Effect of Cyanuric Acid on the Inactivation of Cryptosporidium parvum under Hyperchlorination Conditions

Abstract

Cyanuric acid (CYA) is a chlorine stabilizer used in swimming pools to limit UV degradation of chlorine, thus reducing chlorine use and cost. However, CYA has been shown to decrease the efficacy of chlorine disinfection. In the event of a diarrheal incident, CDC recommends implementing 3-log10 inactivation conditions for Cryptosporidium (CT value = 15 300 mg·min/L) to remediate pools. Currently, CYA's impact on Cryptosporidium inactivation is not fully determined. We investigated the impact of multiple concentrations of CYA on C. parvum inactivation (at 20 and 40 mg/L free chlorine; average pH 7.6; 25 °C). At 20 mg/L free chlorine, average estimated 3-log10 CT values were 17 800 and 31 500 mg·min/L with 8 and 16 mg/L CYA, respectively, and the average estimated 1-log10 CT value was 76 500 mg·min/L with 48 mg/L CYA. At 40 mg/L free chlorine, 3-log10 CT values were lower than those at 20 mg/L, but still higher than those of free chlorine-only controls. In the presence of ∼100 mg/L CYA, average 0.8- and 1.4-log10 reductions were achieved by 72 h at 20 and 40 mg/L free chlorine, respectively. This study demonstrates CYA significantly delays chlorine inactivation of Cryptosporidium oocysts, emphasizing the need for additional pool remediation options following fecal incidents.

Outbreaks associated with treated recreational water — United States, 2000–2014

“…Chlorine is the primary barrier to the transmission of pathogens in treated recreational water. At CDC‐recommended concentrations of at least 1 ppm, free available chlorine inactivates most pathogens within minutes although extremely chlorine‐tolerant Cryptosporidium can survive for >7 days . Cryptosporidium is transmitted when a diarrheal incident (i.e., a high‐risk Cryptosporidium contamination event) occurs in the water and the contaminated water is ingested.…”

Ancient Evolution and Recent Evolution Converge for the Biodegradation of Cyanuric Acid and Related Triazines

“…An impediment to developing a solution for swimming pool water purification is the susceptibility of the CAH enzyme to inactivation due to oxidization by hypochlorite and hypochlorous acid, which are present in the chlorinated waters (90). Yeom et al showed that CAH activity declined as a function of increasing chlorine levels in the municipal pool waters that were treated (89).…”

Structure of the Cyanuric Acid Hydrolase TrzD Reveals Product Exit Channel

“…In waters requiring disinfection, chlorine dissipates over time but cyanuric acid is extremely stable, accumulates, and with increasing concentration, it sequesters all of the free chlorine and diminishes its effectiveness in destroying viruses, bacteria and protozoa5. In this context, a facile, enzymatic method for removing cyanuric acid from water has been sought.…”