SPAS and THERAPY POOLS, which have large issues with efficacy of agents against pathogens in biofilms and difficulties with maintaining needed pH levels (spas) and the use by INCREASED RISK groups of patients (THERAPY POOLS). SPAS and THERAPY POOLS will, therefore, not be allowed to use cyanuric acid or stabilized CHLORINE products. Users should be aware that if AQUATIC VENUES using cyanuric acid or stabilized CHLORINE products have a fecal incident, they will need to close for more prolonged periods for a diarrheal fecal incident and HYPERCHLORINATION, circulate water through a SECONDARY DISINFECTION SYSTEM, or replace the water in the AQUATIC VENUE per MAHC Section 6.5.3.2.1³⁵². Indoor Pools There appears to be no operational or public health reason for INDOOR AQUATIC VENUES to use CYA. It is a stabilizer for degradation from direct sunlight and so likely has limited benefits for indoor POOLS despite some operators claiming a benefit for indoor POOLS with large glassed areas. However, the level of cyanurate allowed in outdoor AQUATIC VENUES is double that for non-stabilized CHLORINE which is a SAFETY factor for the decrease in oxidative capacity. The MAHC has decided that it cannot support, from a public health standpoint, a prohibition of the use of cyanurate in indoor settings. The SAFETY margin would also apply for indoor settings and therefore prohibition in an indoor setting would require specific data on the direct impact in indoor settings since the MAHC allows it in outdoor settings. CDC still does not recommend cyanuric acid use for indoor POOLS or hot tubs. The recommendation was underscored in a 2000 MMWR after investigating a Pseudomonas dermatitis/folliculitis outbreak associated with indoor POOLS and hot tubs in Maine, noting that cyanuric acid was added to an indoor POOL which reduces the antimicrobial capacity of free CHLORINE³⁵³,³⁵⁴. Users should be aware that if AQUATIC VENUES using cyanuric acid or stabilized CHLORINE products have a fecal incident, they will need to close for more prolonged periods for a diarrheal fecal incident and HYPERCHLORINATION, circulate water through a SECONDARY DISINFECTION SYSTEM, or replace the water in the AQUATIC VENUE per MAHC Section 6.5.3.2.1³⁵⁵. Effects of Cyanuric Acid on Microbial Inactivation There are a large number of references on the effect of CYA on kill times (CT Values). In general, they show that the presence of CYA increases CT VALUES, and the amount of this increase depends on the pH and the ratio of CYA to available CHLORINE. However, there are few reports that relate specifically to the issue of what levels of available CHLORINE and cyanuric acid are required to maintain a swimming POOL in a biologically satisfactory state. Studies examining the effect of cyanuric acid on the DISINFECTION capacity of CHLORINE show that using cyanuric acid or stabilized CHLORINE slows down the inactivation times on bacteria, algae, protozoa (Naegleria gruberi and Cryptosporidium parvum), and viruses. Yamashita et al. concluded the addition of cyanuric acid increased the time needed for DISINFECTION of 12 virus types by a factor of 4.8-28.8 compared to free CHLORINE alone³⁵⁶,³⁵⁷. Table 5.7.3.1.3.1: 99.9% Inactivation time in buffer studies, 0.5 PPM (MG/L) FAC, 25 C Organism No CYA, min 30 PPM (mg/L) CYA, min Poliovirus 1 0.8 5.6 Coxsackievirus A24 0.5 14.4 Enterovirus 70 0.12 2.5 Adenovirus type 3 0.14 2.1 Table 5.7.3.1.3.2: 99.9% Inactivation time in POOL water studies, 1.0 PPM (MG/L) FAC, 25 C Organism No CYA, min 30 PPM (mg/L) CYA, min Poliovirus 1 0.4 4.4 In a later study, Yamashita et al. ³⁵⁸ found “Total plate counts ranged from 0 to 1 per mL in the swimming POOLS treated with sodium hypochlorite and 0 to 51 in those with trichloroisocyanurates. In 11 of 12 water samples of 3 swimming POOLS using trichloroisocyanurates, poliovirus type 1 survived after 2 minute contact while in 5 samples poliovirus type 1 survived after 5 minute contact.” The researchers concluded this showed that the risk of viral infection is greater in swimming POOL water treated with chlorinated isocyanurates than that with sodium hypochlorite. The addition of CYA similarly impaired the inactivation of poliovirus³⁵⁹. Cyanuric acid, used as CHLORINE stabilizer in swimming POOL waters, had a relatively minor effect on the algicidal efficiency of FREE CHLORINE³⁶⁰. There are few data regarding protozoa and the effect of CYA on inactivation though the DISINFECTION rate for Naegleria gruberi was reduced by cyanuric acid in laboratory-controlled CHLORINE demand free conditions³⁶¹. Shields et al.³⁶² extended the previous findings by demonstrating that cyanuric acid significantly decreases the rate of inactivation for Cryptosporidium parvum OOCYSTS. In this study a three-log reduction of OOCYSTS was found to take place in the presence of 20 PPM (mg/L) FAC. When 50 PPM (mg/L) CYA was introduced, the 10-hour kill rate was less than ½ log. Pseudomonas inactivation in the presence of CYA was also studied in POOL water and it was found that increased CYA concentrations lengthened the kill times. The effect of cyanuric acid was greater as the concentration of CHLORINE in the water decreased³⁶³. Favero et al. found that at free CHLORINE concentrations of more than 0.5 PPM (mg/L), P. aeruginosa was rarely found except in those POOLS which used sodium dichloroisocyanurate as a POOL disinfectant. Three private swimming POOLS using sodium dichloroisocyanurate as a POOL disinfectant were found to contain large numbers of the potential pathogen, P. aeruginosa³⁶⁴. Fitzgerald found concentrations of 25, 50, and 100 mg of cyanuric acid per liter had large effects on the Pseudomonas kill rate of 0.1 MG/L free CHLORINE but this effect diminished with increasing free CHLORINE content (0.25, 0.5 mg/L). Fitzgerald found concentrations of 25, 50, and 100 mg of cyanuric acid per liter had little effect on the kill rate of 0.5 mg of CHLORINE plus 0.1 mg of NH4-N per liter; however, cyanuric acid did reduce the time required for 99.9% kills when tested in the presence of higher concentrations of ammonia³⁶⁵. The basis for this finding should be explored further. Fecal Accident Response The use of stabilized CHLORINE is not recommended for HYPERCHLORINATION in RWI outbreaks, or in response to fecal accidents. Present MAHC requirements for HYPERCHLORINATION and POOL remediation are ineffective for POOLS using cyanurate-stabilized CHLORINE. Estimated Cryptosporidium inactivation times are much longer, which will require substantially longer closure times³⁶⁶. Toxicity The maximum CYA concentration of 100 PPM (mg/L) should be considered protective from a toxicological perspective. Using an assumption that 100 mL of POOL water is swallowed per swim session; the World Health Organization (WHO) concluded that CYA levels in POOLS should be below 117 PPM (mg/L). This is based on a tolerable daily intake (TDI) for anhydrous sodium dichloroisocyanurate (NaDCC) of 2 mg/kg of body weight, which translates into an intake of 20 mg of NaDCC (or 11.7 mg of CYA per day) for a 10 kg child. The U.S. EPA SWIMODEL, relying on somewhat lower exposure assumptions, would yield a higher acceptable level for CYA. Research Though the data shows CYA use increases the inactivation time of many pathogens, the MAHC would like to have a study done on specific pathogens and inactivation rates at differing CYA levels, up to at least 200 PPM (mg/L). Further research on the inhibitory effect of cyanuric acid on DISINFECTION should evaluate the level at which cyanuric acid can still protect CHLORINE from UV and also balance the inactivation rate of the most common AQUATIC VENUE pathogens. The effect of pH in the presence of cyanuric acid should also be investigated. Additionally, a test kit should be created to test lower and higher levels of CYA. The current products on the market are not very accurate and need to operate over a wider range of CYA levels. During RWI outbreaks, it is strongly recommended that the investigation team measure CYA levels.