The World Health Organization (WHO) has recommended that a maximum concentration of 70 µg/L (as cyanide) be used as a guideline for total cyanogen compounds in drinking water. Cyanogen chloride can react with chlorine to form nitrogen trichloride (trichloramine). Cyanogen chloride can be formed from the oxidation of L-histidine and of glycine. In Blatchley's work, he detected no cyanogen chloride in swimming pool samples in his first paper which he attributed to the relatively short half-life in the presence of chlorine -- about one hour in the presence of 0.5 ppm mg/L FC at 25ºC, pH 7. In his second paper, he measured levels mostly in the 1 to 30 µg/L range which is below WHO (70 µg/L), EPA (200 µg/L), ACGIH (300 µg/L) limits.
It seems to me that cyanogen chloride isn't the worst of the disinfection by-products in terms of typical concentrations found in real pools. It looks more like nitrogen trichloride in high active chlorine level pools is more common and high TTHMs especially in pools with more bromide in the water (since the brominated THMs are more carcinogenic) are more common. High chloroform levels are also found but it's less clear about the health issues on its own and instead is more of a marker for the more serious brominated THMs. The nitrosamines might also be an issue, but that is discussed in Nitrosamine Carcinogens Also Swim in Chlorinated Pools other papers that show that hot tubs had 313 ng/L medium concentrations that are 500-fold higher than drinking water limits at 0.7 ng/L for a 1 in a million cancer risk (though obviously one is not drinking spa water so the issue is how much gets absorbed through the skin and how much gets inhaled from aerosols).
Hi Richard, I attach a report from a research institute in Denmark that recorded cyanogen chloride concentrations as high as 140 ug/l after medium pressure UVc irradiation. The upper 15min exposure level in air under European regulations is 0.77mg/m3. If the water was degassed by a class of children jumping into the water, then it may be possible the upper atmospheric limit could be exceeded.
Cyanogen chloride is lipid soluble, volatile and very toxic, it is also unstable so analysis needs to be conducted immediately after sample collection. We are looking at this reaction product along with THM formation in water exposed to sunlight and UV irradiation. It is still early days but we are also detecting high transient concentrations.
The UV in sunlight is quite different in its spectrum to that of medium-pressure UV so it will be interesting to see if 1) cynogen chloride is indeed mostly produced from the medium-pressure UV system itself and 2) if it is also produced by sunlight exposure.