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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The analogous substance (2-chlor-4, 6-dihydroxy-1,3,5-triazin, mono sodium salt) was tested for ready biodegradability according to EU-method 4C-B and OECD guideline 301 E. The test item was considered to be not ready biodegradable. 

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

In the study Wotzka etal_1993_1994 on the biodegradation of cyanuric chloride a BOD = 0 was found. This study was considered to be not reliable and therefore this study was disregarded.

Due to the fast hydrolysis of the cyanuric chloride studies on the biodegradation using its degradation products are suitable as well. Therefore a read across approach with the a supporting, analogous substances was applied.

In the key study (90-0014-DGO) according to OECD guideline 301 E and EU-method C.4-B the biodegradation behaviour of the supporting substance (2-chlor-4, 6-dihydroxy-1,3,5-triazin, mono sodium salt) was assessed. The test revealed that after an exposure period of 28 days no biodegradation occurred. Therefore, the test item was considered to be not ready biodegradable. Additionally the biological oxygen demand of the test item was investigated in a supporting study (90 -0013 -DGO). After an exposure period of 5 days the test revealed that the BOD was 5 % at a concentration of 2 mg/L test item and 0 % at a concentration of 10 mg/L.

Further supporting studies with read-across substances (i.e. intermediate and final degradation products of the hydrolysis of cyanuric chloride) were performed:

- In the study 90-0013-DGO the biological oxygen demand of the read across substance (2-chlor-4, 6-dihydroxy-1,3,5-triazin, mono sodium salt (= intermediate degradation product of the hydrolysis of cyanuric chloride)) was measured in accordance to EU-method C. 5. The BOD was 5% and 0% at low and high concentrations, respectively.

- The test (study 89-0012-DKO) revealed that the read across substances (cyanuric acid (= final degradation product of the hydrolysis of cyanuric chloride)) is not inherently biodegradable.

The OECD SIDS report on cyanuric chloride on the aquatic toxicity of cyanuric acid and isocyanuric acid states as follows:

"The compound (cyanuric chloride) hydrolyses quickly to cyanuric acid in water via formation of 2,4-dichloro-6 - hydroxy-s-triazine and 2-chloro-4,6-hydroxy-s-triazine.

The tests found on biodegradation of 2-chloro-4,6-hydroxy-s-triazine and cyanuric acid are considered to be less reliable. In view of the limited toxicity to aquatic organisms of both substances and the low bioaccumulating potential of cyanuric acid, it is not necessary to perform a biodegradation study.

From the EQC model and the EUSES model (version 2.0) it can be deduced that 97-98% of cyanuric chloride will end up in the surface water. Therefore it is considered not necessary to conduct an adsorption-desorption study in soil. Some micro-organisms are able to degrade cyanuric chloride. It is not clear whether or not “normal” soil micro-organisms are able to degrade cyanuric chloride.

However in view of the low exposure that is expected for soil-micro-organisms, it is not necessary to conduct further testing."

Furthermore this OECD SIDS report on cyanuric chloride on the aquatic toxicity of cyanuric acid and isocyanuric acid argues:

"In fact several bacteria and fungi can use cyanuric acid as nitrogen source (references: Stephenson H. Jensen H.L., Abdel-Ghaffar A.S. (1969) Cyanuric acid as nitrogen source for micro-organisms Arch. Mikrobiol 67:1-5.; Hauck R., 1964 Nitrification of triazine nitrogen Agr. Food Chem. 12(2): 147 -151; Zeyer J., Huetter R. & Mayer P. (1980) Decomposition of cyanuric acid by microbes. Chemical abstracts, 60 Sewage, Wastes 92:313-314; Zeyer J., Bodmer J., Hütter R. (1981) Rapid degradation of cyanuric acid by Sporothrix schenckii. Zbl. Bakt. Hyg., I. Abt. Orig. C 2: 99-110; Myskow W., Lasota T., Stachyra A. (1983) Cyanuric acid- a s-triazine derivative as a nitrogen source for some soil microorganisms. Acta Microbiol Pol 32(2): 177-183; Beilstein P., Hütter R. 1980 Enzymatic cleavage of cyanuric acid by a hydrolase Experimentia 36: 1457; Cook A., Hütter R. (1981) s-Triazines as nitrogen sources for bacteria J. Agr. Food Chem. 29: 1135-1143; Cook A., Beilstein P., Grossenbacher H. & Hütter R. (1985) Ring cleavage and degradative pathway of cyanuric acid in bacteria Biochem. J. 231:25-30; Jutzi K., Cook A., Hütter R. (1982) The degradative pathway of the s-triazine melamine Biochem. J. 208: 679-684; Jessee J., Benoit R., Hendricks A. (1983) Anaerobic degradation of cyanuric acid, cysteine, and atrazine by a facultative anaerobic bacterium. Appl Environm Microbiol. 45(1): 97-102; Degussa AG (1989) Zahn-Wellens-Test zum biologischen Abbau von Cyanursäure Degussa, 89-0012 DKO)"