Aluminium sulphate

Short-term toxicity to fish

Description of key information

The pH significantly alters the speciation and therefore bioavailability of the aluminium such that acutely toxic concentrations occur below a pH of 6 but that above 6 the bioavailable concentration necessary to achieve mortality to fish in an acute study cannot be achieved.

Additional information

Five valid studies on fish were available on two aluminium salts:

Aluminum sulphate

Two short-term studies with fish are available on the 14-hydrated salt. Both tests were performed with Danio rerio. One test was a static study without pH adjustment. In this test an LC50 was found of 1 mg/l (dissolved Al) equivalent to 9.4 mg/L total aluminium at a pH of approximately 5.

The second test was performed under semi-static conditions with pH adjustment. The test substance concentrations were in a range of 62.5 to 1000 mg/l (nominal), eqivalent to 4.87 to 85.9 mg/L Total aluminium (measured) resulting in dissolved aluminum concentrations of 0.247 to 0.105 mg/l (the dissolved Al concentration decreased with increasing nominal concentrations). The pH was maintained at approximately 7.5. No effects were found in this test, therefore, LC50 is greater than 0.247 mg/l (dissolved Al) equivalent to 85.9 mg/L total aluminium , which was the maximum soluble concentration under the test conditons.

One supporting study from Kimball (1978) is available on the aluminium sulphate 16-hydrated salt. The nominal concentrations found that led to the 96 h LC50 are in line with those from the other studies.

 

Aluminum chloride, basic

Two short-term studies with fish are available. Both tests were performed with Danio rerio. One test was static without pH adjustment. In this test at a pH between 4.7 and 8.3 an LC50 was found of 186 mg/L nominal corresponding to 1.39 mg/l (dissolved Al) or 16.9 mg/L Total aluminium (measured). However, there was a strong division in pH across the test with nominal concentrations of 250 mg/L or higher at pH <5 and nominals at 125 mg/L or below at pH greater than or equal to 6.9. All fish at pH <5 died within 24 h of exposure while all fish at pH6.9 or above survived throughout the study.

The second test was semi-static with pH adjustment. The test substance concentrations were in a range of 62.5 to 1000 mg/l (nominal), this resulted in dissolved aluminum concentrations of 0.082 to 0.156 mg/l and 5.25 to 87.5 mg/L Total aluminium (measured). The pH was between 7.5 and 8.2 and 7.5 to 7.9 at the highest concentration at which no effects were found, therefore, LC50 is greater than 0.156 mg/l (dissolved Al) and 87.5 mg/L Total aluminium (measured).

Conclusion

Of the four available valid studies, two find no effects at the end of the study with Total aluminium concentrations of at least 85.9 mg/L (up to 87.5) and dissolved concentrations measured at a minimum of 0.156 mg/L (up to 0.247 mg/L) elemental Al. These studies were performed under standard Guidleine conditions at a pH between 7.5 and 8. In the two remaining studies, effects were found with Total alumuinium concentrations between 9.4 and 16.9 mg/L and dissolved aluminium concentrations ranging from 1 to 1.39 mg/L. In these cases the pH was not corrected to Guideline recommended values in the study and significant reduction of pH below 6 (at approximately 5) occurrred in solutions where immobilisation was observed.Thus it can be concluded that the pH significantly alters the speciation and therefore bioavailability of the aluminium such that acutely toxic concentrations occur below a pH of 6 but that above 6 the bioavailable concentration necessary to achieve mortality to fish in an acute study cannot be achieved.