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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

Two sources of information have been used to propose the PNECmicro-organism: study according to ISO Standard 8192 with potassium chromium sulphate dodecahydrate (as a worst-case, soluble Cr(III) salt) and the EU RAR (2005) in which five studies are tabulated and were used to propose a PNECmicro-organism.

Key value for chemical safety assessment

Additional information

EU RAR (2005)

A concentration of 10 mg Cr(III)/L promoted growth in some species of bacteria, and 100 mg Cr(III)/L produced only a small amount of growth inhibition. The study did not provide a formal NOEC; it is proposed to use 10 mg Cr(III)/L as the PNEC for chromium (III).

From: Appendix F: EU RAR (2005), Vol. 53: Table F.3 Summary of the ecotoxicological data for chromium (III) to bacteria




(mg Cr/L)


Activated sludge

Chromium hydroxide sulphate

ISO 8192-inhibition of oxygen consumption

3 hour NOEC > 3130

IUCLID, 1999

Azobacter vinelandii (soil bacterium)

Chromic chloride

Growth inhibition

over 4 days

LOEC/NOEC ~ 0.26

Ueda et al., 1988

Fusarium oxysporum (soil fungus)

Chromic chloride

Growth inhibition

over 27 hours

NOEC > 6.5

Ueda et al., 1988

Pseudomonas fluorescens

Dichromium trioxide

24h-NOEC >6,840

IUCLID, 1999

Pseudomonas fluorescens

Chromium hydroxide sulphate

24h-NOEC >313

IUCLID, 1999

The effect of 'Kaliumchromalaun' (potassium chromium sulphate dodecahydrate) 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. Activated sludge obtained from a laboratory unit was exposed over a period of three hours to 'Kaliumchromalaun' weighed directly into the appropriate test vessels at nominal concentrations of 0 (control), 100, 1000 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 uninoculated abiotic control containing 10000 mg 'Kaliumchromalaun'/L and the reference inhibitor 3,5 -dichlorophenol was run at concentrations of 1.0 and 20.0 mg/L. No significant respiration inhibition, relative to the mean control rate, occurred in any of the 'Kaliumchromalaun' treatments and the 3-hour EC50 was therefore >10000 mg 'Kaliumchromalaun'L, the highest concentration tested.

The chromium content of potassium chromium sulphate dodecahydrate  (KCr(SO4)2*12H2O) is approximately 10%, therefore, the 3-hour EC50 is equivalent to > 100 mg Cr/L.  This is consistent with the EU RAR PNECmicro-organism and is highly likely to be overprotective of the hazard of the relatively insoluble Cr(III)oxide.

Given that the EU RAR proposal is based on a greater amount of data than the one study on potassium chromium sulphate dodecahydrate, the PNECmicro-organism is proposed to be 10 mg Cr(III)/L.