Strontium chromate

Toxicity to microorganisms

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.

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

Micro-organism	Substance	Method	Endpoint (mg Cr/L)	Reference
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 PNEC_{micro-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 PNEC_{micro-organism} is proposed to be 10 mg Cr(III)/L.