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Ecotoxicological information

Short-term toxicity to aquatic invertebrates

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Description of key information

Static toxicity studies have been  performed on Daphnia magna with TCCA, NaDCC and CYA.

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
0.17 mg/L

Additional information

Studies are available for sodium dichloroisocyanurate and trichloroisocyanuric acid

The chlorinated isocyanurates (trichloroisocyanuric acid and sodium dichloroisocyanurate) produce free available chlorine, in the form of hypochlorous acid (HOCl) as they dissolve in water. As the equilibria involve all of the possible chlorinated isocyanurates, the toxicity of trichloroisocyanuric acid (TCCA), sodium dichloroisocyanurate (NaDCC) and sodium dichloroisocyanurate dihydrate (NaDCC.2H2O) will be virtually equivalent at the same available chlorine concentration. The parent compound for all chlorinated isocyanurates is isocyanuric acid (cyanuric acid). All of the chlorinated isocyanurates are essentially equivalent, once they are dissolved in water at the low concentrations at which they are used.

Based upon the available chlorine content and the dissociation constants for the chlorinated isocyanurate species, TCCA is considered to be the most toxic, or reactive form. Therefore test results for this species will be considered as the "worst-case" for the chlorinated isocyanurates allowing read-across for the less reactive dichlorinated forms.

Additionally studies are available for the degradation substance CYA.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 chronic ecotoxicity studies.

NaDCC: In a 48 h static acute toxicity test (LeBlanc 1978) Daphnia magna were exposed to nominal test concentrations of 0.15, 0.17, 0.19, 0.22, 0.24, 0.28, 0.32 mg/L NaDCC dihydrate for 48 h. The 48 h LC50 was determined to be 0.196 mg/L. In an acute toxicity study with marine aquatic invertebrates (Anderson 2002) mysid shrimp were exposed to nominal concentrations of 0.625, 1.25, 2.5, 5 and 10 mg/L sodium dichloroisocyanurate for 96 hours. The 96 h LC50 was determined to be 1.65 mg/L. TCCA: Two acute daphnia studies have been performed with TCCA. In the first study (LeBlanc 1976) Daphnia magna were exposed to 0.10, 0.16, 0.24, 0.37 and 0.56 mg/L nominal concentrations of TCCA. The 48 h LC50 of trichloroisocyanuric acid was 0.21 mg/L. In a second study (Barrows 1985) Daphnia magna were exposed to 0.13, 0.22, 0.36, 0.6 and 1 mg/L nominal concentrations of trichloroisocyanuric acid. The 48 h LC50 was determined to be 0.17 mg/L. CYA: In a 48 h static acute toxicity test (LeBlanc 1978) Daphnia magna were exposed to nominal concentrations of 1,000, 600, 360, 220, 130 and 100 mg/L cyanuric acid. No mortalities occurred at the highest concentration test (48 h LC50 = > 1000 mg/L). In another 48 h static acute toxicity study (McAllister 1978) Daphnia magna were exposed to nominal test concentrations of 0, 560, 1000, 1800, 3200 and 5600 mg/L. The 48 h LC50 was determined to be 6000 mg/L. A white precipitation was observed in all concentrations greater than 1000 mg/L. The 48 h LC50 value quoted in the report was 6000 mg/L. However this value is considered above the reported solubility of cyanuric acid. The 48 h LC50 is therefore considered to be >1000 mg/L. No mortalities were observed at this concentration. In an acute toxicity study with marine aquatic invertebrates (Anderson 2002) mysid shrimp were exposed to nominal concentrations of 0, 500, 1000, 2000, 4000 and 8000 mg/L cyanuric acid for 96 h. The 96 h LC50 was calculated to be 4438 mg/L.