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Toxicity to microorganisms

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Description of key information

The 3h EC50 and EC10 of anhydrous aluminium chloride in an activated sludge respiration inhibition study were both >1000 mg/L, equivalent to >200 mg/L as Total aluminium

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
200 mg/L

Additional information

Three valid studies on toxicity to microorganisms on four different aluminium salts were available:

Aluminium sulphate-18 -hydrate (7781 -31 -8) and Aluminium nitrate

The acute toxic effects of aluminium (Al) to the ciliated protozoa Tetrahymena pyriformis GL (TP) were investigated after an exposure of 9 h, a time which normally allowed three generations of T. pyriformis in control culture to be obtained. Al was administered under the soluble forms of three salts (AlCl3, Al(NO3)3, Al2(SO4)3) and the fine particles of an insoluble salt (Al2O3). A significant and a dose-dependent inhibition of the growth rate and of the motility was observed with TP exposed to Al compounds. The IC50 values of Al were ranked between 10 and 15 mg Al/L (10 mg/L for Al2(SO4)3; 14 mg/L for Al(NO3)3 and 15 mg/L for ALCl3), which is a difference of 1.5 times. As the concentrations appear to be based on total aluminium and no aluminium analysis was performed, these data provide supporting evidence that the the toxicity of soluble aluminium salts can be used for read across purposes. The IC50 increased to 495 mg Al/L with the insoluble salt, Al2O3. However, only IC50 values are reported and an insufficient number of concentrations and information on replicates are reported to allow accurate determination of an EC10. For this reason the study is used as supporting evidence for read-across between soluble aluminium salts.

Aluminum chloride anhydrous (7446 -70 -0)

One activated sludge respiration inhibition test following OECD 209 to GLP is available. This test was performed with anhydrous aluminium chloride. A stock solution was prepared and then serially diluted to prepare the following 5 test concentrations 62.5, 125, 250, 500, 1000 mg/l nominal together with a control. The pH of each test solution was adjusted to 7.2-7.3 prior to addition of the sludge in order to be equivalent to that of the control samples and the test performed for 180 minutes. The pH was measured in the sludge samples at the end of the study and were found to be between 7.8 and 8.1. No effects compared to the control were observed on respiration at any of the concentrations leading to a NOEC/ EC10 and EC50 all greater than 1000 mg/L nominal, equivalent to a Total aluminium concentration of >200 mg/L.

 

Polyaluminum chloride hydroxide sulphate (39290 -78 -3)

One activated sludge respiration inhibition test is available. This test was performed with aluminum chloride hydroxide sulfate according to a standard guideline. It was performed as limit test at 100 mg/l test material. The test substance contained 4.4% Al and the test concentrations can be converted to mg/l Al. 100 mg/l test material is equal to 4.4 mg/l Al. No effects were found on respiration at the highest concentration tested. The NOEC can therefore be considered to be greater than or eaqual to 4.4 mg/L.

Conclusion

Several studies are available to determine the toxicity of Total aluminium on sludge. ASRIT studies did not find effects at the maximum concentration tested, with no effects in the key study at 200 mg/L as Total aluminium. In a study on Tetrahymena pyriformis, a much lower EC50 was found for three soluble aluminium salts tested. However, the notable difference in this case was that while the ASRIT studies were performed at a pH between 7 and 8, the Tetrahymena studies were adjusted to 6.5. As the pH found in a WWTP is expected to be close to 8 (as was the case in the sludge samples from the ASRIT study measured at the end of the test), and aluminium is expected to be less toxic (as less bioavailable) at pH 7 to 8 than at pH 6.5, as toxicity is influenced by DOC, which would also be very high in a WWTP and as ASRIT studies did not indicate potential for malfunctioning of WWTPs, the Tetrahymena studies are used only as supporting data while the NOEC/EC10 is based on the ASRIT study.