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No data regarding the aquatic toxicity of dichromium tris(chromate) are available. A read across to chromium (III) hydroxide sulphate is proposed because environmental exposure to Cr (III) only is anticipated, and dichromium tris(chromate) is not released directly into the environment; the most likely pathway of environmental exposure from dichromium tris(chromate) is secondary exposure to receiving compartments via the STP. Whilst dichromium tris(chromate) contains both Cr (III) and Cr (VI) moieties, all Cr (VI) fractions are reduced to Cr (III) in the waste stream, prior to release. Also, Cr (VI) present in the environment is converted to Cr (III) by photochemical and redox processes. At the most common and environmentally relevant pH levels (between 6 and 9), and redox conditions, nearly all chromium present is predicted to exist in the form of Cr(OH)3, with the chromium itself existing in the trivalent state. Therefore, a read across from other similar chromium containing compounds (i.e. chromium hydroxide sulphate) that will give rise to Cr(OH)3 can be considered appropriate; with results being expressed in terms of total chromium, the toxic effect in the environment will be attributable directly to the concentration and oxidative state of the chromium present.

A study of the acute toxicity of 'Chromosal B' (chromium hydroxide sulphate) to fish was conducted with zebra fish (B. rerio) exposed to nominal concentrations of 'Chromosal B' ranging from 4526 to 10000 mg/L for 96 hours under semi-static conditions, with renewal of pH-adjusted media at 24 -h intervals (Caspers, 1988). The 96 hour LC50 of 'Chromosal B' was >10000 mg/L, based on the highest nominal concentration applied in the test. Based on the absence of abnormal swimming behaviour, the 96 h NOEC was 10000 mg/L (nominal). The solubility of 'Chromosal B' was low under the conditions of the test. Based on the mean measured concentration of dissolved chromium at the maximum concentration of 'Chromosal B', the 96 hour LC50 was >3.21 mg Cr/L.

A study of the long-term toxicity of 'basisches Chromsulfat' (chromium hydroxide sulphate) to fish was conducted in a 30-day early life-stage test with embryonic and hatched juvenile zebra fish (B. rerio) exposed to nominal concentrations of 'basisches Chromsulfat' ranging from 3.2 to 1000 mg/L under semi-static conditions, with renewal of pH-adjusted media at 48 -72-h intervals (Adema & de Ruiter, 1990). The 30 -day NOEC of 'basisches Chromsulfat' was 1000 mg/L, based on the highest nominal concentration applied in the test and the absence of adverse effects on hatch, survival, growth and behaviour of the test organisms. The solubility of 'basisches Chromsulfat' was low under the conditions of the test. Based on the maximum mean measured concentration of dissolved chromium recorded in any of the 'basisches Chromsulfat' treatments, the 30 day NOEC was 0.018 mg Cr/L.

There are no data available regarding the short-term toxicity of dichromium tris(chromate) to aquatic invertebrates. Short-term LC50s reported in the WHO (2009) for other Cr (III) compounds range from 0.1 mg/L (Daphnia pulex) to 442 mg/L (Asellus aquaticus) for freshwater invertebrates, and from 10 to 100 mg/L for marine invertebrates. Trivalent chromium is reported to be more toxic in soft waters than hard waters.

A study of the chronic toxicity of 'Chromosal B' (chromium hydroxide sulphate) to Daphnia magna was conducted with adult female test organisms exposed for 21 days to nominal concentrations of dissolved chromium ranging from 0.0020 to 0.0200 mg/L under semi-static conditions (Caspers, 1989). Based on the absence of treatment-related adult mortality or adverse impact on numbers of juveniles per adult daphnid, the mortality and reproductive EC50 values were both greater than 0.0200 mg Cr/L, the highest nominal concentration tested. Samples of fresh and expired media were taken at intervals during the study and analysed by atomic absorption spectrometry. After subtraction of the mean background concentration of chromium in the untreated control, the mean measured concentrations of dissolved Cr were 0.0010, 0.0041 and 0.0144 mg Cr/L at nominal concentrations of 0.020, 0.0063 and 0.0200 mg/L, respectively. Based on mean, background-corrected concentrations, the mortality and reproductive EC50 values were both >0.0144 mg Cr/L (measured).

A study was performed to assess the effects of Chromium (III) hydroxide sulphate on the Desmodesmus subspicatus. The study was conducted in accordance with Commission Regulation (EC) No 761/2009 amending Regulation No 440/2008, Method C.3 ‘Freshwater Algae and Cyanobacteria, Growth inhibition test’ (2009) which is equivalent to OECD Guideline for Testing of Chemicals No. 201 (2006). Exponentially growing algal cells were exposed for a period of 72 hours to a range of concentrations, nominally 0.0032, 0.01, 0.032, 0.1, 0.32, 1.0, 3.2, 32 and 100 mg/L. Initial measured concentrations were 1.28, 4.01, 8.89, 15.47, 52.49, 173.33, 327.53, 313.72, 637.73 and 848.61 µg/L. Measured values in the test media declined at subsequent analytical sampling intervals.  The results of the study are based on the initial measured concentrations; this is recommended in the guideline in those cases, where there is a decrease in concentration of test item over time, which is not accompanied by a decrease in toxicity over time. The 72 hour ErC50of chromium (III) hydroxide sulphate was > 848.6 µg/L, the corresponding no-observed effect concentration (NOEC) was 4.01 µg/L. The 72 hour EyC50of chromium (III) hydroxide sulphate was 76.1 µg/L, the corresponding NOEC was 4.01 µg/L

The effect of 'Chromosal B' (chromium hydroxide sulphate) on aerobic biological sewage treatment processes was assessed according to ISO Standard 8192 (equivalent to OECD Guideline 209 and ETAD method 103), by determining inhibition of respiration of the mixed community of microorganisms present in a sample of activated sludge (Caspers, 1988). Activated sludge obtained from a laboratory unit was exposed over a period of three hours to 'Chromosal B' weighed directly into the appropriate test vessels at nominal concentrations of 0 (control), 1000, 1800, 3200, 5600 and 10000 mg/L. A pair of test vessels was allocated to the control and the test substance treatments were run singly. There was also an un-inoculated abiotic control containing 10000 mg 'Chromosal B'/L and the reference inhibitor 3,5 -dichlorophenol was run at concentrations of 1.0 and 20.0 mg/L. No respiration inhibition, relative to the mean control rate, occurred in any of the 'Chromosal B' treatments and the 3 -h EC50 was therefore >10000 mg 'Chromosal B'/L, the highest concentration tested.