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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

Data is provided for both TCCA and CYA. A modified method based on the ASTM method E645-85 for the TCCA study. The study is in principle an efficacy study but demonstrates the inhibitory effect of trichloroisocyanuric acid against algae. Two algal growth inhibition studies have been performed for the monosodium salt of cyanuric acid  freshwater algae (OECD 201) and one study with marine algae.

Key value for chemical safety assessment

EC50 for freshwater algae:
0.5 mg/L

Additional information


An efficacy study is available (Prince 1990) which principally demonstrated the inhibitory effect of TCCA against three freshwater algal species. In the study 0.5 mg/L TCCA killed ≥ 90% of the algal species Euglena gracilis, Chlorella pyrenoidosa and Scenedesmus obliguus following a three hour contact time demonstrating that TCCA is very toxic to algae.


Freshwater algae Navicula pelliculosa were exposed to 313, 625, 1250, 2500 and 5000 mg/L (equivalent to 237, 473, 945, 1890 and 3780 mg/L cyanuric acid). The test concentration of 5000 mg/L was the highest attainable test concentration that could be prepared due to the solubility of the test material. After 96 h exposure EC50 values of > 5000 mg/L (equivalent to 3780 mg/L cyanuric acid) were obtained. The NOEC was 1250 mg/L (equivalent to 945 mg/L cyanuric acid)

In another study with freshwater algae Selenastrum capricornutum were exposed to 56, 100, 320, 560 and 1000 mg/L nominal concentrations of cyanuric acid. Exposure to cyanuric acid did not appear to adveresely affect Selenastrum capricornutum until 72 hours of exposure. The estimated 24 hour and 48 hour EC50s based on decrease of in vivo chlorophyll alpha were >1000 ppm while the calculated 72- and 96-hour EC50s were 872 and 712 ppm respectively. Based on decrease of cell numbers the 96 hour calculated EC50 was 655 ppm with 95% confidence limits of 439-977 ppm.

In a limit test marine algae Skeletonema costatum were exposed to a nominal concentration of 100 mg/L to the monosodium salt of cyanuric acid. The EC50 value was >100 mg/L (equivalent to 76 mg/L cyanuric acid) and correspondingly the NOEC was 100 mg/L (equivalent to 76 mg/L cyanuric acid). Analysis of the test preparations at 0 and 72 hours showed measured test concentrations to be near nominal and so the results are based on nominal test concentrations only.