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Toxicity to terrestrial plants

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Description of key information

The chlorinated isocyanurates are unstable in the environment, because the free available chlorine is rapidly reduced.  CYA, or its salt, is the stable degradation product. Therefore, CYA, or its sodium salt, is the substance of interest for terrestrial plant studies.

Key value for chemical safety assessment

Additional information

Plants are already exposed to CYA from natural sources in soil. A study conducted in 1917 showed that CYA naturally occurs in soils at concentrations of 0.9 to 6.5 ppm (1). The presence and identification of the levels of CYA found in the study predate the large scale commercial manufacture and use of products which breakdown to CYA thus providing evidence that the substance occurs due to other sources.

CYA is also present in soil as a result of plant protection products such as the S-triazines, atrazine and simazine which have been commercially used for over 40 years (2). The s-triazine herbicides undergo enzyme catalysed degradation yielding CYA as an intermediate, which is then hydrolytically processed to ammonia and carbon dioxide. Urea and other urea based compounds used as fertilizers can also form CYA as an intermediate.

CYA in soil is rapidly degraded by microorganisms. Anaerobic studies performed on a variety of soil types showed that CYA is readily degraded to carbon dioxide by microorganisms, which multiply in anaerobic conditions and do not require acclimatisation to be active for CYA decomposition (3) The mineralization of CYA in soil has also been found to occur from investigation of the nitrification of triazine nitrogen.(4) Certain plant species are capable of metabolizing CYA. A study with corn showed that it is capable of metabolizing 80% of CYA (5).

The algae toxicity showed CYA has no toxic effects to algae with a 48 h EC50 >1000 mg/kg 6

Due to the natural occurrence of CYA in soils and the evidence of the rapid degradation by microorganisms an acute toxicity study on plants would yield no pertinent information and is therefore scientifically unjustified.


1 Wise L E and Walters E H (1917) Isolation of Cyanuric Acid from Soil. Journal of Agricultural Research. 10(2) 85 - 91.

2. Müllar PW and Payot PH (1966) Fate of 14C-labelled Triazine herbicides in plants, Isotopes and Weed Research Proceedings of the IACA Symposium, Vienna, Austria, 1966 p61-70

Cook AM and Hutter R (1981) sTriazines as Nitrogen Sources for Bacteria J. Agr. Food. Chem 29:(6) 1135 -1143

Eaton RW and Karns JS (1991) Cloning and Analysis of s-Triazine catabolic genes from Pseudomonas spp. strain NRRLB-12227, Journal of Bacteriology p.1215-1222, Vol. 173, No. 3

3. Saldick (1974) Biodegradation of Cyanuric Acid, Applied Microbiology, 28 (6) 1004 – 1008

4,5. Müllar PW and Payot PH (1966) Fate of 14C-labelled Triazine herbicides in plants. Isotopes and Weed Research Proceedings of the IACA Symposium, Vienna, Austria, 1966 p61-70

6. Vryenhoef H, Hill, J W F (2007) Monosodium salt of cyanuric acid: Navicula pelliculosa; Algal inhibition test. SafePharm Laboratories Ltd., Project No. 2255/0001.

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