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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

Cyanuric chloride (2,4,6-trichloro-1,3,5-triazine) has a low solubility and is hydrolytically unstable therefore a test on toxicity to aquatic algae and cyanobacteria is technically not feasible. Therefore the results for the degradation product of cyanuric chloride (isocyanuric acid) are suitable as well. Isocyanuric acid was tested for toxicity to algae in a 72 h-static test according to OECD guideline 201. The EC50 based on the area under the growth curve and based on the growth rate was determined to be 620.0 mg/L and 780.0 mg/L, 800.0 mg/L, respectively. The No-observable effect concentration (NOEC) was determined to be 62.5 mg/L (area method) and 250 mg/mL and 125.0 mg/L (growth velocity method), respectively.

Key value for chemical safety assessment

EC50 for freshwater algae:
800 mg/L
EC10 or NOEC for freshwater algae:
125 mg/L

Additional information

Cyanuric chloride (2,4,6-trichloro-1,3,5-triazine) has a low water solubility and is hydrolytically unstable. Therefore a test with this substance is technically not feasible. Two hydrolysis products are to be expected which are 2-chloro-4,6-dihydroxy- 1,3,5-s-triazine and cyanuric acid (2,4,6 -trihydroxy-1,3,5 -triazine). Cyanuric acid is in water in equilibrium with isocyanuric acid.

Key study:

In the study 97-0700-FGO_en the analogous substance Isocyanuric acid, that is a hydrolysis product of the hydrolysis of cyanuric chloride, was tested for toxicity to algae in a 72 h-static test according to OECD guideline 201. The EC50 based on the area under the growth curve and based on the growth rate was determined to be 620.0 mg/L and 780.0 mg/L, 800.0 mg/L, respectively.

Supporting study:

In the SIDS report (SIDS-report-108-77-0_2001) it was shown that the toxicity of 2-chloro-4,6-dihydroxy- 1,3,5-s-triazine can be reliably approximated with QSAR methods. Therefore the calculated value of EC50(algae) of 909 mg/L for this substance is deemed reliable.

For cyanuric acid no measured value for algal toxicity is available from the SIDS report, but a IC50(algae) of 800 mg/L is reported for isocyanuric acid. So this latter value can be regarded as a worst case for toxicity of 2,4,6-trichloror-1,3,5-triazine to aquatic algae and cyanobacteria.